Chapter: Embryology; Topic: Development of the Nervous System; Subtopic: Derivatives of the Neural Tube and Neural Crest
Key Definitions & Concepts
Neural Tube: The embryonic precursor to the Central Nervous System (Brain and Spinal Cord), Retina, Posterior Pituitary, and Pineal Gland.
Neural Crest Cells: Often called the "fourth germ layer," these migratory cells form the Peripheral Nervous System (DRG, Autonomic ganglia), Schwann cells, Melanocytes, and Adrenal Medulla.
Neurulation: The folding process in vertebrate embryos in which the neural plate is transformed into the neural tube.
Neuropores: Openings at the cranial and caudal ends of the neural tube; failure to close results in neural tube defects (Anencephaly, Spina Bifida).
Alar Plate: The dorsal portion of the neural tube that differentiates into sensory processing structures.
Basal Plate: The ventral portion of the neural tube that differentiates into motor neurons.
Hirschsprung Disease: A congenital condition caused by the failure of neural crest cells to migrate to the distal colon (aganglionic megacolon).
Retina: An outgrowth of the diencephalon, making it a direct derivative of the neural tube, not the neural crest or surface ectoderm.
Schwann Cells: Glial cells of the PNS derived from the Neural Crest (unlike Oligodendrocytes of the CNS, which are Neural Tube derivatives).
Adrenal Medulla: Derived from Neural Crest cells (modified sympathetic ganglia), secreting catecholamines.
Lead Question - 2016
Which of the following is derived from the neural tube except?
a) Retina
b) Brain
c) Dorsal root ganglia
d) Pineal gland
Explanation: The nervous system develops from the ectoderm. The neural plate folds to form the Neural Tube, which gives rise to the Central Nervous System (Brain, Spinal Cord), the Retina (as an optic cup outgrowth), the Posterior Pituitary (Neurohypophysis), and the Pineal Gland. As the neural tube closes, cells at the crest of the folds migrate away; these are the Neural Crest cells. Neural Crest cells give rise to the Peripheral Nervous System, including the Dorsal Root Ganglia, sympathetic chain ganglia, Schwann cells, and adrenal medulla. Therefore, the dorsal root ganglia are neural crest derivatives, not neural tube. The correct answer is c) Dorsal root ganglia.
1. A newborn presents with a tuft of hair over the lumbar spine. Radiological evaluation reveals a bony defect in the vertebral arch. This condition, Spina Bifida Occulta, results from defective closure of the:
a) Cranial Neuropore
b) Caudal Neuropore
c) Neural Crest migration
d) Notochordal process
Explanation: The neural tube closes bi-directionally. The open ends are the neuropores. The Caudal Neuropore is the last to close (around day 27-28). Failure of the caudal neuropore to close completely or induce proper formation of the overlying vertebral arch leads to Spina Bifida. The mildest form, Spina Bifida Occulta, presents with a hairy patch and a vertebral arch defect. Failure of the Cranial Neuropore leads to Anencephaly. Neural crest migration issues cause neurocristopathies like Hirschsprung's. Notochord defects affect the vertebral body/nucleus pulposus. Therefore, the correct answer is b) Caudal Neuropore.
2. Which of the following glial cells is derived from the Neural Crest?
a) Astrocytes
b) Oligodendrocytes
c) Ependymal cells
d) Schwann cells
Explanation: There is a distinct embryological divide between the supporting cells of the CNS and PNS. The glia of the Central Nervous System (Astrocytes, Oligodendrocytes, and Ependymal cells) are derived from the Neuroepithelium of the Neural Tube (Microglia are the exception, derived from Mesoderm/Monocytes). In contrast, the glia of the Peripheral Nervous System, specifically the Schwann cells (and satellite cells of ganglia), are derived from Neural Crest cells that migrate along with the growing axons. This distinction explains why Schwannomas are often associated with other neural crest disorders (e.g., Neurofibromatosis). Therefore, the correct answer is d) Schwann cells.
3. A 2-day-old infant fails to pass meconium. Contrast enema shows a "transition zone" with a dilated proximal colon and a narrow distal segment. Rectal biopsy reveals an absence of ganglion cells in the myenteric plexus. These missing cells are derived from:
a) Neural Tube
b) Surface Ectoderm
c) Neural Crest
d) Endoderm
Explanation: The clinical picture is Hirschsprung Disease (Congenital Aganglionic Megacolon). The enteric nervous system (Meissner's and Auerbach's plexuses) is formed by Neural Crest cells (specifically vagal and sacral neural crest) that migrate into the gut wall during development. In Hirschsprung disease, these cells fail to migrate to the distal-most part of the colon (rectum/sigmoid). Without these inhibitory ganglion cells, the smooth muscle cannot relax, leading to obstruction and proximal dilation. Since the ganglion cells are neural crest derivatives, this is a neurocristopathy. Therefore, the correct answer is c) Neural Crest.
4. The adrenal gland has a dual embryological origin. The cells of the Adrenal Medulla, which secrete epinephrine, are derived from:
a) Intermediate Mesoderm
b) Neural Crest
c) Surface Ectoderm
d) Endoderm
Explanation: The adrenal cortex and medulla have different origins. The Adrenal Cortex is derived from the Intermediate Mesoderm (coelomic epithelium). The Adrenal Medulla is effectively a modified sympathetic ganglion. It contains Chromaffin cells which are postganglionic sympathetic neurons that have lost their axons and secrete catecholamines directly into the blood. As sympathetic ganglia are derivatives of the Neural Crest, the adrenal medulla is also a neural crest derivative. This explains why Pheochromocytomas (tumors of the medulla) are linked to other neural crest tumors (MEN syndromes). Therefore, the correct answer is b) Neural Crest.
5. The retina of the eye is embryologically an extension of the:
a) Surface Ectoderm
b) Mesoderm
c) Diencephalon (Neural Tube)
d) Neural Crest
Explanation: The eye development involves multiple layers. The lens and corneal epithelium come from Surface Ectoderm. The choroid and sclera come from Mesoderm/Neural Crest. However, the neural sensory layer, the Retina, and the optic nerve are direct outgrowths of the forebrain (specifically the Diencephalon). They form as optic grooves, then optic vesicles, and finally optic cups. Since the diencephalon is part of the Neural Tube, the retina is considered a Neural Tube derivative (part of the CNS). This is why the optic nerve is ensheathed by meninges. Therefore, the correct answer is c) Diencephalon (Neural Tube).
6. A patient presents with a white forelock of hair, heterochromia iridis (different colored eyes), and congenital sensorineural deafness. This condition (Waardenburg Syndrome) involves a defect in cells derived from:
a) Neural Crest
b) Neural Tube
c) Otic Placode
d) Pharyngeal Endoderm
Explanation: Waardenburg Syndrome is a classic Neurocristopathy. Neural Crest cells differentiate into Melanocytes, which migrate to the skin, hair follicles, iris, and the stria vascularis of the inner ear. A defect in neural crest migration or survival leads to depigmentation (white forelock, pale/mismatched eyes) and cochlear dysfunction (deafness due to lack of melanocytes in the stria vascularis). While the inner ear sensory cells come from the Otic placode, the melanocyte defect causing the syndrome is Neural Crest. Therefore, the correct answer is a) Neural Crest.
7. The motor neurons of the spinal cord (anterior horn cells) develop from which zone of the developing neural tube?
a) Alar Plate
b) Basal Plate
c) Roof Plate
d) Floor Plate
Explanation: The neural tube is divided functionally by the Sulcus Limitans. The dorsal region is the Alar Plate, which processes sensory information (dorsal horn). The ventral region is the Basal Plate, which differentiates into motor neurons (ventral/anterior horn). The Roof plate and Floor plate are primarily signaling centers (producing BMP and SHH respectively) that guide this dorsal-ventral patterning but do not give rise to the neurons themselves. Thus, all somatic and autonomic motor neurons in the CNS arise from the Basal Plate. Therefore, the correct answer is b) Basal Plate.
8. Which of the following skeletal structures is derived from the Neural Crest (Ectomesenchyme) rather than Mesoderm?
a) Vertebrae
b) Ribs
c) Mandible
d) Femur
Explanation: Generally, bones and connective tissue are derived from Mesoderm. However, in the head and neck, Neural Crest cells migrate into the pharyngeal arches and form the "Ectomesenchyme." This ectomesenchyme gives rise to the bones of the face (viscerocranium), including the maxilla, Mandible, zygomatic bone, and the auditory ossicles. The bones of the skull base and the post-cranial skeleton (vertebrae, ribs, limbs) are derived from Paraxial Mesoderm (Somites) and Lateral Plate Mesoderm. Therefore, the correct answer is c) Mandible.
9. The Parafollicular C cells of the thyroid gland, which secrete Calcitonin, migrate into the thyroid from the Ultimobranchial body. These cells are originally derived from:
a) Thyroid diverticulum (Endoderm)
b) Neural Crest
c) Paraxial Mesoderm
d) 3rd Pharyngeal Pouch
Explanation: The thyroid follicular cells are endodermal, arising from the foramen cecum. However, the Parafollicular C cells have a different origin. They are Neural Crest derivatives that migrate into the Ultimobranchial body (from the 4th/5th pharyngeal pouch) and then become incorporated into the thyroid gland. This embryological origin is clinically significant because Medullary Thyroid Carcinoma (a tumor of C cells) is often associated with MEN syndromes, which involve other neural crest tumors like Pheochromocytoma. Therefore, the correct answer is b) Neural Crest.
10. A pregnant woman takes high doses of isotretinoin (Vitamin A) for acne. This drug is highly teratogenic primarily because it disrupts the expression of HOX genes, affecting the migration and development of:
a) Neural Tube
b) Neural Crest cells
c) Notochord
d) Intermediate Mesoderm
Explanation: Retinoic acid is a crucial signaling molecule for anterior-posterior patterning. High levels of Isotretinoin are toxic to Neural Crest cells (Cranial Neural Crest). This leads to a characteristic pattern of birth defects known as Retinoic Acid Embryopathy, which includes craniofacial dysmorphism (microtia, cleft palate), thymic aplasia, and cardiac outflow tract defects (conotruncal defects). All these structures (face, thymus stroma, conotruncal septum) rely on cranial neural crest contribution. While neural tube defects can occur with folate deficiency, retinoids specifically target the crest. Therefore, the correct answer is b) Neural Crest cells.
Chapter: Upper Limb Anatomy; Topic: Development of Hand; Subtopic: Ossification of Carpal Bones
Keyword Definitions:
Carpal Bones: Eight small bones of the wrist arranged in proximal and distal rows.
Ossification Centers: Sites where bone tissue begins to develop; carpal bones ossify postnatally.
Capitate & Hamate: First carpal bones to ossify, appearing in the first year of life.
Carpal Ossification Sequence: A predictable pattern used clinically to assess bone age.
Bone Age Assessment: Radiographic evaluation comparing ossification with chronological standards.
1) Lead Question – 2016
Four carpal bones are present at what age?
A) 3 years
B) 4 years
C) 5 years
D) 6 years
Answer: A) 3 years
Explanation: Carpal bones ossify in a specific chronological sequence. Capitate and hamate appear first within the first year of life. By 2–3 years of age, two additional carpal bones typically ossify, bringing the total to four. Radiological evaluation of wrist ossification assists in assessing delayed growth or endocrine abnormalities. By this standard timeline, four ossified carpal bones are present at approximately 3 years of age, making option A the correct answer. Understanding carpal bone ossification is crucial for pediatric age estimation and orthopedic assessments.
2) Which carpal bone ossifies first?
A) Pisiform
B) Hamate
C) Capitate
D) Scaphoid
Answer: C) Capitate
Explanation: Capitate ossifies first, followed closely by hamate, both within the first year. Thus, C is correct.
3) The last carpal bone to ossify is–
A) Triquetrum
B) Pisiform
C) Lunate
D) Trapezium
Answer: B) Pisiform
Explanation: Pisiform ossifies around 9–12 years, making it the last carpal bone. Thus, B is correct.
4) A 1-year-old child's wrist x-ray commonly shows which carpal bones?
A) Capitate & hamate
B) Scaphoid & lunate
C) Trapezoid only
D) Triquetrum only
Answer: A) Capitate & hamate
Explanation: These two bones ossify first. Thus, A is correct.
5) In a 5-year-old child, the number of ossified carpal bones expected is–
A) 2
B) 4
C) 6
D) 8
Answer: C) 6
Explanation: By 5 years, about six carpal bones appear radiographically. Thus, C is correct.
6) Carpal ossification helps diagnose–
A) Diabetes mellitus
B) Growth delay
C) Pneumonia
D) Appendicitis
Answer: B) Growth delay
Explanation: Bone age assessment via carpal ossification is essential in endocrinology. Thus, B is correct.
7) Pisiform is considered a–
A) Long bone
B) Sesamoid bone
C) Flat bone
D) Irregular bone
Answer: B) Sesamoid bone
Explanation: Pisiform is a sesamoid bone within flexor carpi ulnaris tendon. Thus, B is correct.
8) Scaphoid receives blood supply mainly from–
A) Volar vessels
B) Dorsal carpal branch
C) Ulnar artery
D) Radial recurrent artery
Answer: B) Dorsal carpal branch
Explanation: Scaphoid vascularity is predominantly dorsal, explaining AVN risk. Thus, B is correct.
9) A triquetral fracture is commonly detected by–
A) MRI
B) Lateral wrist x-ray
C) Ultrasound
D) AP wrist x-ray
Answer: B) Lateral wrist x-ray
Explanation: Triquetral fractures show dorsal chip fragments best in lateral view. Thus, B is correct.
10) Carpal bone forming the floor of the anatomical snuffbox is–
A) Pisiform
B) Scaphoid
C) Hamate
D) Capitulum
Answer: B) Scaphoid
Explanation: Scaphoid lies beneath snuffbox; tenderness here suggests fracture. Thus, B is correct.
11) In children, isolated carpal fractures are rare because–
A) Carpal bones are cartilaginous
B) Radius absorbs most force
C) Ligaments are loose
D) Forearm muscles protect the wrist
Answer: A) Carpal bones are cartilaginous
Explanation: In early childhood, carpal bones are still cartilaginous and resistant to fracture. Thus, A is correct.
Chapter: Embryology & Orthopedics; Topic: Bone Development; Subtopic: Types of Epiphyses
Keyword Definitions:
Pressure Epiphysis: Epiphysis involved in transmission of weight or pressure, e.g., head of femur.
Traction Epiphysis: Site where strong muscle pull occurs; develops due to traction forces (e.g. mastoid process).
Atavistic Epiphysis: Epiphysis representing a phylogenetic remnant, e.g., coracoid process.
Accessory Epiphysis: Additional epiphysis appearing occasionally, e.g., os trigonum.
Secondary Ossification Center: Center forming epiphysis after primary diaphyseal ossification.
1) Lead Question – 2016
Which of the following is a traction epiphysis?
A) Distal Radius
B) Mastoid process
C) Tibial Condyles
D) Coracoid Process
Answer: B) Mastoid process
Explanation: Traction epiphyses develop due to the pulling force exerted by attached muscles. The mastoid process is a classical example because the sternocleidomastoid muscle exerts strong traction, stimulating its secondary ossification. Distal radius and tibial condyles are pressure epiphyses involved in weight transmission, while the coracoid process is an atavistic epiphysis. Therefore, B is correct. Understanding epiphyseal types helps interpret growth patterns, skeletal development, and orthopedic conditions affecting growth centers.
2) Which of the following is an example of pressure epiphysis?
A) Greater trochanter
B) Head of femur
C) Mastoid process
D) Coracoid process
Answer: B) Head of femur
Explanation: Pressure epiphyses are involved in weight transmission across joints. The head of the femur is a classic pressure epiphysis because it participates in hip joint loading. The greater trochanter is a traction epiphysis, mastoid process also traction, and coracoid process is atavistic. Thus, B is correct, demonstrating the functional classification of epiphyses.
3) A patient suffers avulsion injury at the greater trochanter. This region is classified as–
A) Pressure epiphysis
B) Traction epiphysis
C) Atavistic epiphysis
D) Accessory epiphysis
Answer: B) Traction epiphysis
Explanation: The greater trochanter develops due to traction exerted by gluteal muscles. Avulsion fractures commonly occur at traction epiphyses where strong tendon pull is present. It is not a pressure or accessory epiphysis. Thus, B is correct.
4) The coracoid process is an example of–
A) Pressure epiphysis
B) Atavistic epiphysis
C) Traction epiphysis
D) Pathological epiphysis
Answer: B) Atavistic epiphysis
Explanation: The coracoid process represents a phylogenetic remnant, considered an atavistic epiphysis. It does not function primarily under pressure or traction. Thus, B is correct.
5) Which of the following is a traction epiphysis in the humerus?
A) Capitulum
B) Greater tubercle
C) Trochlea
D) Medial epicondyle
Answer: B) Greater tubercle
Explanation: The greater tubercle serves as the attachment for rotator cuff muscles, making it a traction epiphysis. Capitulum and trochlea are pressure epiphyses; medial epicondyle is an apophysis but traction is less significant. Thus, B is correct.
6) A radiograph of a child’s skull shows delayed development of mastoid process. This affects attachment of–
A) Trapezius
B) Sternocleidomastoid
C) Masseter
D) Temporalis
Answer: B) Sternocleidomastoid
Explanation: The SCM inserts into the mastoid process, which forms as a traction epiphysis. Delay in mastoid development may impair muscle attachment. Thus, B is correct.
7) Which of the following is an example of an accessory epiphysis?
A) Os trigonum
B) Tibial condyle
C) Mastoid process
D) Greater trochanter
Answer: A) Os trigonum
Explanation: The os trigonum is an accessory epiphysis occurring posterior to the talus. Tibial condyles are pressure epiphyses; mastoid and trochanter are traction epiphyses. Thus, A is correct.
8) Traction epiphysis forms due to–
A) Weight-bearing pressure
B) Muscle pull
C) Hormonal influence
D) Nutrient artery pattern
Answer: B) Muscle pull
Explanation: Continuous pull from attached muscles stimulates ossification centers forming traction epiphyses. Pressure epiphyses form from weight-bearing. Thus, B is correct.
9) The tibial tuberosity is classified as–
A) Pressure epiphysis
B) Traction epiphysis
C) Atavistic epiphysis
D) Pathological epiphysis
Answer: B) Traction epiphysis
Explanation: The tibial tuberosity is the insertion site of the patellar ligament subject to strong muscle pull from the quadriceps, making it a traction epiphysis. Thus, B is correct.
10) A boy with Osgood–Schlatter disease has inflammation in a traction epiphysis located at the–
A) Distal femur
B) Tibial tuberosity
C) Calcaneal tuberosity
D) Radial head
Answer: B) Tibial tuberosity
Explanation: Osgood–Schlatter disease affects the tibial tuberosity, a traction epiphysis due to quadriceps pull. Distal femur is a pressure epiphysis; calcaneal tuberosity is apophyseal; radial head is pressure-related. Thus, B is correct.
11) Which structure represents a traction epiphysis of the scapula?
A) Glenoid cavity
B) Coracoid process
C) Inferior angle
D) Acromion
Answer: D) Acromion
Explanation: The acromion develops due to traction exerted by deltoid and trapezius muscles, making it a traction epiphysis. Coracoid is atavistic. Glenoid cavity is a pressure epiphysis. Thus, D is correct.
Chapter: Embryology; Topic: Pharyngeal Apparatus; Subtopic: Derivatives of Pharyngeal Pouches
Keyword Definitions:
Pharyngeal Pouches: Endoderm-lined outpouchings that give rise to lymphoid and endocrine structures.
Second Pharyngeal Pouch: Forms epithelial lining of palatine tonsil and tonsillar crypts including crypta magna.
Crypta Magna: Deepest and largest tonsillar crypt within the palatine tonsil.
Third Pouch: Forms inferior parathyroid glands and thymus.
Fourth Pouch: Forms superior parathyroid glands and ultimobranchial body (C-cells).
1) Lead Question – 2016
Crypta magna develops from which pouch?
A) 1st
B) 2nd
C) 3rd
D) 4th
Answer: B) 2nd
Explanation: The palatine tonsil and its epithelial crypts, including the deepest one known as crypta magna, arise from the endoderm of the second pharyngeal pouch. The first pouch forms the auditory tube and middle ear cavity, the third forms thymus and inferior parathyroids, and the fourth forms superior parathyroids and ultimobranchial body. Thus, the correct answer is B. Understanding pouch derivatives is essential for interpreting congenital anomalies of the head and neck.
2) Palatine tonsil epithelium originates from–
A) 1st pouch
B) 2nd pouch
C) 3rd pouch
D) 4th pouch
Answer: B) 2nd pouch
Explanation: Palatine tonsil epithelium is derived from the second pharyngeal pouch. This endodermal lining proliferates to form tonsillar crypts. The first pouch forms Eustachian tube and middle ear. Third and fourth pouches form parathyroids and thymus. Hence, B is correct.
3) A child with recurrent tonsillitis shows enlarged tonsillar crypts. These crypts are derived from which embryologic tissue?
A) Endoderm of 2nd pouch
B) Ectoderm of clefts
C) Neural crest
D) Mesoderm
Answer: A) Endoderm of 2nd pouch
Explanation: Tonsillar crypts, including crypta magna, arise from endoderm of the second pouch. Ectoderm forms external clefts, neural crest forms connective tissues of arches, and mesoderm forms muscles. Thus, A is correct.
4) Which structure is derived from the first pharyngeal pouch?
A) Middle ear cavity
B) Palatine tonsil
C) Thymus
D) Superior parathyroids
Answer: A) Middle ear cavity
Explanation: The first pouch forms the tympanic cavity and auditory tube. The second forms tonsils, the third forms thymus/inferior parathyroids, and the fourth forms superior parathyroids. Thus, A is correct.
5) Thymus develops from which pouch?
A) 1st
B) 2nd
C) 3rd
D) 4th
Answer: C) 3rd
Explanation: The third pouch forms thymus (ventral wing) and inferior parathyroids (dorsal wing). Second pouch forms tonsils; first forms auditory structures; fourth pouch forms superior parathyroids. Thus, C is correct.
6) A newborn with DiGeorge syndrome has abnormal derivatives of which pouch?
A) 1st and 2nd
B) 2nd and 3rd
C) 3rd and 4th
D) Only 4th
Answer: C) 3rd and 4th
Explanation: DiGeorge syndrome involves failure of development of the third and fourth pouches leading to thymic aplasia and parathyroid defects. Tonsils (2nd pouch) remain normal. Thus, C is correct.
7) Ultimobranchial body is derived from which pouch?
A) 1st
B) 2nd
C) 3rd
D) 4th
Answer: D) 4th
Explanation: The ultimobranchial body forms parafollicular (C) cells of thyroid and arises from the fourth pouch. Thus, D is correct.
8) A lesion in superior parathyroid glands suggests abnormality of–
A) 1st pouch
B) 2nd pouch
C) 3rd pouch
D) 4th pouch
Answer: D) 4th
Explanation: Superior parathyroids originate from the fourth pouch. Inferior ones originate from the third pouch. Thus, D is correct.
9) Enlargement of crypta magna clinically presents as–
A) Recurrent otitis media
B) Dysphagia due to tonsillar hypertrophy
C) Nasal polyps
D) Conductive hearing loss
Answer: B) Dysphagia due to tonsillar hypertrophy
Explanation: Enlarged tonsillar crypts can cause obstructive symptoms including dysphagia. The other options relate to first pouch or nasal causes. Thus, B is correct.
10) The palatine tonsil lymphoid tissue infiltrates the epithelium derived from the–
A) First pouch
B) Second pouch
C) Third pouch
D) Fourth pouch
Answer: B) Second pouch
Explanation: Tonsillar lymphoid tissue invades the second pouch endodermal epithelium forming crypts. Thus, B is correct.
11) In tonsillectomy, bleeding is most likely from vessels associated with a structure derived from which pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: B) Second
Explanation: Palatine tonsils (second pouch derivatives) receive blood supply from tonsillar branches of facial artery, which commonly bleed during tonsillectomy. Thus, B is correct.
Chapter: Embryology; Topic: Development of Kidney; Subtopic: Abnormalities of Kidney Ascent
Keyword Definitions:
Kidney Ascent: Normal cranial migration of metanephric kidneys from pelvis to lumbar region.
Pelvic Kidney: Kidney that fails to ascend, remaining in the pelvis.
Horseshoe Kidney: Fusion anomaly, usually of lower poles, preventing normal ascent.
Aortic Branch Obstruction: One cause of impaired ascent due to vascular resistance.
Genetic Mutations: Rarely implicated; p53 mutation is not associated with kidney ascent abnormality.
1) Lead Question – 2016
Pelvic kidneys are due to all except?
A) Inability to ascend during fetal life
B) Fusion of the lower poles
C) Being blocked by branches of the aorta
D) p53 mutation
Answer: D) p53 mutation
Explanation: Pelvic kidneys occur when the metanephric kidneys fail to ascend from the pelvis to their normal lumbar position. This can happen due to mechanical obstruction by developing aortic branches or fusion of lower poles, as in horseshoe kidney, which prevents upward migration. Inability to ascend is therefore a common cause. However, p53 mutations are unrelated to kidney ascent and typically involve tumor suppression defects. Therefore, D is correct. Understanding embryologic kidney migration explains congenital anomalies such as ectopic kidney, horseshoe kidney, and aberrant renal vasculature.
2) Horseshoe kidney results from fusion of which renal poles?
A) Upper poles
B) Lower poles
C) Medial poles
D) Lateral poles
Answer: B) Lower poles
Explanation: Horseshoe kidney occurs when the lower poles of the metanephric kidneys fuse during ascent. This fused mass gets trapped under the inferior mesenteric artery, preventing normal migration. Upper pole fusion is extremely rare. Thus, B is correct. The anomaly is usually asymptomatic but may predispose to obstruction or infection.
3) A fused pelvic kidney is discovered in a newborn. The most likely cause is–
A) Failed metanephric induction
B) Arrested ascent of kidney
C) Absent ureteric bud
D) Excessive aortic branching
Answer: B) Arrested ascent of kidney
Explanation: Pelvic fusion anomalies generally arise when kidneys fail to ascend from the pelvis. Metanephric induction failure leads to renal agenesis; absent ureteric bud prevents kidney formation; excessive aortic branching contributes but does not fully explain fusion. Thus, B is correct. Pelvic kidney is often detected incidentally on imaging.
4) The structure that most commonly blocks ascent of a horseshoe kidney is–
A) Renal artery
B) Inferior mesenteric artery
C) Gonadal artery
D) Common iliac vein
Answer: B) Inferior mesenteric artery
Explanation: Horseshoe kidneys become trapped under the inferior mesenteric artery due to lower pole fusion. Renal or gonadal arteries develop later and do not obstruct ascent. Thus, B is correct. This anatomical relationship helps identify the condition on imaging.
5) A child presents with abdominal mass; imaging shows pelvic ectopic kidney. Which complication is more likely?
A) Hypertension
B) Hydronephrosis
C) Hypercalcemia
D) Acute pancreatitis
Answer: B) Hydronephrosis
Explanation: Pelvic kidneys have abnormal orientation and ureteric course, predisposing to obstruction and hydronephrosis. Hypertension is uncommon unless renal artery stenosis occurs. Hypercalcemia and pancreatitis are unrelated. Thus, B is correct, showing developmental malposition can lead to functional impairment.
6) Renal arteries in ectopic kidneys often arise from–
A) Abdominal aorta only
B) Iliac arteries
C) Superior mesenteric artery
D) Celiac trunk
Answer: B) Iliac arteries
Explanation: Pelvic kidneys commonly receive blood supply from iliac arteries because they do not ascend to the lumbar region where normal renal arteries originate. SMA and celiac trunk supply gut organs. Thus, B is correct, explaining atypical vasculature seen in ectopic kidneys.
7) Lack of kidney ascent is usually due to developmental abnormalities in the–
A) Dorsal mesentery
B) Vascular supply
C) Somites
D) Neural crest cells
Answer: B) Vascular supply
Explanation: Vascular changes, especially branches of the aorta, often impede kidney ascent. Somites and neural crest cells do not determine kidney ascent; dorsal mesentery relates to gut rotation. Thus, B is correct, emphasizing vascular influence on renal migration.
8) A patient with horseshoe kidney has increased risk of which disorder?
A) Turner syndrome
B) DiGeorge syndrome
C) Patau syndrome
D) Down syndrome
Answer: A) Turner syndrome
Explanation: Horseshoe kidney is associated with Turner syndrome (45,XO) more commonly than other chromosomal anomalies. Down and Patau syndromes have other systemic anomalies. Thus, A is correct, showing links between renal and chromosomal abnormalities.
9) In renal ectopia, which ureteric feature is commonly seen?
A) Shortened ureter
B) Abnormally long ureter
C) Blind-ending ureter
D) Duplicated ureter
Answer: B) Abnormally long ureter
Explanation: A kidney that fails to ascend remains pelvic, requiring a longer ureter to reach the bladder. Shortened or blind-ending ureters indicate agenesis; duplication arises from ureteric bud anomalies. Thus, B is correct, matching expected anatomical variation in ectopic kidneys.
10) Which embryonic tissue forms the ureteric bud?
A) Intermediate mesoderm
B) Endoderm
C) Ectoderm
D) Splanchnic mesoderm
Answer: A) Intermediate mesoderm
Explanation: The ureteric bud arises from the mesonephric duct, derived from intermediate mesoderm. Endoderm forms bladder epithelium; ectoderm forms skin; splanchnic mesoderm forms cardiac and visceral structures. Thus, A is correct.
11) Persistent pelvic kidney is most easily confused radiologically with–
A) Ovarian mass
B) Splenic cyst
C) Liver hemangioma
D) Pancreatic pseudocyst
Answer: A) Ovarian mass
Explanation: Pelvic kidneys may mimic adnexal masses on ultrasound or CT. Splenic, hepatic, and pancreatic lesions are upper abdominal. Thus, A is correct, emphasizing anatomical overlap in pelvic imaging.
Chapter: Cell Biology; Topic: Meiosis; Subtopic: Stages of Meiotic Prophase I
Keyword Definitions:
Meiosis: A specialized cell division producing haploid gametes from diploid germ cells.
Prophase I: Longest meiotic phase with distinct substages—leptotene, zygotene, pachytene, diplotene, diakinesis.
Leptotene: Chromosomes begin to condense into long thin threads.
Pachytene: Homologous chromosomes fully synapse; crossing over occurs.
Crossing Over: Exchange of genetic material during pachytene contributing to genetic diversity.
1) Lead Question – 2016
Leptotene and pachytene are stages of which phase of meiosis–
A) Prophase I
B) Metaphase I
C) Anaphase II
D) Telophase II
Answer: A) Prophase I
Explanation: Prophase I is the most complex phase of meiosis and is subdivided into leptotene, zygotene, pachytene, diplotene, and diakinesis. Leptotene marks early chromatin condensation, while pachytene involves synapsis of homologous chromosomes and crossing over. These events do not occur in metaphase I, anaphase II, or telophase II. Therefore, A is correct. Identifying these substages is essential in understanding the chromosomal behavior leading to genetic recombination and proper segregation during gametogenesis.
2) Crossing over occurs during which stage of meiosis?
A) Leptotene
B) Pachytene
C) Diakinesis
D) Metaphase I
Answer: B) Pachytene
Explanation: Pachytene is the stage in prophase I where homologous chromosomes are fully synapsed and crossing over occurs through chiasmata formation. Leptotene shows partial chromatin condensation; diakinesis involves terminalization of chiasmata; metaphase I aligns bivalents at the equator. Thus, B is the correct answer, underscoring the significance of pachytene in generating genetic variability.
3) A genetic disorder involving defective synaptonemal complex formation would most directly affect–
A) Zygotene
B) Anaphase I
C) Anaphase II
D) Telophase I
Answer: A) Zygotene
Explanation: During zygotene, homologous chromosomes pair through the synaptonemal complex. Defects in this complex prevent proper synapsis, leading to meiotic arrest or aneuploidy. Anaphase and telophase stages involve chromosome segregation and do not require synaptonemal formation. Therefore, A is correct, highlighting the essential role of zygotene in homolog pairing during meiosis.
4) Terminalization of chiasmata occurs in–
A) Diplotene
B) Zygotene
C) Pachytene
D) Leptotene
Answer: A) Diplotene
Explanation: Diplotene follows pachytene and is characterized by partial separation of homologs as chiasmata move toward the chromosome ends (terminalization). Zygotene involves synapsis; pachytene involves crossing over; leptotene shows early condensation. Thus, A is correct. Diplotene is also prolonged in oocytes, remaining arrested until ovulation, making this stage clinically significant.
5) Oocytes in a newborn female are arrested in which stage?
A) Pachytene
B) Diplotene
C) Metaphase II
D) Anaphase I
Answer: B) Diplotene
Explanation: Primary oocytes arrest in prophase I at the diplotene (dictyotene) stage until puberty. Pachytene and earlier phases are completed embryonically. Metaphase II occurs after ovulation. Thus, B is correct. Understanding this arrest is key in reproductive physiology and disorders involving oocyte maturation.
6) A patient with infertility shows failure of homologous chromosomes to separate in meiosis I. This is termed–
A) Non-disjunction
B) Aneuploidy correction
C) Synapsis
D) Terminalization
Answer: A) Non-disjunction
Explanation: Non-disjunction is the failure of homologous chromosomes to separate during anaphase I or sister chromatids in anaphase II, leading to aneuploid gametes. Synapsis and terminalization occur earlier in prophase I. Thus, A is correct. Non-disjunction underlies disorders such as Down, Edwards, and Patau syndromes.
7) Synapsis occurs during–
A) Diplotene
B) Zygotene
C) Anaphase I
D) Telophase II
Answer: B) Zygotene
Explanation: Zygotene is defined by the pairing (synapsis) of homologous chromosomes through the synaptonemal complex. Diplotene shows separation, while anaphase and telophase involve chromatid movement and nuclear reformation. Thus, B is correct, highlighting critical initial alignment of homologs in meiosis.
8) Which stage immediately follows pachytene?
A) Leptotene
B) Diplotene
C) Zygotene
D) Diakinesis
Answer: B) Diplotene
Explanation: The sequence of prophase I is leptotene → zygotene → pachytene → diplotene → diakinesis. Thus, diplotene follows pachytene. This distinguishes the progressive structural changes in chromosome morphology essential for successful meiosis. Therefore, B is correct.
9) A woman undergoing assisted reproduction has secondary oocytes arrested in–
A) Prophase I
B) Metaphase II
C) Anaphase I
D) Telophase I
Answer: B) Metaphase II
Explanation: Secondary oocytes arrest in metaphase II until fertilization. Prophase I arrest occurs in primary oocytes. Anaphase and telophase follow metaphase only after activation. Hence, B is correct. This arrest mechanism ensures proper timing of meiotic completion during fertilization.
10) Which phase shows maximum chromosomal condensation before meiosis I ends?
A) Zygotene
B) Pachytene
C) Diakinesis
D) Diplotene
Answer: C) Diakinesis
Explanation: Diakinesis marks the final stage of prophase I with maximal condensation of chromosomes, nuclear envelope breakdown, and spindle attachment preparation. Other stages show partial condensation. Thus, C is correct, highlighting the transition into metaphase I.
11) Failure of crossing over during pachytene most likely increases risk of–
A) Balanced translocation
B) Non-disjunction
C) Polyploidy
D) Terminal deletion
Answer: B) Non-disjunction
Explanation: Crossing over stabilizes homolog pairing. Absence of recombination weakens chiasmata, increasing the risk of homologs separating improperly during anaphase I, resulting in non-disjunction. Polyploidy usually arises from cytokinesis failure. Balanced translocations and deletions involve structural chromosomal changes not directly linked to absence of crossing over. Thus, B is correct.
Chapter: Embryology; Topic: Pharyngeal (Branchial) Apparatus; Subtopic: Nerve Derivatives of Branchial Arches
Keyword Definitions:
Branchial Arches: Mesoderm–neural crest structures forming skeletal, muscular, and neural elements of head and neck.
Second Branchial Arch (Hyoid Arch): Forms muscles of facial expression, stapes, styloid process, and is supplied by facial nerve.
Facial Nerve (VII): Nerve of the second arch, supplying muscles of facial expression.
First Branchial Arch: Forms muscles of mastication; nerve is mandibular division of trigeminal (V3).
Third Branchial Arch: Gives stylopharyngeus muscle; nerve is glossopharyngeal (IX).
1) Lead Question – 2016
Facial nerve is a derivative of which of the following branchial arch?
A) First arch
B) Second arch
C) Third arch
D) Fourth arch
Answer: B) Second arch
Explanation: The facial nerve (cranial nerve VII) is the nerve of the second branchial (hyoid) arch. This arch forms muscles of facial expression, stapedius, stylohyoid, and posterior belly of digastric. The first arch gives rise to muscles of mastication supplied by V3, the third arch is supplied by glossopharyngeal nerve (IX), and the fourth arch receives vagus nerve branches. Thus, B is correct. Recognizing nerve–arch associations is crucial in understanding congenital anomalies, branchial defects, and cranial nerve palsies affecting facial muscle function.
2) The muscle of facial expression develops from the–
A) First arch
B) Second arch
C) Third arch
D) Fourth arch
Answer: B) Second arch
Explanation: Muscles of facial expression (orbicularis oculi, orbicularis oris, buccinator, etc.) originate from the mesoderm of the second branchial arch, innervated by facial nerve (VII). The first arch forms muscles of mastication, the third gives stylopharyngeus, and the fourth gives pharyngeal constrictors. Hence, B is correct and highlights the strong link between arch derivatives and cranial nerve supply.
3) A newborn presents with facial paralysis due to absent facial nerve. Which skeletal structure is also likely affected?
A) Meckel’s cartilage
B) Stapes
C) Thyroid cartilage
D) Greater horn of hyoid
Answer: B) Stapes
Explanation: The stapes is derived from Reichert’s cartilage of the second arch, the same arch supplying facial nerve. Meckel’s cartilage (first arch) forms malleus and incus; thyroid cartilage derives from fourth arch; greater horn of hyoid from third arch. Thus, B is correct. Damage to second arch derivatives frequently co-occurs with facial nerve abnormalities.
4) The second branchial arch contributes to which muscle?
A) Tensor tympani
B) Stapedius
C) Stylopharyngeus
D) Cricothyroid
Answer: B) Stapedius
Explanation: Stapedius is a derivative of the second arch and is supplied by facial nerve. Tensor tympani comes from first arch; stylopharyngeus from third; cricothyroid from fourth arch. Thus, B is correct, reinforcing the facial nerve’s association with second arch musculature.
5) Which cranial nerve supplies derivatives of the third arch?
A) V3
B) VII
C) IX
D) X
Answer: C) IX
Explanation: Glossopharyngeal nerve (IX) supplies stylopharyngeus, the only muscle derived from the third arch. V3 supplies first arch, VII supplies second arch, and X supplies fourth and sixth arches. Thus, C is correct, demonstrating the specific nerve–arch relationships.
6) Which of the following cartilaginous structures is derived from the second arch?
A) Malleus
B) Styloid process
C) Thyroid cartilage
D) Cricoid cartilage
Answer: B) Styloid process
Explanation: The styloid process arises from Reichert’s cartilage of the second arch. Malleus is first arch; thyroid and cricoid cartilages arise from fourth and sixth arches. Thus, B is correct. This supports identifying skeletal derivatives specific to each branchial arch.
7) A neonate with dysphagia and absent gag reflex likely has abnormal development of which arch?
A) First
B) Second
C) Third
D) Fourth
Answer: C) Third
Explanation: The glossopharyngeal nerve (IX), nerve of the third arch, mediates gag reflex and supplies stylopharyngeus, essential for swallowing. First and second arch defects impair mastication and facial expression, respectively. Fourth arch defects affect pharyngeal constrictors and laryngeal muscles. Thus, C is correct, as third arch anomalies present with pharyngeal dysfunction.
8) Posterior belly of digastric muscle is derived from–
A) First arch
B) Second arch
C) Third arch
D) Fourth arch
Answer: B) Second arch
Explanation: The posterior belly of digastric originates from the second arch, supplied by facial nerve. The anterior belly is from the first arch. Third and fourth arches do not contribute to digastric muscle. Thus, B is correct, illustrating dual arch origins of this muscle.
9) The recurrent laryngeal nerve is associated with which branchial arch?
A) First
B) Second
C) Third
D) Sixth
Answer: D) Sixth
Explanation: The recurrent laryngeal nerve supplies derivatives of the sixth arch, including intrinsic laryngeal muscles except cricothyroid. First arch is V3, second arch is VII, third is IX. Thus, D is correct, showing the neural association with laryngeal development.
10) Which artery is derived from the second arch?
A) Maxillary artery
B) Stapedial artery
C) Common carotid
D) Arch of aorta
Answer: B) Stapedial artery
Explanation: The stapedial artery transiently arises from the second arch before regressing. Maxillary artery is first arch; common carotid comes from third; aortic arch from fourth. Thus, B is correct, describing vascular derivatives of the second arch.
11) A child presents with facial muscle weakness and malformed auricle. The defect likely involves–
A) First arch
B) Second arch
C) Third arch
D) Sixth arch
Answer: B) Second arch
Explanation: Second arch abnormalities lead to facial nerve dysfunction and external ear deformities because auricular hillocks arise from first and second arches. Third and sixth arches do not contribute directly to facial muscles or auricle development. Thus, B is correct, as second arch maldevelopment best explains both clinical findings.
Chapter: Embryology; Topic: Development of Kidney; Subtopic: Origin of Metanephric Structures
Keyword Definitions:
Metanephros: Definitive kidney appearing in the 5th week; forms nephron structures (kidney parenchyma).
Ureteric Bud: Outgrowth from mesonephric duct forming collecting system (ureter, pelvis, calyces, collecting ducts).
Mesonephros: Temporary embryonic kidney functioning briefly before degeneration.
Paramesonephric Duct: Müllerian duct forming female reproductive tract structures.
Metanephric Blastema: Mesenchyme induced by ureteric bud to form nephrons.
1) Lead Question – 2016
Kidney parenchyma is derived from–
A) Ureteric bud
B) Mesonephros
C) Metanephros
D) Paramesonephros
Answer: C) Metanephros
Explanation: The kidney parenchyma, including nephrons (glomeruli, proximal tubules, loops of Henle, and distal tubules), is derived from the metanephros, which develops from metanephric mesenchyme. The ureteric bud forms the collecting system only. The mesonephros functions transiently in early fetal life, while paramesonephric ducts give rise to female reproductive organs. Thus, the definitive renal tissue forming the functional filtration units originates from the metanephros, making option C the correct answer.
2) The collecting ducts of the kidney are derived from–
A) Metanephric blastema
B) Mesonephric duct
C) Ureteric bud
D) Paramesonephric duct
Answer: C) Ureteric bud
Explanation: The ureteric bud gives rise to ureter, renal pelvis, major and minor calyces, and collecting ducts. Metanephric blastema forms nephron components. The mesonephric duct forms male reproductive structures, and paramesonephric duct forms female reproductive organs. Thus, C is correct, reflecting the branching morphogenesis essential for forming the collecting system.
3) A newborn with renal agenesis likely has developmental failure of the–
A) Metanephric mesenchyme
B) Paramesonephric duct
C) Cloacal membrane
D) Surface ectoderm
Answer: A) Metanephric mesenchyme
Explanation: Renal agenesis occurs when the ureteric bud fails to induce the metanephric mesenchyme, preventing nephron formation. Paramesonephric ducts form reproductive organs; cloacal membrane forms urogenital and anal openings. Surface ectoderm does not contribute to kidney development. Therefore, A is correct, representing a failure in inductive interaction between ureteric bud and metanephric tissue.
4) Glomeruli develop from the–
A) Ureteric bud
B) Metanephric blastema
C) Mesonephric duct
D) Neural crest
Answer: B) Metanephric blastema
Explanation: Glomeruli originate from metanephric mesenchyme, which forms all nephron components except the collecting system. The ureteric bud forms collecting ducts, while mesonephric duct and neural crest are unrelated to nephron formation. Thus, B is correct, reflecting the essential role of metanephric blastema in nephron development.
5) In Potter sequence, the most direct cause of reduced amniotic fluid is–
A) Defective ureteric bud branching
B) Absent metanephric blastema induction
C) Paramesonephric duct regression
D) Urachal anomaly
Answer: B) Absent metanephric blastema induction
Explanation: Renal agenesis results from failed induction of metanephric blastema by the ureteric bud, leading to absent urine production and oligohydramnios (Potter sequence). Paramesonephric structures affect reproductive tract only; urachal anomalies affect bladder apex. Thus, B is correct, identifying the key embryologic defect behind Potter features.
6) Which structure induces metanephric mesenchyme to form nephrons?
A) Paramesonephros
B) Ureteric bud
C) Cloacal membrane
D) Cardinal veins
Answer: B) Ureteric bud
Explanation: Reciprocal induction between ureteric bud and metanephric mesenchyme is essential: the bud stimulates nephron formation, and mesenchyme induces bud branching. Paramesonephros and cloacal membrane do not contribute. Cardinal veins belong to venous development. Thus, B is correct, highlighting the critical embryologic signaling pathway.
7) Mesonephric ducts persist in males to form–
A) Epididymis, vas deferens
B) Collecting ducts
C) Nephrons
D) Urethra
Answer: A) Epididymis, vas deferens
Explanation: Mesonephric (Wolffian) ducts form epididymis, vas deferens, seminal vesicles, and ejaculatory ducts in males. They do not contribute to nephron or collecting system development. Thus, A is correct, illustrating their role in male reproductive anatomy.
8) Which fetal structure gives rise to major and minor renal calyces?
A) Ureteric bud
B) Metanephric mesenchyme
C) Mesonephros
D) Intermediate mesoderm
Answer: A) Ureteric bud
Explanation: Branching of the ureteric bud forms renal pelvis, major calyces, minor calyces, and collecting ducts. Metanephric mesenchyme forms nephron units. Mesonephros degenerates. While intermediate mesoderm gives rise to kidney precursors, the direct source is the ureteric bud. Thus, A is correct.
9) A neonate shows duplex collecting system. This most likely results from–
A) Early splitting of the ureteric bud
B) Duplicated metanephric mesenchyme
C) Paramesonephric duct fusion
D) Absent mesonephric duct
Answer: A) Early splitting of the ureteric bud
Explanation: Duplex kidneys result when the ureteric bud divides early, creating two collecting systems. Metanephric mesenchyme simply responds to bud branching; paramesonephric ducts form reproductive organs; mesonephric duct absence causes renal agenesis, not duplication. Thus, A is correct.
10) Which embryonic derivative forms the distal convoluted tubule?
A) Ureteric bud
B) Metanephric blastema
C) Mesonephric duct
D) Surface ectoderm
Answer: B) Metanephric blastema
Explanation: All nephron tubules—including proximal, loop of Henle, and distal tubules—come from metanephric blastema. The ureteric bud forms only collecting ducts. Surface ectoderm and mesonephric duct are unrelated. Thus, B is correct.
11) A fetal ultrasound shows bilateral renal cysts with preserved collecting system. This suggests a defect in–
A) Metanephric blastema differentiation
B) Ureteric bud formation
C) Cloacal partitioning
D) Paramesonephric ducts
Answer: A) Metanephric blastema differentiation
Explanation: Polycystic kidney diseases often involve defective nephron development from metanephric mesenchyme, while collecting ducts remain intact. Ureteric bud defects cause absent collecting systems. Cloacal defects affect bladder/rectum; paramesonephric ducts affect reproductive tract. Thus, A is correct, indicating nephron-level developmental pathology.
Chapter: Embryology; Topic: Development of Venous System; Subtopic: Formation of Inferior Vena Cava (IVC)
Keyword Definitions:
Vitelline veins: Paired embryonic veins that contribute to hepatic vasculature and the hepatic segment of the IVC.
Cardinal veins: Early embryonic systemic veins (anterior and posterior) largely replaced but contributing to parts of SVC and some venous channels.
Subcardinal veins: Paired veins that form portions of the renal and prerenal IVC segments and renal veins.
Supracardinal veins: Paired veins that form the postrenal (infrarenal) IVC and parts of the azygos/hemiazygos system.
Intercardinal anastomoses: Connections between cardinal veins; some form venous channels (azygos system) but not major segments of IVC.
1) Lead Question – 2016
All of the following help in formation of IVC except -
A) The posterior intercardinal anastomosis
B) Terminal portion of right vitelline vein
C) Segment of right cardinal vein
D) Subcardinal sinus
Answer: A) The posterior intercardinal anastomosis
Explanation: The IVC forms from a complex cranial–caudal series of embryonic veins: the hepatic segment from the right vitelline vein (terminal portion), the prerenal/renal segments from subcardinal veins and their anastomoses (including subcardinal–supracardinal connections), and the postrenal (infrarenal) part from the right supracardinal vein. While remnants of cardinal system contribute small channels, the posterior intercardinal anastomosis specifically helps form portions of the azygos/hemiazygos or transient connections rather than a principal IVC segment. Therefore the posterior intercardinal anastomosis (A) is **not** a contributor to the main IVC formation.
2) Which embryonic vein primarily contributes to the hepatic segment of the IVC?
A) Left vitelline vein
B) Right vitelline vein
C) Right supracardinal vein
D) Left subcardinal vein
Answer: B) Right vitelline vein
Explanation: The hepatic segment of the inferior vena cava originates from the terminal portion of the right vitelline vein after extensive remodeling within the developing liver. Vitelline veins supply the hepatic sinusoids; the right-sided vitelline structures are preserved to form the hepatic IVC and hepatic veins. Supracardinal and subcardinal veins form more caudal IVC segments; the left vitelline and left-sided subcardinal structures largely regress. Thus, the right vitelline vein (B) is the principal embryologic contributor to the hepatic segment of the adult IVC.
3) The infrarenal (postrenal) segment of the IVC is derived from–
A) Left supracardinal vein
B) Right supracardinal vein
C) Right posterior cardinal vein
D) Left subcardinal vein
Answer: B) Right supracardinal vein
Explanation: The infrarenal (postrenal) portion of IVC is derived from the right supracardinal vein. During embryogenesis the supracardinal system replaces posterior cardinal veins dorsally; the right supracardinal persists as the lower IVC while the left supracardinal mostly regresses. The posterior cardinal veins largely disappear or contribute minimally. Subcardinal veins form the prerenal/renal region rather than the infrarenal segment. Therefore, the correct embryologic source for postrenal IVC is the right supracardinal vein (B).
4) The renal segment of IVC results from anastomosis between–
A) Vitelline and posterior cardinal veins
B) Subcardinal and supracardinal veins
C) Anterior and posterior cardinal veins
D) Left and right vitelline veins
Answer: B) Subcardinal and supracardinal veins
Explanation: The renal segment of the IVC is formed by complex anastomoses between the subcardinal and supracardinal veins, specifically the subcardinal–supracardinal connection that becomes the renal portion. This anastomosis allows drainage of renal veins into the IVC. Vitelline veins form the hepatic region, while cardinal veins are earlier dorsal venous channels largely replaced. Thus, B is correct: the subcardinal–supracardinal anastomosis is essential for the renal segment development.
5) Failure of the right subcardinal system to connect properly with the hepatic (vitelline) segment would most likely cause–
A) Absent hepatic veins
B) Double IVC or abnormal left-sided IVC
C) Pulmonary venous return defect
D) Persistent left SVC
Answer: B) Double IVC or abnormal left-sided IVC
Explanation: Errors in regression or persistence of supracardinal/subcardinal channels can produce anomalous patterns, such as a double IVC (persistence of left supracardinal) or left-sided IVC when right-sided segments regress. If right subcardinal–vitelline connections fail, alternate pathways may persist leading to duplicated or transposed IVC. Pulmonary venous return and SVC anomalies involve different embryologic sources. Therefore, venous malformations like double or left-sided IVC (B) are the expected consequences of faulty subcardinal–vitelline integration.
6) Which embryonic venous channel largely regresses and is replaced by supracardinal veins dorsally?
A) Anterior cardinal veins
B) Posterior cardinal veins
C) Vitelline veins
D) Umbilical veins
Answer: B) Posterior cardinal veins
Explanation: Posterior cardinal veins are early dorsal embryonic channels that largely regress as the supracardinal system develops dorsally and takes over the role of posterior body wall drainage. Portions of posterior cardinals contribute transiently or to small remnants, but the supracardinal veins form the definitive infrarenal IVC and azygos system. Vitelline veins persist in hepatic region; anterior cardinals form SVC. Thus, posterior cardinal veins (B) are principally replaced by supracardinal vessels.
7) The hepatic veins drain into the IVC segment derived from–
A) Right supracardinal vein
B) Right vitelline vein (terminal portion)
C) Left subcardinal vein
D) Posterior cardinal vein
Answer: B) Right vitelline vein (terminal portion)
Explanation: Hepatic veins drain into the hepatic segment of the IVC, which is derived from the terminal portion of the right vitelline vein incorporated into the liver sinusoids. This vitelline-derived segment connects the liver venous outflow to the rest of the IVC. Supracardinal/subcardinal regions form caudal segments; posterior cardinals largely regress. Therefore, the correct embryologic origin for the hepatic IVC receiving hepatic veins is the terminal right vitelline vein (B).
8) Persistent left-sided supracardinal vein results in–
A) Retroaortic left renal vein or duplicated IVC
B) Agenesis of IVC
C) Persistent ductus venosus
D) Interrupted aortic arch
Answer: A) Retroaortic left renal vein or duplicated IVC
Explanation: Persistence of left supracardinal structures can produce a duplicated IVC (with both right and left infrarenal IVCs) or a retroaortic left renal vein if the left-sided channel persists abnormally. Complete agenesis of IVC is rare and involves other failures. Ductus venosus and aortic arch defects have different embryological bases. Hence, A correctly describes typical anomalies arising from persistence of left supracardinal venous channels.
9) The terminal hepatic segment of IVC is lost in which anomaly leading to azygos continuation of IVC?
A) Failure of right vitelline formation
B) Failure of right subcardinal–hepatic anastomosis (hepatic segment absent)
C) Persistence of posterior cardinal veins
D) Duplication of ureteric bud
Answer: B) Failure of right subcardinal–hepatic anastomosis (hepatic segment absent)
Explanation: Azygos continuation of the IVC occurs when the hepatic segment (terminal connection to the heart) fails to form—commonly due to absent right subcardinal–hepatic anastomosis—forcing systemic venous return from the lower body to reach the SVC via the azygos system (supracardinal remnants). This anomaly is not due to vitelline failure per se; it reflects disrupted subcardinal–vitelline integration. Therefore B accurately describes the embryologic defect producing azygos continuation of IVC.
10) Which embryonic vein contributes to formation of the renal veins?
A) Vitelline veins
B) Subcardinal veins
C) Anterior cardinal veins
D) Umbilical veins
Answer: B) Subcardinal veins
Explanation: The subcardinal veins develop medial to the mesonephros and form important components of the prerenal and renal IVC segments; they also give rise to the renal veins. Subcardinal–supracardinal anastomoses position the renal veins into the IVC. Vitelline veins contribute to hepatic veins, anterior cardinals to SVC, and umbilical veins to the fetal placental circuit. Thus, B is correct: subcardinal veins are vital for renal venous development.
11) Clinically, a duplicated IVC results from persistence of which embryologic structure on the left side?
A) Left vitelline vein
B) Left supracardinal vein
C) Left subcardinal vein only
D) Posterior intercardinal anastomosis
Answer: B) Left supracardinal vein
Explanation: A duplicated IVC typically arises when the left supracardinal vein fails to regress while the right supracardinal also persists, producing two infrarenal venous channels (right and left IVC). This venous duplication may be asymptomatic but is important surgically and radiologically. Left supracardinal persistence explains the anomaly more specifically than subcardinal or vitelline persistence. Posterior intercardinal anastomosis is not responsible for a true duplicated IVC. Therefore, B is the correct embryologic cause of duplicated IVC.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Derivatives of Urogenital Sinus
Keyword Definitions:
Urogenital Sinus: Endodermal structure forming bladder, female urethra, and lower vagina.
Mesonephric Duct: Gives rise to male reproductive ducts but regresses in females.
Ureteric Bud: Outgrowth forming ureter, pelvis, calyces, and collecting ducts.
Metanephric Blastema: Mesenchyme forming nephrons.
Endoderm-derived Epithelium: Lines bladder and female urethra.
1) Lead Question – 2016
Female urethra develops from–
A) Urogenital sinus
B) Mesonephric duct
C) Ureteric bud
D) Metanephric blastema
Answer: A) Urogenital sinus
Explanation: The female urethra arises from the pelvic part of the urogenital sinus, which is derived from endoderm. The mesonephric duct largely regresses in females, forming no part of the urethra. The ureteric bud forms upper urinary tract structures such as ureter and collecting ducts, while the metanephric blastema forms nephrons. Thus, A is correct. Understanding the embryological origin of the urethra is essential in explaining congenital conditions such as urethral anomalies and their association with urogenital sinus maldevelopment.
2) The urinary bladder epithelium is derived from–
A) Endoderm
B) Mesoderm
C) Ectoderm
D) Neural crest
Answer: A) Endoderm
Explanation: The bladder’s lining develops from the endodermal urogenital sinus. Only the trigone region has mesodermal origin due to mesonephric duct incorporation. Ectoderm and neural crest do not contribute to bladder epithelium. Thus, A is correct. This developmental distinction explains transitional epithelium origin and why certain congenital anomalies arise from urogenital sinus defects.
3) A newborn girl presents with urethral atresia. The defect most likely occurred in the–
A) Urogenital sinus
B) Mesonephric duct
C) Ureteric bud
D) Cloacal membrane
Answer: A) Urogenital sinus
Explanation: The female urethra forms entirely from the urogenital sinus. Atresia suggests failed canalization or development of this structure. The mesonephric duct regresses in females, the ureteric bud forms upper tract structures, and the cloacal membrane ruptures to form anal and urogenital openings but does not form the urethra itself. Thus, A is correct, linking urethral anomalies to sinus maldevelopment.
4) In males, the prostatic urethra develops from–
A) Mesonephric duct
B) Urogenital sinus
C) Surface ectoderm
D) Cloacal membrane
Answer: B) Urogenital sinus
Explanation: The prostatic urethra arises from the pelvic part of the urogenital sinus in males, similar to the female urethra. Mesonephric ducts contribute ejaculatory ducts, not urethra. Surface ectoderm forms external genitalia. Thus, B is correct. This shared origin explains similarities in epithelial lining and congenital anomalies involving urethral development.
5) The mesonephric duct in females forms–
A) Urethra
B) Gartner duct remnants
C) Bladder trigone
D) Upper vagina
Answer: B) Gartner duct remnants
Explanation: Mesonephric ducts regress in females, leaving Gartner duct remnants along the lateral vaginal wall. They do not form urethra or upper vagina. The trigone is formed by mesonephric duct incorporation but its epithelium becomes endodermal. Thus, B is correct. Gartner duct cysts may arise clinically from these remnants.
6) The ureter develops from the–
A) Urogenital sinus
B) Mesonephric duct
C) Ureteric bud
D) Metanephric blastema
Answer: C) Ureteric bud
Explanation: The ureteric bud gives rise to ureter, renal pelvis, calyces, and collecting ducts. The urogenital sinus forms bladder and urethra. The metanephric blastema forms nephrons. Thus, C is correct. Abnormal budding can lead to duplication anomalies and congenital hydronephrosis.
7) A neonate has bilateral renal agenesis. The defect is most likely in–
A) Ureteric bud
B) Urogenital sinus
C) Cloacal membrane
D) Mesonephric duct regression
Answer: A) Ureteric bud
Explanation: Renal agenesis results from failure of ureteric bud to interact with the metanephric blastema. The urogenital sinus forms bladder and urethra, not kidneys. Cloacal membrane defects affect openings, not kidney formation. Mesonephric duct regression is normal in females. Thus, A is correct. Lack of induction prevents nephron formation, leading to oligohydramnios and Potter sequence.
8) The lower part of the vagina is derived from–
A) Urogenital sinus
B) Paramesonephric ducts
C) Cloacal membrane
D) Mesoderm
Answer: A) Urogenital sinus
Explanation: The lower vagina originates from the sinovaginal bulbs of the urogenital sinus. Upper vagina forms from paramesonephric ducts. Cloacal membrane forms external openings only. Thus, A is correct. Failure of fusion or canalization can cause vaginal atresia or septation.
9) The bladder trigone region is derived from–
A) Mesonephric duct
B) Urogenital sinus
C) Surface ectoderm
D) Ureteric bud
Answer: A) Mesonephric duct
Explanation: The trigone initially forms from mesoderm of the mesonephric ducts but is later overgrown by endodermal epithelium from the urogenital sinus. Ureteric bud forms upper urinary tract, and ectoderm does not contribute. Thus, A is correct. This dual origin explains unique trigonal anatomy.
10) Which structure forms nephrons?
A) Mesonephric duct
B) Ureteric bud
C) Metanephric blastema
D) Urogenital sinus
Answer: C) Metanephric blastema
Explanation: Nephrons—including glomeruli and tubules—develop from metanephric blastema. The ureteric bud forms collecting ducts; mesonephric duct forms male reproductive ducts; urogenital sinus forms bladder and urethra. Thus, C is correct. Proper interaction between blastema and ureteric bud is vital for kidney morphogenesis.
11) A female infant with urogenital sinus malformation may present with–
A) Common opening for urethra and vagina
B) Absent kidney
C) Imperforate anus
D) Enlarged clitoris only
Answer: A) Common opening for urethra and vagina
Explanation: Urogenital sinus anomalies can lead to a persistent common channel for urethra and vagina due to incomplete separation. Kidney agenesis results from ureteric bud defects, not urogenital sinus issues. Imperforate anus involves cloacal membrane. Thus, A is correct. These anomalies often require surgical correction due to functional and developmental concerns.
Chapter: Embryology; Topic: Development of Brain; Subtopic: Formation of Commissural Structures
Keyword Definitions:
Lamina Terminalis: Region at the rostral end of neural tube from which commissures, including corpus callosum, develop.
Corpus Callosum: Largest commissural fiber bundle connecting cerebral hemispheres.
Basal Plate: Ventral neural tube region forming motor nuclei.
Alar Plate: Dorsal neural tube region forming sensory nuclei.
Commissures: Fiber tracts connecting corresponding cortical areas across hemispheres.
1) Lead Question – 2016
Part of neural tube from which corpus callosum develops:
A) Basal lamina
B) Alar lamina
C) Lamina terminalis
D) Basal plate
Answer: C) Lamina terminalis
Explanation: The corpus callosum develops from the lamina terminalis, located at the rostral end of the neural tube. It forms the major commissural pathway connecting the cerebral hemispheres. The basal plate gives rise to motor nuclei, and the alar plate forms sensory nuclei, neither contributing to commissural fiber formation. The lamina terminalis serves as the primitive anterior wall of the third ventricle and is crucial for the formation of major forebrain commissures. Therefore, C is correct, reflecting the specific origin of interhemispheric connectivity in brain development.
2) The anterior commissure develops from the region near the–
A) Lamina terminalis
B) Basal plate
C) Alar plate
D) Pontine flexure
Answer: A) Lamina terminalis
Explanation: The anterior commissure, like the corpus callosum, forms in association with the lamina terminalis at the rostral neural tube. Basal and alar plates form motor and sensory nuclei, respectively, and the pontine flexure contributes to hindbrain shaping. Thus, A is correct. This commissure connects olfactory structures and parts of the temporal lobes, highlighting the lamina terminalis as the central site for forebrain commissural formation.
3) A newborn with agenesis of corpus callosum most likely has a developmental defect in the–
A) Lamina terminalis
B) Neural crest
C) Basal plate
D) Otic placode
Answer: A) Lamina terminalis
Explanation: Agenesis of the corpus callosum results from failed development of commissural fibers across the lamina terminalis. Neural crest defects produce craniofacial and autonomic abnormalities, whereas basal plate defects affect motor nuclei, and otic placode forms the inner ear. Thus, A is correct. Absence of interhemispheric fibers may lead to developmental delays, seizures, or be asymptomatic depending on compensatory pathways.
4) The basal plate gives rise to–
A) Motor nuclei
B) Sensory nuclei
C) Commissural fibers
D) Cerebellar cortex
Answer: A) Motor nuclei
Explanation: The basal plate of the neural tube forms motor neurons and motor cranial nerve nuclei. Sensory nuclei arise from the alar plate, commissural fibers from the lamina terminalis, and cerebellar cortex from the rhombic lip. Thus, A is correct. This organization explains the ventral motor and dorsal sensory arrangement of the spinal cord and brainstem, essential for neuroanatomical localization.
5) A child with defective sensory nuclei formation likely has an abnormality in the–
A) Alar plate
B) Basal lamina
C) Mesoderm
D) Hypothalamus
Answer: A) Alar plate
Explanation: The alar plate forms sensory nuclei in the spinal cord and brainstem. Basal plate forms motor structures, mesoderm forms connective and muscular tissues, and hypothalamus develops from diencephalic neuroectoderm. Thus, A is correct. Defects lead to impaired sensory processing and clinical symptoms such as reduced pain, touch, or proprioceptive abilities.
6) Which structure is derived from the diencephalon?
A) Thalamus
B) Pons
C) Cerebellum
D) Medulla
Answer: A) Thalamus
Explanation: The thalamus arises from the diencephalon, which also forms hypothalamus and epithalamus. Pons and medulla derive from hindbrain (metencephalon and myelencephalon), and cerebellum from the rhombic lip. Thus, A is correct. The diencephalon’s development is important for sensory relay and autonomic regulation, central to neurological function.
7) A newborn with holoprosencephaly likely has defective development of the–
A) Prosencephalon
B) Metencephalon
C) Myelencephalon
D) Neural crest
Answer: A) Prosencephalon
Explanation: Holoprosencephaly results from failure of prosencephalon to divide into two hemispheres. Metencephalon forms pons and cerebellum; myelencephalon forms medulla; neural crest forms peripheral structures. Thus, A is correct. This condition ranges from mild midline defects to severe craniofacial abnormalities, often associated with genetic and environmental factors.
8) The pineal gland develops from–
A) Telencephalon
B) Diencephalon
C) Mesencephalon
D) Neural crest
Answer: B) Diencephalon
Explanation: The pineal gland arises from the roof of the diencephalon, alongside structures such as the epithalamus. Telencephalon forms cerebral hemispheres, mesencephalon forms midbrain, and neural crest forms connective tissues and ganglia. Thus, B is correct. The pineal gland regulates melatonin secretion and circadian rhythms, demonstrating its neuroendocrine role.
9) Posterior pituitary gland originates from–
A) Rathke’s pouch
B) Infundibulum
C) Neural crest
D) Surface ectoderm
Answer: B) Infundibulum
Explanation: The posterior pituitary (neurohypophysis) forms from neuroectoderm of the diencephalic infundibulum. Rathke’s pouch forms the anterior pituitary. Neural crest and surface ectoderm do not form these structures. Thus, B is correct. This explains how posterior pituitary stores and releases hypothalamic hormones such as ADH and oxytocin.
10) A neonate has facial anomalies and outflow tract defects. The embryological cause likely involves–
A) Neural crest migration
B) Lamina terminalis
C) Rathke’s pouch
D) Notochord
Answer: A) Neural crest migration
Explanation: Neural crest cells contribute to craniofacial structures and cardiac outflow tracts. Defects cause syndromes like DiGeorge and craniofacial dysostosis. Lamina terminalis forms commissures, Rathke’s pouch forms anterior pituitary, and notochord induces neural tube but does not form these structures. Thus, A is correct. Migration failures result in combined craniofacial and cardiac anomalies.
11) The cerebral hemispheres arise from the–
A) Telencephalon
B) Diencephalon
C) Mesencephalon
D) Myelencephalon
Answer: A) Telencephalon
Explanation: The telencephalon forms cerebral hemispheres, basal ganglia, and olfactory bulbs. Diencephalon forms thalamus and hypothalamus, mesencephalon forms midbrain, and myelencephalon forms medulla. Thus, A is correct. Proper development is essential for cognition, coordination, and higher neurological functions.
Chapter: Embryology; Topic: Pharyngeal Apparatus; Subtopic: Third & Fourth Pharyngeal Pouch Anomalies – DiGeorge Syndrome
Keyword Definitions:
Pharyngeal Pouches: Endoderm-lined sacs giving rise to thymus, parathyroids, and other neck structures.
DiGeorge Syndrome: Developmental disorder due to failure of third and fourth pouch formation.
Thymic Hypoplasia: Underdeveloped thymus leading to T-cell immunodeficiency.
Hypocalcemia: Low calcium from absent/inadequate parathyroid glands.
22q11 Deletion: Chromosomal microdeletion associated with DiGeorge syndrome.
1) Lead Question – 2016
DiGeorge syndrome is characterized by all except?
A) Congenital thymic hypoplasia
B) Abnormal development of third and fourth pouches
C) Hypothyroidism
D) Hypocalcemic tetany
Answer: C) Hypothyroidism
Explanation: DiGeorge syndrome results from defective development of the third and fourth pharyngeal pouches, causing thymic hypoplasia and absent or hypoplastic parathyroid glands. This leads to T-cell immunodeficiency and hypocalcemic tetany. Hypothyroidism is not a typical feature because the thyroid gland develops from a midline endodermal diverticulum, not from the pharyngeal pouches affected in DiGeorge syndrome. Therefore, the correct answer is C. Understanding pouch derivatives helps identify associated clinical defects including immune deficiency, hypocalcemia, cardiac anomalies, and craniofacial abnormalities.
2) The thymus primarily develops from which pharyngeal pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: C) Third
Explanation: The thymus arises from the ventral wing of the third pharyngeal pouch, which also contributes to the inferior parathyroid glands. The first pouch forms the middle ear and auditory tube, while the second forms tonsillar epithelium. The fourth pouch forms superior parathyroids. Thus, C is correct. Failure of the third pouch produces thymic hypoplasia seen in DiGeorge syndrome, resulting in T-cell immunodeficiency and recurrent infections.
3) A newborn with DiGeorge syndrome is most likely to have which endocrine abnormality?
A) Hyperparathyroidism
B) Hypocalcemia
C) Cortisol deficiency
D) Hyperthyroidism
Answer: B) Hypocalcemia
Explanation: Hypocalcemia arises due to absent or hypoplastic parathyroid glands derived from the third and fourth pharyngeal pouches. Hyperparathyroidism does not occur because the glands are underdeveloped. Cortisol deficiency involves adrenal defects, unrelated to pharyngeal pouches. Thyroid disorders are not typical in DiGeorge syndrome. Thus, B is correct. The resulting low calcium levels can cause tetany or seizures in neonates, making recognition clinically important.
4) Which cardiac defect is frequently associated with DiGeorge syndrome?
A) Atrial septal defect
B) Tetralogy of Fallot
C) Patent ductus arteriosus
D) Coarctation of aorta
Answer: B) Tetralogy of Fallot
Explanation: DiGeorge syndrome often presents with conotruncal cardiac anomalies such as tetralogy of Fallot, truncus arteriosus, and interrupted aortic arch. These arise from abnormal neural crest cell migration affecting outflow tract development. ASD and PDA occur in many conditions but are not characteristic associations. Thus, B is correct. Defective neural crest development ties together cardiac, craniofacial, and thymic abnormalities seen clinically.
5) The inferior parathyroid glands develop from which pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: C) Third
Explanation: The third pharyngeal pouch gives rise to the thymus (ventral wing) and inferior parathyroid glands (dorsal wing). The fourth pouch gives rise to the superior parathyroids. The first and second pouches form ear and tonsillar structures. Thus, C is correct. DiGeorge syndrome involving failed development of the third pouch therefore produces hypocalcemia due to missing inferior parathyroids.
6) A child with recurrent viral infections and absent T-cells likely has underdevelopment of–
A) Parathyroid glands
B) Thymus
C) Thyroid gland
D) Adrenal cortex
Answer: B) Thymus
Explanation: The thymus is essential for T-cell maturation. In DiGeorge syndrome, thymic hypoplasia leads to profound T-cell deficiency, causing recurrent viral and fungal infections. Parathyroid defects cause hypocalcemia, not immune deficiency. Thyroid and adrenal cortex do not significantly influence T-cell maturation. Thus, B is correct. Thymic aplasia is a hallmark feature of third pouch developmental disorders.
7) The superior parathyroid glands are derivatives of which pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: D) Fourth
Explanation: The superior parathyroids arise from the dorsal wing of the fourth pharyngeal pouch, while the inferior parathyroids develop from the third. This positional reversal reflects migration patterns. The first pouch forms auditory structures and the second forms tonsillar tissues. Thus, D is correct. Defects in fourth pouch development contribute to hypocalcemia seen in DiGeorge syndrome.
8) A patient with DiGeorge syndrome may present with which craniofacial feature?
A) Macroglossia
B) Cleft palate
C) Microtia
D) Hemifacial microsomia
Answer: B) Cleft palate
Explanation: Cleft palate commonly occurs in DiGeorge syndrome due to defective neural crest migration affecting facial development. Macroglossia is seen in Beckwith–Wiedemann syndrome; microtia in first arch defects; hemifacial microsomia in Goldenhar syndrome. Thus, B is correct. Craniofacial abnormalities often accompany immune and cardiac defects in this condition, reflecting shared developmental pathways.
9) Hypocalcemic tetany in DiGeorge syndrome is due to absence of–
A) Superior parathyroids
B) Inferior parathyroids
C) Both superior and inferior parathyroids
D) Thyroid follicular cells
Answer: C) Both superior and inferior parathyroids
Explanation: Although classically associated with inferior parathyroid agenesis, DiGeorge syndrome may involve defective development of both third and fourth pouches, causing loss of both sets of parathyroids. Thyroid follicular cells arise from endoderm and are unaffected. Thus, C is correct. Severe hypocalcemia can manifest as muscle spasms, laryngospasm, or seizures, requiring prompt correction.
10) Which chromosomal deletion is most commonly associated with DiGeorge syndrome?
A) 7q11 deletion
B) 22q11 deletion
C) 5p deletion
D) 15q11 deletion
Answer: B) 22q11 deletion
Explanation: The 22q11 microdeletion disrupts TBX1 gene expression, impairing neural crest migration and pharyngeal pouch development. 7q11 deletion causes Williams syndrome; 5p deletion causes Cri-du-chat; 15q11 abnormalities involve Prader–Willi and Angelman syndromes. Thus, B is correct. The 22q11 deletion explains the multi-system presentation of DiGeorge syndrome, including cardiac, immune, facial, and endocrine abnormalities.
11) A neonate with DiGeorge syndrome is most likely to show–
A) Elevated T-cell count
B) Low serum calcium
C) Elevated thyroid hormones
D) High cortisol
Answer: B) Low serum calcium
Explanation: Low serum calcium reflects absent or hypoplastic parathyroid glands derived from third and fourth pharyngeal pouches. T-cells are typically reduced, not elevated. Thyroid and adrenal hormones are generally normal. Thus, B is correct. Early recognition of hypocalcemia is critical as it may present with tetany or seizures in affected neonates.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of Optic Vesicle
Keyword Definitions:
Optic Vesicle: Lateral outgrowth from forebrain neuroectoderm forming major ocular structures.
Neuroectoderm: Embryonic tissue giving rise to retina, optic nerve, and optic stalk.
Surface Ectoderm: Forms lens, corneal epithelium, and eyelid structures.
Mesoderm: Contributes to extraocular muscles and some vascular components.
Neural Crest Cells: Form corneal stroma, sclera, and choroid.
1) Lead Question – 2016
Optic vesicle is derived from–
A) Endoderm
B) Mesoderm
C) Neuroectoderm
D) Surface ectoderm
Answer: C) Neuroectoderm
Explanation: The optic vesicle develops as a lateral evagination of the forebrain neuroectoderm. It later forms the optic cup, which gives rise to the neural and pigmented layers of the retina. Surface ectoderm forms the lens, while mesoderm contributes to vascular and muscular structures around the eye. Endoderm does not participate in ocular formation. Therefore, the correct answer is C. Neuroectodermal origin explains the similarity between the retina and central nervous system tissues and underlies ocular disorders linked to neural developmental defects.
2) The lens of the eye is derived from–
A) Neuroectoderm
B) Surface ectoderm
C) Mesoderm
D) Endoderm
Answer: B) Surface ectoderm
Explanation: The lens originates from surface ectoderm after induction by the underlying optic vesicle. Neuroectoderm forms the retina and optic nerve, mesoderm contributes vascular tissues, and endoderm plays no role in eye formation. Thus, B is correct. This developmental interaction highlights the importance of inductive signaling between neural and ectodermal tissues, essential for normal lens development and preventing congenital anomalies such as aphakia.
3) A newborn presents with congenital absence of the retina. The embryological defect most likely involves failure of development of the–
A) Optic cup
B) Lens placode
C) Mesoderm
D) Neural crest cells
Answer: A) Optic cup
Explanation: The optic cup is derived from neuroectoderm and forms both layers of the retina. Failure of its development leads to retinal agenesis. Lens placode generates the lens, mesoderm contributes extraocular muscles, and neural crest forms corneal stroma and sclera. Thus, A is correct. Understanding this helps clinicians evaluate ocular malformations and recognize primary defects in neural tissue rather than accessory ocular structures.
4) The corneal epithelium is derived from–
A) Surface ectoderm
B) Mesoderm
C) Neural crest
D) Neuroectoderm
Answer: A) Surface ectoderm
Explanation: The corneal epithelium forms from surface ectoderm, similar to the lens and conjunctiva. Mesoderm does not form epithelium, neural crest forms corneal stroma and endothelium, and neuroectoderm forms retina. Thus, A is correct. This explains why corneal epithelial disorders behave like ectodermal defects and differ from stromal conditions involving neural crest abnormalities.
5) A child presents with hypoplasia of the optic nerve. This structure is derived from–
A) Surface ectoderm
B) Mesoderm
C) Neuroectoderm
D) Endoderm
Answer: C) Neuroectoderm
Explanation: The optic nerve arises from axons of retinal ganglion cells, which originate from neuroectoderm. Mesoderm forms surrounding connective tissues, surface ectoderm forms the lens, and endoderm does not contribute to ocular structures. Thus, C is correct. Optic nerve defects therefore reflect central nervous system–related developmental anomalies rather than surface or mesodermal abnormalities.
6) The choroid and sclera primarily develop from–
A) Neural crest cells
B) Surface ectoderm
C) Endoderm
D) Neuroectoderm
Answer: A) Neural crest cells
Explanation: Neural crest contributes extensively to connective tissue structures of the eye including sclera, choroid, and corneal stroma. Neuroectoderm forms retina and optic nerve, surface ectoderm forms lens and corneal epithelium, and endoderm has no ocular role. Thus, A is correct. Maldevelopment of neural crest leads to anterior segment dysgenesis, highlighting the importance of these migratory cells.
7) A neonate with aniridia likely has a defect in development of the–
A) Optic vesicle
B) Surface ectoderm
C) Neural crest migration
D) Mesodermal condensation
Answer: A) Optic vesicle
Explanation: The iris stroma and muscles originate from the optic cup, an extension of the optic vesicle. Deficiency in its development can cause aniridia. Neural crest forms supporting stromal tissues but not the iris muscles themselves. Surface ectoderm forms lens, not iris, and mesoderm contributes minimally. Thus, A is correct. Aniridia often accompanies PAX6 gene defects, demonstrating the close linkage between optic vesicle development and ocular patterning.
8) The retinal pigment epithelium develops from–
A) Neural crest
B) Surface ectoderm
C) Neuroectoderm
D) Mesoderm
Answer: C) Neuroectoderm
Explanation: The RPE forms from the outer layer of the optic cup derived from neuroectoderm. Neural crest forms corneal stroma and sclera, surface ectoderm forms lens epithelium, and mesoderm supports vascular components. Thus, C is correct. RPE disorders reflect intrinsic neural developmental abnormalities rather than neural crest–related defects.
9) A congenital coloboma results from failure of closure of the–
A) Optic fissure
B) Lens pit
C) Corneal groove
D) Vitreous cavity
Answer: A) Optic fissure
Explanation: Coloboma is caused by incomplete closure of the embryonic optic fissure, a neuroectodermal defect. Lens pit abnormalities cause aphakia, corneal groove issues cause anterior chamber defects, and vitreous cavity malformations cause posterior eye abnormalities. Thus, A is correct. Colobomas can affect iris, choroid, retina, or optic nerve depending on the extent of fissure persistence.
10) The extraocular muscles arise from–
A) Neural crest cells
B) Preotic mesoderm
C) Surface ectoderm
D) Neuroectoderm
Answer: B) Preotic mesoderm
Explanation: Extraocular muscles develop from preotic mesodermal myotomes. Neural crest contributes to connective tissue coverings, surface ectoderm forms lens and cornea, and neuroectoderm forms retina and optic nerve. Thus, B is correct. These structures are essential for coordinated eye movements and their embryologic origin explains their distinct innervation by cranial nerves III, IV, and VI.
11) A baby has congenital cataract due to defective development of the–
A) Lens placode
B) Optic cup
C) Neural crest
D) Mesoderm
Answer: A) Lens placode
Explanation: The lens placode, derived from surface ectoderm, forms the lens. Defects produce congenital cataracts. Optic cup abnormalities affect retina, neural crest affects corneal stroma and sclera, and mesoderm contributes vascular tissues. Thus, A is correct. Cataract formation underscores the critical inductive interactions between optic vesicle and surface ectoderm in lens morphogenesis.
Chapter: Embryology; Topic: Neural Crest Cell Derivatives; Subtopic: Structures Arising From Neural Crest
Keyword Definitions:
Neural Crest Cells: Migratory embryonic cells giving rise to diverse tissues including ganglia and pigment cells.
Adrenal Medulla: Inner part of adrenal gland derived from neural crest chromaffin cells.
Pigment Cells (Melanocytes): Neural crest–derived cells producing melanin.
Corneal Stroma: Mesenchymal tissue derived largely from neural crest migration.
Retinal Pigmented Epithelium (RPE): Derived from neuroectoderm of optic cup, not neural crest.
1) Lead Question – 2016
All are derived from neural crest except?
A) Adrenal medulla
B) Pigment cell in skin
C) Corneal stroma
D) Retinal pigmented epithelium
Answer: D) Retinal pigmented epithelium
Explanation: Neural crest cells give rise to multiple structures including adrenal medulla, melanocytes, corneal stroma, craniofacial cartilage, and Schwann cells. The retinal pigmented epithelium (RPE), however, develops from the outer layer of the optic cup, which is derived from neuroectoderm, not neural crest. Thus, D is correct. Understanding this distinction helps differentiate between neuroectodermal and neural crest derivatives, particularly in congenital malformations affecting the eye, adrenal glands, or craniofacial structures. Neural crest migration is key to forming peripheral nervous system components and pigmentation patterns.
2) Which of the following is derived from neural crest cells?
A) Dorsal root ganglia
B) Anterior pituitary
C) Optic nerve
D) Lens
Answer: A) Dorsal root ganglia
Explanation: Neural crest cells form the dorsal root ganglia, autonomic ganglia, melanocytes, and Schwann cells. The anterior pituitary originates from oral ectoderm (Rathke’s pouch), the lens from surface ectoderm, and the optic nerve from neuroectoderm. Thus, A is correct. This distinction is clinically significant because neural crest defects can affect sensory and autonomic ganglia, presenting with neurological and pigmentation abnormalities in congenital syndromes such as Hirschsprung disease and Waardenburg syndrome.
3) A newborn presents with congenital absence of enteric ganglia in the colon. The embryological defect involves–
A) Neural crest migration
B) Neural tube closure
C) Endoderm differentiation
D) Mesoderm segmentation
Answer: A) Neural crest migration
Explanation: Hirschsprung disease results from failed migration of neural crest cells into the distal colon, leading to absence of enteric ganglia. Neural tube closure defects cause neural tube anomalies such as spina bifida. Endoderm forms gut epithelium and mesoderm forms muscle and connective tissue. Thus, A is correct. Neural crest migration defects lead to aganglionosis, impaired peristalsis, and colonic dilation, essential concepts for diagnosing congenital gastrointestinal motility disorders.
4) Melanocytes are derived from–
A) Surface ectoderm
B) Mesoderm
C) Neural crest cells
D) Endoderm
Answer: C) Neural crest cells
Explanation: Melanocytes originate from neural crest cells that migrate into the epidermis. Surface ectoderm forms epidermal keratinocytes, endoderm forms internal organ epithelium, and mesoderm forms connective tissues and muscles. Therefore, C is correct. Defects in melanocyte migration or function lead to disorders such as albinism and piebaldism, demonstrating their critical role in pigmentation and dermatologic development.
5) A child with suspected neurofibromatosis has multiple nerve sheath tumors. These tumors arise from cells derived from–
A) Astrocytes
B) Neural crest
C) Endoderm
D) Somitomeres
Answer: B) Neural crest
Explanation: Schwann cells, which form the basis of neurofibromas, are neural crest derivatives. Astrocytes derive from neuroectoderm, endoderm forms internal lining tissues, and somitomeres form skeletal muscle. Thus, B is correct. Neurofibromatosis features neural crest-derived tumors involving Schwann cells, emphasizing the diverse lineage and clinical importance of neural crest derivatives in peripheral nerve pathology.
6) Which of the following structures is not neural crest derived?
A) Schwann cells
B) Chromaffin cells
C) Parafollicular cells of thyroid
D) Retina
Answer: D) Retina
Explanation: The retina arises from neuroectoderm of the optic cup. Schwann cells, chromaffin cells of adrenal medulla, and parafollicular cells (C cells) of the thyroid are neural crest derivatives. Therefore, D is correct. Retinal development is tightly linked to optic vesicle formation, distinctly separate from migratory neural crest pathways that contribute to endocrine and peripheral nervous system structures.
7) A neonate presents with hypocalcemia and thymic aplasia. The embryological defect most likely involves–
A) Third pharyngeal pouch
B) Fourth pharyngeal pouch
C) Neural crest cells
D) Surface ectoderm
Answer: A) Third pharyngeal pouch
Explanation: DiGeorge syndrome involves maldevelopment of the third and fourth pharyngeal pouches, with the third giving rise to thymus and inferior parathyroids. Neural crest defects also contribute but the primary pouch abnormality is key. Surface ectoderm does not form these structures. Thus, A is correct. The syndrome results in T-cell deficiency and hypocalcemia due to thymic and parathyroid defects respectively.
8) Parafollicular (C) cells of the thyroid originate from–
A) Endoderm
B) Mesoderm
C) Neural crest
D) Surface ectoderm
Answer: C) Neural crest
Explanation: C cells derive from neural crest cells associated with the ultimobranchial body, which fuses with the thyroid. Endoderm forms thyroid follicles, mesoderm does not contribute, and surface ectoderm forms skin derivatives. Thus, C is correct. These cells secrete calcitonin and are involved in medullary thyroid carcinoma, emphasizing their clinical and embryological relevance.
9) Which of the following is derived from neuroectoderm rather than neural crest?
A) Retina
B) Odontoblasts
C) Melanocytes
D) Meninges (arachnoid/pia)
Answer: A) Retina
Explanation: The retina develops from the optic cup, a neuroectodermal derivative. Odontoblasts, melanocytes, and the pia-arachnoid mater arise from neural crest. Thus, A is correct. This distinction is crucial in ophthalmic embryology, explaining why retinal diseases reflect neural tissue behavior rather than neural crest–derived supportive structures.
10) A child presents with congenital absence of sympathetic ganglia. This defect involves failure of development of–
A) Neural tube
B) Neural crest cells
C) Somatic mesoderm
D) Intermediate mesoderm
Answer: B) Neural crest cells
Explanation: Sympathetic ganglia arise from migrating neural crest cells forming the autonomic nervous system. Neural tube forms CNS structures, somatic mesoderm produces body wall muscles, and intermediate mesoderm forms urogenital organs. Thus, B is correct. Such defects manifest clinically as autonomic dysfunction, emphasizing the importance of neural crest migration in forming the sympathetic chain.
11) Corneal endothelium and stroma arise mainly from–
A) Surface ectoderm
B) Mesoderm
C) Neural crest cells
D) Endoderm
Answer: C) Neural crest cells
Explanation: Neural crest cells migrate into the developing eye contributing to corneal stroma and endothelium. Surface ectoderm forms the lens and corneal epithelium, mesoderm contributes minimally to ocular structures, and endoderm plays no role. Thus, C is correct. Disorders of neural crest migration can result in anterior segment dysgenesis such as Axenfeld–Rieger anomaly.
Chapter: Embryology; Topic: Fetal Circulation & Umbilical Structures; Subtopic: Derivatives of Umbilical Arteries
Keyword Definitions:
Umbilical Arteries: Fetal vessels carrying deoxygenated blood to the placenta.
Distal Umbilical Artery: Portion that degenerates after birth forming a fibrous ligament.
Medial Umbilical Ligament: Fibrous remnant of the distal parts of umbilical arteries.
Superior Vesical Artery: Patent proximal part of umbilical arteries supplying the bladder.
Ligamentum Teres: Remnant of the left umbilical vein, not the artery.
1) Lead Question – 2016
Which of the following is remnant of distal umbilical artery?
A) Ligamentum Teres
B) Superior Vesical artery
C) Medial umbilical Ligament
D) Ligamentum arteriosum
Answer: C) Medial umbilical ligament
Explanation: After birth, the distal part of the umbilical artery fibroses and becomes the medial umbilical ligament. The proximal part remains patent as the superior vesical artery supplying the bladder. Ligamentum teres is derived from the left umbilical vein, while the ligamentum arteriosum is a remnant of the ductus arteriosus. Thus, the correct answer is C. The medial umbilical ligament runs on the internal surface of the anterior abdominal wall and is clinically significant because it forms an important landmark during pelvic surgery and laparoscopic procedures.
2) The proximal part of the umbilical artery in adults forms the–
A) Inferior epigastric artery
B) Superior vesical artery
C) Obturator artery
D) Deep circumflex artery
Answer: B) Superior vesical artery
Explanation: The proximal portion of the umbilical artery remains functional after birth and forms the superior vesical artery, which supplies the upper part of the urinary bladder. Other listed arteries have different embryological origins and are not derived from umbilical vessels. Thus, B is correct. This persistence reflects the fetal requirement for bladder blood supply continuing after birth, while the distal segment, no longer required for placental circulation, becomes fibrotic, forming the medial umbilical ligament.
3) A newborn undergoes surgery for bladder exstrophy. During the procedure, surgeons identify fibrous bands extending from the bladder to the abdominal wall. These are most likely–
A) Lateral umbilical folds
B) Medial umbilical ligaments
C) Round ligament of liver
D) Falx inguinalis
Answer: B) Medial umbilical ligaments
Explanation: Medial umbilical ligaments are remnants of the distal umbilical arteries and lie on the internal surface of the anterior abdominal wall. In bladder exstrophy, these structures are often visible surgically. Lateral umbilical folds contain inferior epigastric vessels. The round ligament of the liver is a remnant of the umbilical vein. Falx inguinalis is part of the conjoint tendon. Thus, B is correct because these ligaments represent the embryologic remains directly associated with bladder development and anterior abdominal wall anatomy.
4) Which of the following is derived from the left umbilical vein?
A) Medial umbilical ligament
B) Ligamentum venosum
C) Ligamentum teres hepatis
D) Ligamentum arteriosum
Answer: C) Ligamentum teres hepatis
Explanation: The left umbilical vein becomes the ligamentum teres hepatis after birth as placental circulation ceases. The medial umbilical ligament is derived from the distal umbilical artery, and the ligamentum arteriosum from the ductus arteriosus. The ligamentum venosum originates from the ductus venosus. Thus, C is correct. This structure runs along the free margin of the falciform ligament and is important surgically as a landmark separating the anatomical lobes of the liver.
5) A 3-day-old neonate shows absent closure of the distal umbilical arteries. This condition may present with–
A) Persistent abdominal wall pulsations
B) Umbilical granuloma
C) Patent urachus
D) Failure of ductus venosus closure
Answer: A) Persistent abdominal wall pulsations
Explanation: Failure of the distal umbilical arteries to fibrose may lead to persistent pulsatile vessels near the umbilicus. Umbilical granuloma results from incomplete epithelialization. Patent urachus connects bladder and umbilicus and involves urachal remnants, not arteries. Closure of the ductus venosus is unrelated. Thus, A is correct, reflecting the persistence of vascular flow in fetal arteries that normally become medial umbilical ligaments.
6) The ductus arteriosus becomes which adult structure?
A) Ligamentum venosum
B) Ligamentum teres
C) Ligamentum arteriosum
D) Medial umbilical ligament
Answer: C) Ligamentum arteriosum
Explanation: The ductus arteriosus, which shunts blood from the pulmonary trunk to the aorta during fetal life, closes after birth to form the ligamentum arteriosum. Ligamentum venosum derives from ductus venosus, ligamentum teres from the umbilical vein, and the medial umbilical ligament from distal umbilical arteries. Thus, C is correct. This structure is clinically significant because the left recurrent laryngeal nerve loops beneath it, making it important in thoracic surgical anatomy.
7) A newborn has a patent ductus arteriosus. This fetal vessel normally connects the–
A) Aorta to inferior vena cava
B) Pulmonary artery to aorta
C) Pulmonary vein to left atrium
D) SVC to right atrium
Answer: B) Pulmonary artery to aorta
Explanation: The ductus arteriosus diverts blood from the pulmonary trunk directly to the aorta, bypassing the non-functioning fetal lungs. After birth, increased oxygen tension induces closure. A patent ductus leads to a left-to-right shunt and continuous murmur. Other options do not represent fetal shunts. Thus, B is correct. Understanding fetal circulation helps clinicians diagnose congenital heart anomalies and manage neonatal cardiovascular conditions effectively.
8) The urachus in adults becomes the–
A) Medial umbilical ligament
B) Round ligament
C) Median umbilical ligament
D) Lateral umbilical fold
Answer: C) Median umbilical ligament
Explanation: The median umbilical ligament is the fibrotic remnant of the urachus, a fetal connection between the bladder and umbilicus. Medial umbilical ligaments arise from distal umbilical arteries, lateral umbilical folds contain inferior epigastric vessels, and the round ligament represents the umbilical vein. Thus, C is correct. A persistent urachus may produce urine discharge from the umbilicus, requiring surgical correction.
9) Which fetal structure allows oxygenated blood from the placenta to bypass the liver?
A) Ductus arteriosus
B) Ductus venosus
C) Foramen ovale
D) Umbilical artery
Answer: B) Ductus venosus
Explanation: The ductus venosus channels oxygen-rich blood from the umbilical vein directly into the IVC, bypassing hepatic circulation. The ductus arteriosus bypasses the lungs, and the foramen ovale shunts blood between atria. The umbilical artery carries deoxygenated blood. Thus, B is correct. Closure of this structure after birth forms the ligamentum venosum, important in hepatic surgical anatomy.
10) A surgeon tracing the medial umbilical ligament notes its course toward the–
A) Umbilicus
B) Liver
C) Renal hilum
D) Lumbar vertebrae
Answer: A) Umbilicus
Explanation: The medial umbilical ligament courses superiorly on the posterior surface of the anterior abdominal wall toward the umbilicus. It marks the obliterated distal umbilical artery. It does not extend toward the liver (round ligament), renal hilum, or lumbar vertebrae. Thus, A is correct. These ligaments create identifiable folds important in laparoscopic hernia repair, serving as landmarks that help differentiate direct and indirect inguinal hernias.
11) A neonate with umbilical discharge containing urine likely has a defect involving the–
A) Medial umbilical ligament
B) Urachus
C) Umbilical vein
D) Ductus arteriosus
Answer: B) Urachus
Explanation: A patent urachus causes urine leakage from the umbilicus, resulting from failure of the allantoic duct to close. The medial umbilical ligament forms from umbilical artery remnants and is unrelated. The umbilical vein becomes the ligamentum teres, while the ductus arteriosus forms the ligamentum arteriosum. Thus, B is correct. Recognizing clinical signs helps differentiate urachal anomalies from other umbilical pathologies, ensuring proper surgical intervention.
Chapter: Embryology; Topic: Development of Head and Neck; Subtopic: Embryological Origin of Tongue Muscles
Keyword Definitions:
Occipital Myotomes: Paraxial mesodermal segments migrating to form intrinsic and extrinsic tongue muscles.
Pharyngeal Arches: Embryonic structures contributing to mucosa, cartilage, and skeletal elements of the tongue.
Lateral Plate Mesoderm: Mesoderm forming body wall musculature, not tongue muscles.
Intermediate Mesoderm: Mesoderm responsible for urogenital development.
Hypoglossal Nerve Migration: Nerve accompanying occipital myotomes during tongue muscle development.
1) Lead Question – 2016
Tongue muscles are derived from:
A) Lateral plate mesoderm
B) Occipital myotome
C) Intermediate mesoderm
D) Cervical myotome
Answer: B) Occipital myotome
Explanation: Tongue muscles originate from occipital myotomes, a set of paraxial mesodermal segments that migrate anteriorly along with the hypoglossal nerve. These myogenic precursors give rise to both intrinsic and extrinsic tongue musculature. Lateral plate mesoderm forms limb and body wall muscles, not tongue muscles. Intermediate mesoderm is responsible for kidney and gonadal development. Cervical myotomes do not contribute to tongue formation. Therefore, the correct answer is B, as occipital myotomes are solely responsible for the muscular component of the developing tongue, ensuring coordinated movement essential for swallowing and speech.
2) The epiglottis develops primarily from which pharyngeal arch?
A) First arch
B) Second arch
C) Third arch
D) Fourth arch
Answer: D) Fourth arch
Explanation: The epiglottis arises mainly from the hypobranchial eminence derived predominantly from the fourth pharyngeal arch. The first and second arches form anterior tongue structures, while the third contributes to posterior tongue mucosa. The fourth arch provides material for the epiglottis and laryngeal cartilages. Therefore, the correct answer is D. This structure’s embryological origin explains its innervation pattern and functional association with laryngeal development, particularly its role in protecting the airway during swallowing, contributing to coordinated respiratory and digestive functions.
3) A newborn has paralysis of most tongue muscles. The nerve likely injured is the–
A) Glossopharyngeal nerve
B) Vagus nerve
C) Hypoglossal nerve
D) Facial nerve
Answer: C) Hypoglossal nerve
Explanation: The hypoglossal nerve (CN XII) supplies all intrinsic and extrinsic tongue muscles except palatoglossus. Since these muscles originate from occipital myotomes that migrate with CN XII, damage to this nerve leads to tongue deviation, weak protrusion, and impaired swallowing. The glossopharyngeal nerve mainly provides sensation to the posterior tongue, not motor control. The vagus nerve supplies palatoglossus only. The facial nerve innervates taste buds of the anterior two-thirds but not musculature. Therefore, the correct answer is C, as hypoglossal nerve injury most directly affects tongue muscle function.
4) The mucosa of the anterior two-thirds of the tongue develops from–
A) First pharyngeal arch
B) Second pharyngeal arch
C) Third pharyngeal arch
D) Fourth pharyngeal arch
Answer: A) First pharyngeal arch
Explanation: The anterior two-thirds of the tongue originate from the first pharyngeal arch, specifically from the lateral lingual swellings and tuberculum impar. This region receives general sensation from the mandibular division of the trigeminal nerve. The second arch contributes transiently but regresses. The third arch forms the posterior one-third mucosa, while the fourth arch forms the epiglottic region. Thus, A is correct, reflecting the distinct embryologic segmentation of the tongue crucial for understanding its innervation patterns and clinical correlations involving sensory deficits.
5) A child with impaired swallowing is found to have incomplete tongue muscle development. The embryological defect is most likely in–
A) Occipital somites
B) Cardiac neural crest cells
C) Intermediate mesoderm
D) Sclerotome
Answer: A) Occipital somites
Explanation: Tongue musculature arises from occipital somites, which migrate anteriorly to form intrinsic and extrinsic muscles. A defect here leads to poor motor control affecting swallowing and speech. Cardiac neural crest cells contribute to heart and great vessel development. Intermediate mesoderm forms urogenital organs. Sclerotome produces vertebrae and ribs. Therefore, the correct answer is A. Disruption of occipital somite migration is critical because it directly affects muscular formation and coordination of the tongue, essential for feeding and early speech development.
6) Sensory innervation of the posterior third of the tongue is provided by–
A) Facial nerve
B) Glossopharyngeal nerve
C) Hypoglossal nerve
D) Trigeminal nerve
Answer: B) Glossopharyngeal nerve
Explanation: The posterior third of the tongue originates from the third pharyngeal arch and is supplied by the glossopharyngeal nerve (CN IX). This nerve carries both taste and general sensation from this region. The facial nerve innervates taste buds of the anterior two-thirds. The trigeminal nerve provides general sensation to the anterior tongue. The hypoglossal nerve is motor only. Thus, B is correct, reflecting the embryologic and neuroanatomic foundations of tongue innervation, vital in diagnosing sensory loss and taste abnormalities.
7) A 6-year-old boy presents with difficulty moving his tongue after neck surgery. Which structure was most likely damaged?
A) Lingual nerve
B) External laryngeal nerve
C) Hypoglossal nerve
D) Recurrent laryngeal nerve
Answer: C) Hypoglossal nerve
Explanation: The hypoglossal nerve (CN XII) innervates intrinsic and extrinsic tongue muscles. Damage causes impaired protrusion, deviation toward the injured side, and articulation difficulty. The lingual nerve provides sensation but not motor function. External and recurrent laryngeal nerves supply laryngeal muscles and do not control tongue movement. Therefore, C is correct. This nerve’s proximity to the carotid artery and its course across the neck make it susceptible during surgical procedures, emphasizing its clinical importance in preserving speech and swallowing function.
8) Taste sensation from the anterior two-thirds of the tongue is carried by–
A) Chorda tympani
B) Glossopharyngeal nerve
C) Vagus nerve
D) Hypoglossal nerve
Answer: A) Chorda tympani
Explanation: Taste fibers from the anterior two-thirds of the tongue travel via the chorda tympani branch of the facial nerve. This reflects the transient contribution of the second pharyngeal arch to tongue development. The glossopharyngeal nerve conveys taste from the posterior third. The vagus nerve carries taste from the epiglottis. The hypoglossal nerve supplies motor fibers only. Thus, A is correct. Understanding this distribution is key in evaluating taste disturbances and differentiating sensory deficits due to facial nerve lesions.
9) A newborn with midline tongue cyst likely has a developmental defect in–
A) Tuberculum impar
B) Pharyngeal pouch
C) Intermediate mesoderm
D) Occipital somite
Answer: A) Tuberculum impar
Explanation: The tuberculum impar contributes to the midline portion of the anterior tongue. Abnormal fusion or persistence may lead to midline cysts or lesions. Pharyngeal pouches form glands and do not form tongue tissue. Intermediate mesoderm forms urogenital organs. Occipital somites form tongue muscles, not mucosa. Therefore, A is correct because abnormalities in this early mesenchymal structure cause midline developmental anomalies clinically observed as cysts or masses requiring evaluation.
10) A patient experiences difficulty elevating the tongue. The affected muscle is most likely–
A) Genioglossus
B) Hyoglossus
C) Styloglossus
D) Palatoglossus
Answer: D) Palatoglossus
Explanation: Palatoglossus elevates the posterior tongue and is unique as it is innervated by the vagus nerve via the pharyngeal plexus. Other tongue muscles derive from occipital myotomes and are supplied by the hypoglossal nerve. Genioglossus protrudes, hyoglossus depresses, and styloglossus retracts the tongue. Therefore, D is correct. Understanding these muscles’ embryologic origins and innervations is vital for diagnosing tongue movement disorders and determining whether pathology is muscular or neural in origin.
11) Failure of migration of occipital myotomes during development would primarily affect–
A) Tongue musculature
B) Pharyngeal arch skeleton
C) Parathyroid glands
D) Thyroid cartilage
Answer: A) Tongue musculature
Explanation: Occipital myotomes migrate anteriorly with the hypoglossal nerve to form intrinsic and extrinsic tongue muscles. A failure in this migration impairs muscle formation, resulting in defective movement, poor feeding, and impaired speech development. Pharyngeal arch skeleton and thyroid cartilage arise from neural crest cells. Parathyroid glands originate from third and fourth pharyngeal pouches. Therefore, A is correct because the muscular component of the tongue depends solely on successful occipital myotome migration during embryogenesis.
Chapter: Embryology; Topic: Development of Gastrointestinal Tract; Subtopic: Foregut Derivatives
Keyword Definitions:
• Foregut: Portion of primitive gut tube forming pharynx, esophagus, stomach, upper duodenum, liver, pancreas.
• Midgut: Part of primitive gut forming distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal transverse colon.
• Hindgut: Part of primitive gut forming distal transverse colon, descending colon, sigmoid colon, rectum, anal canal above pectinate line.
• Pancreas: Foregut derivative formed by dorsal and ventral buds.
• Liver: Foregut derivative forming hepatic diverticulum.
• Cecum: Dilatation of midgut loop forming cecum and appendix.
Lead Question - 2015
Which of the following is not a derivative of foregut?
a) Cecum
b) Duodenum
c) Liver
d) Pancreas
Explanation (Answer: a) Cecum)
The cecum is a midgut derivative, not a foregut derivative. The foregut gives rise to esophagus, stomach, liver, pancreas, and upper half of duodenum. The cecum originates from the midgut loop and forms the base for the appendix. The liver and pancreas arise from foregut endoderm and play chief roles in digestive enzyme regulation and metabolism.
1. Which of the following structures develops from midgut?
a) Stomach
b) Cecum
c) Gallbladder
d) Pancreatic duct
Explanation (Answer: b) Cecum)
The cecum is derived from the midgut as part of the midgut loop. It develops as an outpouching at the junction of ileum and colon. The stomach, gallbladder, and pancreatic ducts arise from foregut endoderm. Midgut structures include ileum, appendix, ascending colon, and proximal transverse colon. Rotation abnormalities affect cecum position clinically.
2. Which organ originates from hepatic diverticulum?
a) Spleen
b) Liver
c) Kidney
d) Appendix
Explanation (Answer: b) Liver)
The liver develops from the hepatic diverticulum, a foregut endodermal outgrowth. It invades septum transversum forming hepatocytes, bile ducts, and intrahepatic structures. The spleen arises from mesoderm of dorsal mesogastrium, not gut tube. Kidney develops from intermediate mesoderm while appendix originates from midgut-derived cecum.
3. The pancreas develops from:
a) Hindgut
b) Mesoderm
c) Foregut
d) Ectoderm
Explanation (Answer: c) Foregut)
The pancreas forms from dorsal and ventral pancreatic buds arising from the foregut endoderm. These buds fuse to form head, body, and tail. Pancreatic duct anomalies occur due to improper fusion producing pancreas divisum. Insulin-producing beta cells originate from endodermal lineage, not mesoderm or ectoderm, confirming foregut derivation.
4. Lower half of duodenum develops from:
a) Foregut
b) Midgut
c) Hindgut
d) Allantois
Explanation (Answer: b) Midgut)
The lower half of duodenum and proximal jejunum come from midgut. The upper half is from foregut, receiving bile and pancreatic ducts. Knowing the origin helps understand blood supply division—foregut supplied by celiac artery and midgut by superior mesenteric artery, explaining mixed vascular patterns in duodenum.
5. Which artery supplies foregut derivatives?
a) Inferior mesenteric artery
b) Superior mesenteric artery
c) Celiac artery
d) Renal artery
Explanation (Answer: c) Celiac artery)
Foregut organs, including stomach, liver, pancreas, spleen (via splenic branch), are supplied by the celiac artery. This arterial trunk branches into left gastric, splenic, and common hepatic arteries. Superior mesenteric supplies midgut while inferior mesenteric supplies hindgut. Knowledge of embryology guides vascular surgical approaches.
6. A newborn with annular pancreas has obstruction due to abnormal rotation of:
a) Dorsal pancreatic bud
b) Ventral pancreatic bud
c) Hepatic diverticulum
d) Midgut loop
Explanation (Answer: b) Ventral pancreatic bud)
Annular pancreas occurs due to abnormal migration of the ventral pancreatic bud encircling duodenum, causing obstruction. The bud encases the second part of duodenum. Symptoms include vomiting and gastric distension in neonates. It is a foregut developmental anomaly involving pancreatic rotation failure.
7. Failure of recanalization of duodenum leads to:
a) Duodenal atresia
b) Hirschsprung disease
c) Omphalocele
d) Pyloric stenosis
Explanation (Answer: a) Duodenal atresia)
Duodenal atresia results from failure of recanalization of duodenal lumen during development. Presents with bilious vomiting and “double bubble” sign on X-ray. It involves both foregut- and midgut-derived portions. Associated with Down syndrome. Treatment requires surgical correction to restore intestinal continuity.
8. Cecum is supplied by which artery?
a) Celiac trunk
b) Middle colic artery
c) Ileocolic artery
d) Inferior mesenteric artery
Explanation (Answer: c) Ileocolic artery)
The cecum, as a midgut derivative, is supplied by the ileocolic artery, a branch of superior mesenteric artery. Blood supply pattern reflects embryonic origin. Midgut ischemia or volvulus may compromise this region. The celiac trunk supplies foregut organs and not cecum, confirming its separate developmental lineage.
9. Which of the following is derived from midgut but supplied by celiac trunk?
a) Appendix
b) Duodenum (lower half)
c) Jejunum
d) None
Explanation (Answer: d) None)
Foregut derivatives are supplied by celiac trunk while midgut derivatives by superior mesenteric artery. No midgut structure receives major supply from celiac trunk. Duodenum transitions at papilla; proximal is foregut-supplied, distal is midgut-supplied. Appendix, jejunum, and transverse colon derive from midgut and are SMA-dependent.
10. A neonate with bilious vomiting and polyhydramnios likely has obstruction at:
a) Pylorus
b) Duodenum
c) Rectum
d) Cecum
Explanation (Answer: b) Duodenum)
Duodenal obstruction due to atresia or annular pancreas (both involving foregut structures) causes bilious vomiting and polyhydramnios. The “double bubble” sign on radiograph indicates dilation of stomach and proximal duodenum. Cecum obstruction typically causes distal bowel symptoms, not bilious vomiting. Early surgical repair is essential.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Formation of Trigone and Derivatives of Mesonephric Duct
Keyword Definitions:
• Trigone of bladder: Smooth triangular area inside urinary bladder derived from incorporated mesonephric ducts.
• Mesonephric duct (Wolffian duct): Embryonic structure forming male genital ducts and contributing to trigone formation.
• Müllerian duct: Embryonic paramesonephric duct forming female reproductive tract; regresses in males.
• Urothelium: Transitional epithelium lining urinary bladder from endoderm.
• Cloaca: Primitive chamber dividing into urogenital sinus and anorectal canal.
• Urogenital sinus: Endodermal structure forming bladder except trigone region.
Lead Question - 2015
Trigone of bladder is derived from?
a) Mesonephric duct
b) Paramesonephric duct
c) Absorbed anal membrane
d) Müllerian duct
Explanation (Answer: a) Mesonephric duct)
The trigone of the urinary bladder develops from the mesonephric (Wolffian) ducts, which are absorbed into the posterior wall of the developing bladder. Although the trigone initially has mesodermal origin, its epithelium later becomes overgrown by endodermal urothelium, giving it the same epithelial lining as the rest of the bladder. It forms a smooth triangular area between ureteric openings and the internal urethral orifice.
1. Urothelium of the urinary bladder develops from:
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neural crest
Explanation (Answer: a) Endoderm)
The urothelium lining the bladder and urethra develops from the endoderm of the urogenital sinus. Although the trigone initially forms from mesodermal mesonephric ducts, it is secondarily covered by endodermal epithelium. Thus, the entire bladder ultimately has an endodermal epithelial lining, ensuring uniform urothelial characteristics.
2. Ureteric bud gives rise to all except:
a) Renal pelvis
b) Ureter
c) Collecting ducts
d) Detrusor muscle
Explanation (Answer: d) Detrusor muscle)
The ureteric bud forms the ureter, renal pelvis, calyces, and collecting ducts. The detrusor muscle arises from the splanchnic mesoderm surrounding the urogenital sinus, not the ureteric bud. The bud interacts with metanephric mesenchyme to initiate kidney development but does not contribute to bladder musculature formation.
3. Which embryonic structure forms the lower part of the vagina?
a) Müllerian duct
b) Urogenital sinus
c) Mesonephric duct
d) Cloacal membrane
Explanation (Answer: b) Urogenital sinus)
The lower vagina develops from the urogenital sinus through formation of the sinovaginal bulbs. The Müllerian ducts contribute to the upper vagina, uterus, and fallopian tubes. The distinction between upper Müllerian origin and lower sinus origin explains clinical presentations such as vaginal atresia or septal anomalies.
4. Which structure develops from mesonephric duct in males?
a) Uterus
b) Epididymis
c) Labia majora
d) Vagina
Explanation (Answer: b) Epididymis)
The mesonephric duct, under the influence of testosterone, forms the epididymis, vas deferens, seminal vesicle, and ejaculatory ducts in males. In females, this duct largely regresses, leaving remnants such as Gartner’s duct. It also contributes to trigone development but not to female reproductive structures.
5. A newborn presents with smooth bladder floor and abnormal ureteric openings. Developmental defect lies in:
a) Metanephric blastema
b) Mesonephric duct absorption
c) Urogenital sinus fusion
d) Cloacal membrane rupture
Explanation (Answer: b) Mesonephric duct absorption)
The trigone of the bladder forms when the mesonephric ducts are absorbed into the posterior bladder wall. Failure results in abnormal ureteric openings, vesicoureteral reflux, or duplicated ureters. The smooth trigone area becomes distorted, affecting proper urinary flow patterns and increasing infection risk.
6. The ureteric bud develops from which structure?
a) Müllerian duct
b) Mesonephric duct
c) Allantois
d) Pronephric duct
Explanation (Answer: b) Mesonephric duct)
The ureteric bud arises from the mesonephric duct near its attachment to the cloaca. It invades the metanephric mesenchyme and induces kidney formation. The ureteric bud forms collecting ducts, renal pelvis, calyces, and ureters. Defects in bud development lead to renal agenesis, duplex systems, or pelvic kidney formation.
7. The bladder (except trigone) originates from:
a) Mesonephric duct
b) Urogenital sinus
c) Allantois
d) Mesenchyme of cloaca
Explanation (Answer: b) Urogenital sinus)
The bladder, excluding the trigone, originates from the endodermal urogenital sinus. Although mesonephric ducts contribute mesoderm to the trigone region initially, the endodermal lining of the bladder eventually overgrows this region. The body, apex, and neck of the bladder are all sinus-derived, ensuring uniform epithelium.
8. Which of the following is a remnant of the allantois?
a) Ovarian ligament
b) Urachus
c) Gartner’s duct
d) Appendix epididymis
Explanation (Answer: b) Urachus)
The allantois, a vestigial embryonic structure, becomes the urachus, connecting bladder apex to umbilicus. Postnatally, it becomes the median umbilical ligament. Failure of closure leads to urachal cysts, fistulae, or sinuses, causing urinary discharge from the umbilicus or infection in infants.
9. Vesicoureteral reflux is due to abnormal development of:
a) Müllerian duct
b) Ureterovesical junction
c) Allantois
d) Cloacal membrane
Explanation (Answer: b) Ureterovesical junction)
Vesicoureteral reflux arises due to improper formation of the ureterovesical junction. Defective insertion of ureters into the bladder wall (derived from mesonephric duct incorporation) results in retrograde urine flow. This leads to recurrent infections, hydronephrosis, and renal scarring in pediatric patients.
10. A child has duplicated ureter. This results from abnormal division of:
a) Mesonephric duct
b) Pronephric tubule
c) Ureteric bud
d) Urogenital sinus
Explanation (Answer: c) Ureteric bud)
Duplicated ureters occur when the ureteric bud prematurely divides into two buds, each inducing its own collecting system. This may cause ureteral ectopia or reflux. The primary origin of the bud is the mesonephric duct, but duplication occurs after budding, not from mesonephric branching itself.
Chapter: Embryology; Topic: Development of Nervous System; Subtopic: Origin of Glial Cells
Keyword Definitions:
• Microglial cells: Phagocytic glial cells of the CNS derived from mesodermal mesenchyme.
• Macroglial cells: Glial cells including astrocytes and oligodendrocytes derived from neuroectoderm.
• Oligodendrocytes: Myelin-forming glial cells in CNS derived from neuroectoderm.
• Ependymal cells: Neuroectodermal cells lining ventricles and central canal of spinal cord.
• Mesoderm: Middle germ layer giving rise to microglia, blood cells, and connective tissues.
• Neuroectoderm: Embryonic tissue forming neurons, macroglia, retina, and CNS structures.
Lead Question - 2015
Which of glial cell is mesodermal in origin -
a) Macroglial cells
b) Microglial cells
c) Oligodendrocytes
d) Ependymal cells
Explanation (Answer: b) Microglial cells)
Microglial cells are the only glial cells derived from the mesoderm. They originate from mesenchymal cells of embryonic yolk sac and migrate into the CNS. They act as resident macrophages and participate in immune surveillance, phagocytosis, debris removal, and inflammatory response. All other glial cells—astrocytes, oligodendrocytes, and ependymal cells—are derived from neuroectoderm.
1. Astrocytes are derived from:
a) Mesoderm
b) Neuroectoderm
c) Endoderm
d) Neural crest
Explanation (Answer: b) Neuroectoderm)
Astrocytes develop from the neuroectoderm and perform essential supportive functions such as maintaining blood–brain barrier, neurotransmitter uptake, and ionic balance. They are macroglial cells, unlike microglia, which originate from mesoderm. Astrocytic dysfunction may contribute to neurological conditions like gliosis, epilepsy, and neuroinflammation.
2. Which glial cell is responsible for myelinating CNS axons?
a) Schwann cells
b) Oligodendrocytes
c) Microglial cells
d) Astrocytes
Explanation (Answer: b) Oligodendrocytes)
Oligodendrocytes originate from the neuroectoderm and myelinate multiple CNS axons. Each oligodendrocyte may supply myelin to several neurons. Schwann cells perform similar functions in the PNS but are derived from neural crest. Microglia, although glial in name, are immune cells from mesodermal origin and do not participate in myelination.
3. Which glial cell proliferates most actively after CNS injury?
a) Ependymal cells
b) Microglial cells
c) Oligodendrocytes
d) Astrocytes
Explanation (Answer: b) Microglial cells)
Microglial cells, derived from mesoderm, proliferate rapidly after CNS injury and act as phagocytes removing damaged tissue. They secrete cytokines, initiate inflammatory responses, and contribute to neurodegeneration in severe injuries. Their activation is an indicator of CNS pathology, seen in stroke, infections, trauma, and neurodegenerative diseases.
4. Ependymal cells line which structure?
a) Blood–brain barrier
b) Ventricles of the brain
c) Optic nerve
d) Peripheral nerves
Explanation (Answer: b) Ventricles of the brain)
Ependymal cells are derived from neuroectoderm and line the brain ventricles and central canal of the spinal cord. They form the epithelial component of the choroid plexus and help circulate cerebrospinal fluid. They are not mesodermal like microglia and do not form myelin or participate in immune surveillance.
5. A patient with brain infection shows increased activation of phagocytic glial cells. Which cells are these?
a) Astrocytes
b) Microglial cells
c) Oligodendrocytes
d) Ependymal cells
Explanation (Answer: b) Microglial cells)
Microglial cells, the CNS macrophages, are mesodermal in origin and increase during infection or inflammation. They remove pathogens and debris, present antigens, and release inflammatory mediators. Astrocytes and oligodendrocytes do not exhibit phagocytic properties. Ependymal cells maintain ventricular lining but do not participate in immune responses.
6. Schwann cells are derived from which embryonic structure?
a) Neuroectoderm
b) Surface ectoderm
c) Neural crest
d) Mesoderm
Explanation (Answer: c) Neural crest)
Schwann cells, responsible for myelinating peripheral nerves, originate from neural crest cells. Unlike CNS oligodendrocytes, Schwann cells myelinate only one axon segment each. Neural crest derivatives include melanocytes, adrenal medulla, and craniofacial structures. They are not mesodermal like microglia.
7. Which glial cell participates in forming the blood–brain barrier (BBB)?
a) Oligodendrocytes
b) Astrocytes
c) Microglial cells
d) Ependymal cells
Explanation (Answer: b) Astrocytes)
Astrocytes extend foot processes that envelope capillaries and help maintain the blood–brain barrier. They regulate extracellular ion concentration, uptake neurotransmitters, and support neuronal metabolism. They are neuroectodermal and structurally distinct from mesoderm-derived microglia that function as CNS macrophages.
8. A brain biopsy reveals proliferative cells of mesodermal origin. These are most likely:
a) Astrocytes
b) Microglial cells
c) Ependymal cells
d) Oligodendrocytes
Explanation (Answer: b) Microglial cells)
Microglial cells proliferate in response to CNS injury or infection. They are mesodermal in origin and are related to monocyte–macrophage lineage. Their presence indicates inflammation or tissue degeneration. Other glial cells like astrocytes and ependymal cells are derived from neuroectoderm and do not show similar macrophage-like activity.
9. Which glial cell is involved in myelinating peripheral axons?
a) Astrocytes
b) Oligodendrocytes
c) Microglial cells
d) Schwann cells
Explanation (Answer: d) Schwann cells)
Schwann cells, derived from neural crest, are involved in myelinating PNS axons. Each cell covers a single axon segment. In contrast, oligodendrocytes myelinate CNS axons. Microglia, the mesodermal phagocytes, do not participate in myelination. Damage to Schwann cells results in demyelinating neuropathies such as Guillain–Barré syndrome.
10. A newborn presents with enlarged ventricles due to impaired CSF flow. Which glial cell malfunction is likely responsible?
a) Microglial cells
b) Ependymal cells
c) Astrocytes
d) Oligodendrocytes
Explanation (Answer: b) Ependymal cells)
Ependymal cells line ventricles and participate in CSF flow regulation through ciliary action. Their dysfunction leads to obstructed CSF movement, resulting in hydrocephalus. Microglia, although mesodermal, are not involved in CSF circulation. Astrocytes and oligodendrocytes have other supportive roles but do not regulate ventricular fluid flow.
Chapter: Embryology; Topic: Development of Endocrine System; Subtopic: Development of Pituitary Gland (Rathke’s Pouch Derivatives)
Keyword Definitions:
• Rathke’s pouch: Ectodermal upward growth from stomodeum that forms anterior pituitary components.
• Adenohypophysis: Anterior pituitary part derived from Rathke’s pouch producing trophic hormones.
• Pars distalis: Largest part of anterior pituitary developed from Rathke’s pouch.
• Pars tuberalis: Pituitary segment derived from Rathke’s pouch surrounding infundibular stalk.
• Neurohypophysis: Posterior pituitary derived from infundibulum of diencephalon.
• Pineal gland: Neuroectodermal gland producing melatonin located in epithalamus.
Lead Question - 2015
Which of the following is a derivative of Rathke's pouch?
a) Pars tuberalis
b) Neurohypophysis
c) Posterior pituitary
d) Pineal gland
Explanation (Answer: a) Pars tuberalis)
Rathke’s pouch, a stomodeal ectodermal diverticulum, gives rise to the pars distalis, pars intermedia, and pars tuberalis of the anterior pituitary. The posterior pituitary (neurohypophysis) derives from neuroectoderm of the infundibulum, while the pineal gland originates from the roof of the diencephalon. The pars tuberalis surrounds the infundibular stalk and plays regulatory roles in endocrine function.
1. Which part of the pituitary develops from the infundibulum?
a) Pars distalis
b) Pars intermedia
c) Neurohypophysis
d) Pars tuberalis
Explanation (Answer: c) Neurohypophysis)
The neurohypophysis (posterior pituitary) develops from a downward extension of the diencephalon known as the infundibulum. It consists of axonal terminals of hypothalamic neurons storing ADH and oxytocin. In contrast, Rathke’s pouch gives rise to pars distalis, pars intermedia, and pars tuberalis of the anterior pituitary, all of ectodermal origin.
2. Pars distalis primarily secretes which hormone?
a) ADH
b) Oxytocin
c) Growth hormone
d) Melatonin
Explanation (Answer: c) Growth hormone)
The pars distalis, derived from Rathke’s pouch, is the largest functional portion of the anterior pituitary. It secretes several hormones including GH, ACTH, TSH, FSH, LH, and prolactin. GH stimulates growth and protein synthesis. ADH and oxytocin originate from hypothalamus and are stored in the posterior pituitary, while melatonin is secreted by the pineal gland.
3. Craniopharyngioma originates from remnants of:
a) Infundibulum
b) Rathke’s pouch
c) Pineal gland
d) Neurohypophysis
Explanation (Answer: b) Rathke’s pouch)
Craniopharyngioma is a benign but invasive tumor originating from epithelial remnants of Rathke’s pouch. It commonly presents in children with headaches, visual impairment, and growth disturbances due to compression of the optic chiasma and pituitary gland. Calcifications are characteristic on imaging. It is embryologically linked to anterior pituitary development.
4. Which pituitary lobe stores oxytocin and ADH?
a) Pars distalis
b) Pars intermedia
c) Pars tuberalis
d) Posterior pituitary
Explanation (Answer: d) Posterior pituitary)
The posterior pituitary stores and releases ADH and oxytocin, although these hormones are synthesized in the hypothalamus. It derives from neuroectoderm of the infundibulum, unlike anterior pituitary components derived from Rathke’s pouch. Damage to the posterior pituitary causes diabetes insipidus due to lack of ADH regulation.
5. A 12-year-old presents with delayed growth and calcified suprasellar mass. Likely diagnosis?
a) Prolactinoma
b) Craniopharyngioma
c) Pinealoma
d) Pituitary apoplexy
Explanation (Answer: b) Craniopharyngioma)
A calcified suprasellar mass in a child suggests craniopharyngioma, a tumor derived from Rathke’s pouch remnants. Symptoms include visual field defects, growth failure due to pituitary compression, and hormonal imbalance. MRI shows cystic and solid components with calcification. Treatment involves surgical removal and hormone replacement therapy.
6. Pars intermedia is responsible for secretion of:
a) ACTH
b) MSH
c) TSH
d) Prolactin
Explanation (Answer: b) MSH)
The pars intermedia, originating from Rathke’s pouch, secretes melanocyte-stimulating hormone (MSH). This part is prominent in lower vertebrates but rudimentary in humans. It regulates melanogenesis. Other anterior pituitary hormones such as ACTH, TSH, and prolactin are secreted by pars distalis, not pars intermedia.
7. Posterior pituitary is derived from which embryonic layer?
a) Surface ectoderm
b) Neural ectoderm
c) Mesoderm
d) Endoderm
Explanation (Answer: b) Neural ectoderm)
The posterior pituitary (neurohypophysis) develops from the neural ectoderm of the diencephalon. It remains connected to hypothalamus through the infundibular stalk and releases stored oxytocin and ADH. This contrasts with anterior pituitary derivatives from surface ectoderm via Rathke’s pouch.
8. A lesion affecting pars tuberalis disrupts regulation of:
a) Thyroid function
b) Pineal secretion
c) Hypothalamic–pituitary signaling
d) ADH storage
Explanation (Answer: c) Hypothalamic–pituitary signaling)
The pars tuberalis surrounds the pituitary stalk and is involved in transport of hypothalamic releasing hormones to anterior pituitary. Damage to this region affects endocrine regulation, leading to hormonal imbalances. Since it derives from Rathke’s pouch, its dysfunction affects anterior rather than posterior pituitary function.
9. Which structure forms due to fusion between Rathke’s pouch and infundibulum?
a) Hypophyseal stalk
b) Complete pituitary gland
c) Optic cup
d) Pineal body
Explanation (Answer: b) Complete pituitary gland)
The pituitary gland forms by union of Rathke’s pouch (anterior pituitary origin) and infundibulum (posterior pituitary origin). This dual embryologic origin explains distinct hormonal functions. Failure of proper fusion may cause pituitary hypoplasia or ectopic pituitary tissue along the stalk pathway.
10. A tumor compressing only the posterior pituitary will most likely cause:
a) Hyperprolactinemia
b) Panhypopituitarism
c) Diabetes insipidus
d) Acromegaly
Explanation (Answer: c) Diabetes insipidus)
Compression of the posterior pituitary disrupts ADH release, resulting in central diabetes insipidus characterized by polyuria and polydipsia. Anterior pituitary functions, derived from Rathke’s pouch, remain intact, so no hyperprolactinemia or growth hormone excess occurs unless broader pituitary compression develops.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of Ocular Layers and Optic Cup Formation
Keyword Definitions:
• Optic vesicle: Outgrowth from the forebrain (diencephalon) that gives rise to the optic cup and optic stalk.
• Optic cup: Double-layered structure derived from neural ectoderm that forms the retina and iris epithelium.
• Neural ectoderm: Ectodermal tissue of neural origin giving rise to CNS structures, including retina and optic nerve.
• Surface ectoderm: External ectodermal layer forming lens, corneal epithelium, and eyelids.
• Mesoderm: Middle germ layer contributing to extraocular muscles and vascular components of the eye.
• Neural crest cells: Migratory cells contributing to choroid, sclera, and corneal endothelium.
Lead Question - 2015
Optic cup is derived from?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation (Answer: a) Neural ectoderm)
The optic cup develops as an invagination of the optic vesicle, which itself is derived from the neural ectoderm of the forebrain (diencephalon). It forms a double-walled cup whose inner layer develops into the neural retina and outer layer into the retinal pigment epithelium (RPE). Thus, neural ectoderm gives rise to the essential sensory components of the eye.
1. The lens of the eye develops from which embryonic layer?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Endoderm
Explanation (Answer: b) Surface ectoderm)
The lens develops from the surface ectoderm overlying the optic vesicle. The optic vesicle induces the ectoderm to form a lens placode, which invaginates to form the lens vesicle. This lens later differentiates into lens fibers. Neural ectoderm forms the retina, whereas mesoderm and neural crest form supportive structures like sclera and choroid.
2. The retinal pigment epithelium (RPE) of the eye develops from:
a) Surface ectoderm
b) Neural crest
c) Outer layer of optic cup
d) Mesoderm
Explanation (Answer: c) Outer layer of optic cup)
The outer layer of the optic cup, derived from neural ectoderm, forms the retinal pigment epithelium (RPE). The inner layer forms the neural retina. Together, these layers constitute the optic cup. The RPE plays a critical role in photoreceptor maintenance and absorption of scattered light, essential for visual clarity.
3. The corneal epithelium is derived from:
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest cells
Explanation (Answer: b) Surface ectoderm)
The corneal epithelium develops from the surface ectoderm, while the corneal stroma and endothelium arise from neural crest cells. The cornea forms the transparent anterior part of the eye, essential for refraction. The multi-layered epithelium ensures barrier protection and contributes to optical clarity through constant regeneration.
4. The optic nerve is derived from which embryonic structure?
a) Neural crest
b) Neural ectoderm of optic stalk
c) Surface ectoderm
d) Mesoderm
Explanation (Answer: b) Neural ectoderm of optic stalk)
The optic nerve develops from the optic stalk, an extension of the diencephalon derived from neural ectoderm. It contains axons of retinal ganglion cells that connect the retina to the brain. Unlike typical peripheral nerves, the optic nerve is part of the central nervous system and is surrounded by meninges.
5. A newborn with congenital blindness due to retinal aplasia has a developmental defect involving:
a) Neural crest
b) Surface ectoderm
c) Neural ectoderm
d) Mesoderm
Explanation (Answer: c) Neural ectoderm)
The retina develops from the neural ectoderm of the optic cup. Retinal aplasia occurs when this neural tissue fails to differentiate properly, resulting in loss of visual photoreceptors and functional blindness. Other ocular tissues like the cornea and lens may remain unaffected, depending on the extent of neural developmental failure.
6. The iris muscles (sphincter and dilator pupillae) are derived from:
a) Mesoderm
b) Neural crest
c) Neural ectoderm
d) Surface ectoderm
Explanation (Answer: c) Neural ectoderm)
Both the sphincter and dilator pupillae muscles are derived from the neural ectoderm of the optic cup. These are unique smooth muscles of ectodermal origin. They control pupillary size and regulate light entry into the eye. This is an exception since most smooth muscles arise from mesodermal origin in the body.
7. The sclera and choroid of the eye primarily develop from:
a) Surface ectoderm
b) Neural crest cells
c) Mesoderm
d) Neural ectoderm
Explanation (Answer: b) Neural crest cells)
The sclera and choroid develop from neural crest cells, which migrate around the optic cup. The sclera forms the dense fibrous protective covering of the eye, while the choroid forms the vascular layer providing oxygen and nutrients to the retina. Defects in neural crest migration may lead to anterior segment dysgenesis.
8. The hyaloid artery in fetal life is responsible for supplying which developing structure?
a) Retina
b) Cornea
c) Lens
d) Optic nerve
Explanation (Answer: c) Lens)
During fetal life, the hyaloid artery, a branch of the ophthalmic artery, supplies the developing lens and vitreous body. It later regresses, leaving behind the central artery of the retina. Persistence of the hyaloid artery after birth may form a vitreous opacity known as Mittendorf’s dot.
9. Coloboma of the iris results from defective closure of which structure?
a) Optic fissure
b) Optic vesicle
c) Lens vesicle
d) Corneal groove
Explanation (Answer: a) Optic fissure)
Coloboma of the iris results from failure of closure of the optic fissure during development of the optic cup. It appears as a keyhole defect in the iris. Depending on the extent, the defect may involve the retina or optic nerve, leading to varying degrees of visual impairment or blindness.
10. A baby is born with anophthalmos (absence of eyes). The most likely embryologic defect involves failure of:
a) Optic vesicle formation
b) Lens placode development
c) Hyaloid vessel regression
d) Optic fissure closure
Explanation (Answer: a) Optic vesicle formation)
Anophthalmos occurs due to complete failure of optic vesicle formation from the forebrain. This prevents induction of the lens placode and subsequent optic cup development. The condition leads to total absence of ocular tissue within the orbit and may be associated with severe cranial or neural tube malformations.
Chapter: Embryology; Topic: Development of Reproductive System; Subtopic: Derivatives of Mesonephric and Paramesonephric Ducts
Keyword Definitions:
• Müllerian duct (Paramesonephric duct): Embryonic structure that develops into the female reproductive tract (uterus, fallopian tubes, upper vagina) and regresses in males.
• Wolffian duct (Mesonephric duct): Embryonic structure that develops into male genital ducts (epididymis, vas deferens, seminal vesicle).
• Prostatic utricle: A small pouch in males derived from the Müllerian duct; homologous to the uterus and vagina.
• Anti-Müllerian hormone (AMH): Hormone secreted by Sertoli cells in males that causes regression of Müllerian ducts.
• Appendix testis: Vestigial Müllerian remnant at the superior pole of the testis.
• Mesonephric tubules: Give rise to efferent ductules of the testes.
Lead Question - 2015
Structure developing from Müllerian duct in males?
a) Seminal vesicle
b) Epididymis
c) Prostatic utricle
d) Ureter
Explanation (Answer: c) Prostatic utricle)
In males, the Müllerian ducts regress under the influence of Anti-Müllerian hormone (AMH) secreted by Sertoli cells. However, small remnants persist, forming the prostatic utricle and appendix testis. The prostatic utricle is a small blind sac opening into the prostatic urethra and represents the male homologue of the uterus and vagina.
1. Which of the following structures is derived from the Müllerian duct in females?
a) Seminal vesicle
b) Fallopian tube
c) Epididymis
d) Prostatic utricle
Explanation (Answer: b) Fallopian tube)
In females, the Müllerian (paramesonephric) ducts develop into the uterine tubes (fallopian tubes), uterus, and upper part of the vagina. This occurs due to the absence of AMH. In males, these ducts regress except for remnants like the appendix testis and prostatic utricle. Their normal fusion forms the midline uterine structure.
2. The mesonephric duct in males develops into which of the following?
a) Uterus
b) Vas deferens
c) Fallopian tube
d) Upper vagina
Explanation (Answer: b) Vas deferens)
The mesonephric (Wolffian) duct develops into male genital ducts including the epididymis, vas deferens, seminal vesicle, and ejaculatory duct. Testosterone secreted by Leydig cells promotes their differentiation, while Anti-Müllerian hormone from Sertoli cells suppresses paramesonephric duct development in males.
3. A small cyst near the prostate in a male child most likely represents a remnant of which embryonic structure?
a) Müllerian duct
b) Mesonephric duct
c) Ureteric bud
d) Allantois
Explanation (Answer: a) Müllerian duct)
A cyst near the prostate represents a prostatic utricle cyst, derived from the Müllerian duct. It is a remnant of embryonic female reproductive tract structures that failed to regress completely in males. Large cysts may cause urinary obstruction or infection but are typically benign and asymptomatic.
4. Which hormone causes regression of the Müllerian ducts in male embryos?
a) Testosterone
b) Anti-Müllerian hormone
c) Estrogen
d) Progesterone
Explanation (Answer: b) Anti-Müllerian hormone)
Anti-Müllerian hormone (AMH) is secreted by Sertoli cells of the fetal testes and induces regression of the Müllerian ducts, preventing the formation of female internal genital organs in males. In its absence, structures such as the uterus and fallopian tubes may persist, leading to Persistent Müllerian Duct Syndrome (PMDS).
5. Persistent Müllerian Duct Syndrome (PMDS) in a male is caused by deficiency of which of the following?
a) Testosterone
b) Anti-Müllerian hormone
c) LH
d) FSH
Explanation (Answer: b) Anti-Müllerian hormone)
PMDS is a rare condition in which Müllerian duct structures (uterus and fallopian tubes) persist in males with normal external genitalia. It occurs due to a deficiency or insensitivity to Anti-Müllerian hormone (AMH) or its receptor. The condition may present as undescended testes or inguinal hernia containing uterine tissue.
6. The epididymis is derived from which embryonic structure?
a) Müllerian duct
b) Mesonephric duct
c) Paramesonephric duct
d) Cloaca
Explanation (Answer: b) Mesonephric duct)
The epididymis originates from the mesonephric duct under the influence of testosterone secreted by Leydig cells. This duct elongates and becomes coiled, forming the epididymal structure. The Müllerian duct, in contrast, regresses in males due to AMH, leaving only small remnants like the appendix testis.
7. In females, failure of fusion of Müllerian ducts leads to which congenital anomaly?
a) Bicornuate uterus
b) Uterine agenesis
c) Vaginal atresia
d) Septate uterus
Explanation (Answer: a) Bicornuate uterus)
A bicornuate uterus occurs when the Müllerian ducts fail to fuse completely during embryonic development, resulting in a uterus with two horns. Other fusion defects include didelphys uterus and septate uterus. These anomalies may cause recurrent miscarriage or infertility, highlighting the importance of normal ductal fusion in female reproductive development.
8. Which of the following male structures represents a Müllerian remnant?
a) Appendix epididymis
b) Appendix testis
c) Vas deferens
d) Seminal vesicle
Explanation (Answer: b) Appendix testis)
The appendix testis is a small pedunculated structure attached to the superior pole of the testis and represents a Müllerian duct remnant. It may undergo torsion, causing acute scrotal pain in children. In contrast, the appendix epididymis is derived from the mesonephric duct, not the Müllerian duct.
9. Which of the following is NOT derived from the Müllerian duct?
a) Uterus
b) Fallopian tubes
c) Upper vagina
d) Labia majora
Explanation (Answer: d) Labia majora)
The labia majora are derived from the genital swellings, not the Müllerian ducts. The Müllerian ducts give rise to the fallopian tubes, uterus, and the upper part of the vagina. The lower vagina develops from the urogenital sinus, which fuses with the Müllerian ducts during embryogenesis.
10. A male newborn with cryptorchidism and uterus-like structure in the pelvis likely has:
a) Persistent Müllerian Duct Syndrome
b) Klinefelter syndrome
c) Androgen insensitivity syndrome
d) Testicular feminization
Explanation (Answer: a) Persistent Müllerian Duct Syndrome)
Persistent Müllerian Duct Syndrome (PMDS) is seen in males (46, XY) with normal external genitalia but persistent Müllerian derivatives due to lack of Anti-Müllerian hormone (AMH) or receptor defects. It may present with cryptorchidism or inguinal hernia containing a uterus or fallopian tube. Testosterone levels are usually normal in such cases.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Development of Venous System
Keyword Definitions:
• Superior vena cava (SVC): Large systemic vein returning deoxygenated blood from the head, neck, and upper limbs to the right atrium.
• Anterior cardinal veins: Paired embryonic veins that drain the cranial portion of the embryo.
• Common cardinal veins: Short venous trunks connecting anterior and posterior cardinal veins to the sinus venosus.
• Subcardinal veins: Veins forming part of the inferior vena cava, renal, and gonadal veins.
• Supracardinal veins: Veins that form the azygos and hemiazygos systems.
• Sinus venosus: Primitive venous chamber that becomes incorporated into the right atrium during cardiac development.
Lead Question - 2015
Superior vena cava develops from -
a) Right anterior cardinal vein
b) Left anterior cardinal vein
c) Left common cardinal vein
d) Right subcardinal vein
Explanation (Answer: a) Right anterior cardinal vein)
The superior vena cava (SVC) develops from the right anterior cardinal vein and the right common cardinal vein. The left anterior cardinal vein largely regresses, with its remnant forming part of the left brachiocephalic vein. The SVC drains blood from the head, neck, and upper limbs into the right atrium. Abnormal persistence of the left anterior cardinal vein can result in a double SVC anomaly.
1. The left brachiocephalic vein develops from which embryonic structure?
a) Right anterior cardinal vein
b) Left posterior cardinal vein
c) Left anterior cardinal vein
d) Subcardinal vein
Explanation (Answer: c) Left anterior cardinal vein)
The left brachiocephalic vein develops from the left anterior cardinal vein and an anastomosis between the right and left anterior cardinal veins. This allows blood from the left head and upper limb to drain into the right-sided SVC. Regression of the left common cardinal vein and persistence of this connection create the left brachiocephalic vein.
2. Which of the following embryonic veins forms the azygos vein?
a) Right supracardinal vein
b) Right subcardinal vein
c) Right posterior cardinal vein
d) Left anterior cardinal vein
Explanation (Answer: a) Right supracardinal vein)
The azygos vein develops from the right supracardinal vein. This vein drains the posterior thoracic wall and joins the superior vena cava near its termination. The left supracardinal vein forms the hemiazygos vein, while posterior cardinal veins regress and are replaced by the supracardinal and subcardinal systems during embryonic development.
3. The inferior vena cava (IVC) is formed from all except:
a) Hepatic veins
b) Subcardinal veins
c) Posterior cardinal veins
d) Anterior cardinal veins
Explanation (Answer: d) Anterior cardinal veins)
The inferior vena cava (IVC) is formed from the hepatic veins, subcardinal veins, supracardinal veins, and posterior cardinal veins, but not from the anterior cardinal veins. The anterior cardinal veins contribute to the superior venous system, including the internal jugular veins and the superior vena cava, not the IVC.
4. Which embryonic vein forms the internal jugular veins?
a) Anterior cardinal vein
b) Posterior cardinal vein
c) Subcardinal vein
d) Common cardinal vein
Explanation (Answer: a) Anterior cardinal vein)
The anterior cardinal veins form the internal jugular veins, which drain the cranial part of the embryo. The right anterior cardinal vein and common cardinal vein later form the superior vena cava, while the left anterior cardinal vein contributes to the left brachiocephalic vein through anastomotic connections.
5. Which of the following anomalies results from persistence of the left anterior cardinal vein?
a) Double superior vena cava
b) Absent inferior vena cava
c) Azygos continuation
d) Persistent ductus venosus
Explanation (Answer: a) Double superior vena cava)
Persistence of the left anterior cardinal vein results in the formation of a double superior vena cava. Normally, this vein regresses, and its blood drains into the right side through the left brachiocephalic vein. When it persists, a second SVC is formed on the left, typically draining into the coronary sinus.
6. The right common cardinal vein contributes to which adult structure?
a) Coronary sinus
b) Superior vena cava
c) Inferior vena cava
d) Azygos vein
Explanation (Answer: b) Superior vena cava)
The right common cardinal vein, along with the right anterior cardinal vein, forms the superior vena cava. The left common cardinal vein and the left sinus horn form the coronary sinus. The common cardinal veins act as the final venous channels draining into the primitive sinus venosus during embryogenesis.
7. The coronary sinus develops from which embryonic structure?
a) Right anterior cardinal vein
b) Left common cardinal vein
c) Left posterior cardinal vein
d) Right subcardinal vein
Explanation (Answer: b) Left common cardinal vein)
The coronary sinus develops from the left common cardinal vein and the left sinus horn. This structure persists in the adult heart as the main venous channel draining the myocardium into the right atrium. The regression of the left-sided systemic venous channels leaves the coronary sinus as a vestige of the left venous system.
8. A 3-year-old child presents with cyanosis and venous drainage from left upper limb directly into the coronary sinus. The cause is:
a) Persistent left anterior cardinal vein
b) Absent right anterior cardinal vein
c) Persistent left common cardinal vein
d) Absent right common cardinal vein
Explanation (Answer: a) Persistent left anterior cardinal vein)
Persistence of the left anterior cardinal vein leads to venous drainage from the left upper limb and head directly into the coronary sinus. This anomaly produces a left-sided superior vena cava. It is usually asymptomatic but may complicate cardiac catheterization or pacemaker insertion due to the altered venous route.
9. The azygos and hemiazygos veins develop from:
a) Posterior cardinal veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: c) Supracardinal veins)
The supracardinal veins develop to replace the posterior cardinal veins and form the azygos (right) and hemiazygos (left) veins. These veins drain the posterior thoracic wall and intercostal spaces. The posterior cardinal veins regress except for their caudal parts, which persist as the common iliac veins.
10. A newborn has absence of superior vena cava on the right, with drainage of head and neck veins into the coronary sinus. This condition is due to:
a) Regression of right anterior cardinal vein
b) Regression of left anterior cardinal vein
c) Persistence of right subcardinal vein
d) Persistence of left supracardinal vein
Explanation (Answer: a) Regression of right anterior cardinal vein)
Absence of the right superior vena cava occurs due to regression of the right anterior cardinal vein and persistence of the left anterior cardinal vein, which drains into the coronary sinus. This creates a left-sided superior vena cava, an uncommon venous anomaly seen in some congenital heart defects.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Development of Venous System
Keyword Definitions:
• Posterior cardinal veins: Paired embryonic veins that drain the body wall and lower part of the embryo; they are replaced by subcardinal and supracardinal veins later.
• Common iliac veins: Veins formed from the caudal portions of the posterior cardinal veins.
• Subcardinal veins: Veins forming parts of the inferior vena cava, renal, and gonadal veins.
• Supracardinal veins: Veins forming azygos and hemiazygos systems.
• Anterior cardinal veins: Form internal jugular and superior vena cava.
• Common cardinal veins: Short segments draining into the sinus venosus, forming part of the right atrium.
Lead Question - 2015
Posterior cardinal vein develops into -
a) Common iliac vein
b) Superior vena cava
c) Internal jugular vein
d) External jugular vein
Explanation (Answer: a) Common iliac vein)
The posterior cardinal veins are embryonic veins that initially drain the lower part of the body. Most of them regress during development, but their caudal portions persist as the common iliac veins. They are later replaced by the subcardinal and supracardinal systems, which contribute to the formation of the inferior vena cava and azygos veins.
1. The superior vena cava develops from which embryonic vein?
a) Anterior cardinal vein
b) Posterior cardinal vein
c) Subcardinal vein
d) Supracardinal vein
Explanation (Answer: a) Anterior cardinal vein)
The superior vena cava develops from the right anterior cardinal vein and the right common cardinal vein. The left anterior cardinal vein regresses except for its upper part, which forms the left brachiocephalic vein. The posterior cardinal veins do not contribute to the superior vena cava in the adult.
2. Which part of the inferior vena cava is derived from the posterior cardinal veins?
a) Hepatic segment
b) Prerenal segment
c) Renal segment
d) Postrenal segment
Explanation (Answer: d) Postrenal segment)
The postrenal segment of the inferior vena cava develops from the right supracardinal and posterior cardinal veins. The hepatic segment arises from the hepatic veins, the prerenal from the right subcardinal vein, and the renal from the subcardinal–supracardinal anastomosis. Thus, posterior cardinal veins contribute mainly to the lower (postrenal) IVC and common iliac veins.
3. Azygos vein develops from which embryonic vein?
a) Subcardinal vein
b) Supracardinal vein
c) Posterior cardinal vein
d) Common cardinal vein
Explanation (Answer: b) Supracardinal vein)
The azygos vein develops from the right supracardinal vein and drains the posterior thoracic wall. The left supracardinal vein forms the hemiazygos vein. The posterior cardinal veins largely regress, with only their caudal portions persisting as common iliac veins. The supracardinal system replaces the posterior cardinal veins in most regions.
4. Which embryonic structure gives rise to the renal veins?
a) Posterior cardinal veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: b) Subcardinal veins)
The renal veins develop from the subcardinal veins and the subcardinal–supracardinal anastomosis. These veins also form the gonadal veins and a part of the inferior vena cava. The posterior cardinal veins play only a minor transient role in the early embryonic venous drainage and are later replaced by subcardinal and supracardinal veins.
5. The internal jugular vein develops from which embryonic vein?
a) Anterior cardinal vein
b) Posterior cardinal vein
c) Subcardinal vein
d) Supracardinal vein
Explanation (Answer: a) Anterior cardinal vein)
The internal jugular veins develop from the anterior cardinal veins, which drain the cranial part of the embryo. The left anterior cardinal vein contributes to the left brachiocephalic vein, while the right forms part of the superior vena cava. Posterior cardinal veins drain the caudal regions and are not involved in jugular formation.
6. A neonate with an absent inferior vena cava below the renal veins likely has developmental failure of which embryonic structure?
a) Hepatic veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: c) Supracardinal veins)
The supracardinal veins form the postrenal segment of the inferior vena cava. Failure of their development results in absence of IVC below the renal veins. In such cases, venous return from the lower limbs occurs through the azygos and hemiazygos systems, compensating for the absent lower IVC segment.
7. Which embryonic vein forms the hemiazygos vein?
a) Left supracardinal vein
b) Right subcardinal vein
c) Left posterior cardinal vein
d) Right common cardinal vein
Explanation (Answer: a) Left supracardinal vein)
The hemiazygos vein develops from the left supracardinal vein. It drains the lower left posterior thoracic wall and crosses to join the azygos vein. The right supracardinal vein forms the azygos system, while the posterior cardinal veins regress, except for their caudal ends forming common iliac veins.
8. The left brachiocephalic vein is formed by an anastomosis between:
a) Subcardinal veins
b) Anterior cardinal veins
c) Posterior cardinal veins
d) Common cardinal veins
Explanation (Answer: b) Anterior cardinal veins)
The left brachiocephalic vein forms from a transverse anastomosis between the left and right anterior cardinal veins. Blood from the left head and neck drains through this vein into the right anterior cardinal system, which forms the superior vena cava. This anastomosis compensates for regression of the caudal part of the left anterior cardinal vein.
9. Which of the following venous anomalies occurs due to persistence of the left anterior cardinal vein?
a) Double superior vena cava
b) Absent azygos vein
c) Interrupted IVC
d) Persistent ductus venosus
Explanation (Answer: a) Double superior vena cava)
Persistence of the left anterior cardinal vein results in a double superior vena cava. Normally, the caudal part of this vein regresses during development. When it persists, venous blood from the left side drains into the coronary sinus rather than joining the right superior vena cava, creating a dual drainage system.
10. A 6-year-old boy has congenital absence of common iliac veins. Which embryonic structure failed to develop properly?
a) Posterior cardinal veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: a) Posterior cardinal veins)
The common iliac veins develop from the caudal portions of the posterior cardinal veins. Failure of their development leads to congenital absence of these veins, resulting in alternate pelvic venous drainage through collateral pathways. The posterior cardinal system is transient but crucial for forming iliac and early systemic venous segments.
Chapter: Embryology; Topic: Development of Endocrine System; Subtopic: Development of Pituitary Gland
Keyword Definitions:
• Rathke’s pouch: An ectodermal outpouching from the roof of the stomodeum forming the anterior pituitary (adenohypophysis).
• Infundibulum: A neuroectodermal downward extension from the diencephalon forming the posterior pituitary (neurohypophysis).
• Adenohypophysis: Anterior lobe of the pituitary that secretes hormones like prolactin, GH, and ACTH.
• Neurohypophysis: Posterior lobe of pituitary storing ADH and oxytocin from hypothalamic neurons.
• Tuber cinereum: Area of hypothalamus between optic chiasma and mammillary bodies controlling pituitary function.
• Prolactin: Hormone secreted by lactotrophs of adenohypophysis that stimulates milk production in females.
Lead Question - 2015
Prolactin secreting gland develops from -
a) Infundibulum
b) Rathke's pouch
c) Tuber cinereum
d) 3rd ventricle
Explanation (Answer: b) Rathke’s pouch)
The anterior pituitary (adenohypophysis), which secretes prolactin, develops from the Rathke’s pouch — an ectodermal diverticulum from the roof of the primitive mouth (stomodeum). The posterior lobe (neurohypophysis) originates from the infundibulum of the diencephalon. The gland later differentiates into secretory cells producing prolactin, GH, ACTH, and other trophic hormones.
1. The anterior lobe of the pituitary gland is derived from which embryonic germ layer?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neuroectoderm
Explanation (Answer: c) Ectoderm)
The adenohypophysis (anterior pituitary) originates from oral ectoderm of Rathke’s pouch. This ectodermal tissue grows upward from the roof of the primitive mouth and later detaches to form the anterior lobe. In contrast, the neurohypophysis arises from neuroectoderm of the diencephalon, forming a neural connection to the hypothalamus.
2. The posterior pituitary develops from which of the following structures?
a) Rathke’s pouch
b) Infundibulum
c) Tuber cinereum
d) Roof of stomodeum
Explanation (Answer: b) Infundibulum)
The neurohypophysis or posterior pituitary develops from the infundibular process, a downward projection of neuroectoderm from the diencephalon. It remains connected to the hypothalamus via the infundibular stalk and stores oxytocin and vasopressin, which are synthesized in the supraoptic and paraventricular nuclei of the hypothalamus.
3. Which of the following cells secrete prolactin in the anterior pituitary?
a) Somatotrophs
b) Corticotrophs
c) Lactotrophs
d) Thyrotrophs
Explanation (Answer: c) Lactotrophs)
Lactotrophs (mammotrophs) are the cells in the adenohypophysis responsible for prolactin secretion. Prolactin stimulates breast development and milk secretion. Its secretion is tonically inhibited by dopamine from the hypothalamus. During pregnancy and lactation, estrogen and TRH increase prolactin synthesis and release from these specialized cells.
4. Which of the following hormones is NOT secreted by the anterior pituitary?
a) ACTH
b) GH
c) Vasopressin
d) TSH
Explanation (Answer: c) Vasopressin)
Vasopressin (ADH) is secreted by the posterior pituitary (neurohypophysis), not the anterior lobe. The anterior pituitary secretes six major hormones—GH, ACTH, TSH, FSH, LH, and prolactin—all derived from ectoderm of Rathke’s pouch. ADH is synthesized in the hypothalamus and only stored in the posterior pituitary.
5. A patient with pituitary adenoma involving lactotrophs would most likely present with:
a) Hypothyroidism
b) Amenorrhea and galactorrhea
c) Cushing’s syndrome
d) Acromegaly
Explanation (Answer: b) Amenorrhea and galactorrhea)
Prolactin-secreting pituitary adenoma (prolactinoma) causes hyperprolactinemia leading to amenorrhea, galactorrhea, and infertility in females, and decreased libido in males. Prolactin suppresses GnRH secretion, reducing FSH and LH levels. Dopamine agonists like bromocriptine or cabergoline are used for medical management of prolactinomas.
6. The pituitary gland is located within which bony structure?
a) Sphenoid sinus
b) Hypophyseal fossa
c) Optic canal
d) Foramen magnum
Explanation (Answer: b) Hypophyseal fossa)
The pituitary gland resides in the hypophyseal fossa of the sella turcica in the sphenoid bone. This bony cavity protects the gland and is covered superiorly by the diaphragma sellae. The optic chiasma lies anterior and superior to it, making it prone to compression in pituitary tumors causing visual disturbances.
7. Which of the following statements about Rathke’s pouch is true?
a) It is derived from endoderm
b) Gives rise to posterior pituitary
c) It is an upward growth from stomodeum
d) It remains connected to the hypothalamus
Explanation (Answer: c) It is an upward growth from stomodeum)
Rathke’s pouch is an upward ectodermal outpouching from the roof of the stomodeum (primitive mouth) that forms the anterior lobe of the pituitary gland. It later detaches from the oral cavity and fuses with the downward-growing infundibulum from the diencephalon to form the complete pituitary gland.
8. A child with craniopharyngioma has a tumor derived from remnants of:
a) Infundibulum
b) Rathke’s pouch
c) Pineal gland
d) Optic chiasma
Explanation (Answer: b) Rathke’s pouch)
Craniopharyngioma is a benign tumor arising from remnants of Rathke’s pouch. It commonly occurs in children and young adults, presenting with headaches, visual disturbances, and growth retardation due to compression of the optic chiasma and pituitary gland. It contains calcifications and cystic areas with cholesterol-rich fluid.
9. Which hypothalamic nucleus is primarily responsible for prolactin inhibition?
a) Supraoptic nucleus
b) Paraventricular nucleus
c) Arcuate nucleus
d) Mammillary nucleus
Explanation (Answer: c) Arcuate nucleus)
The arcuate nucleus of the hypothalamus secretes dopamine (prolactin-inhibiting hormone) that inhibits prolactin secretion from lactotrophs of the anterior pituitary. Damage to this nucleus or dopaminergic pathways results in hyperprolactinemia. Dopamine agonists, such as bromocriptine, restore prolactin control in such cases.
10. A 45-year-old woman presents with bitemporal hemianopia and hyperprolactinemia. MRI shows a sellar mass. Which structure is compressed?
a) Optic chiasma
b) Internal capsule
c) Corpus callosum
d) Hypothalamus
Explanation (Answer: a) Optic chiasma)
A pituitary macroadenoma enlarging superiorly from the sella turcica compresses the optic chiasma, producing bitemporal hemianopia. It may also cause hormonal imbalances, including hyperprolactinemia due to lactotroph adenoma. Surgical decompression via trans-sphenoidal approach is the preferred treatment in such cases.
Chapter: Embryology; Topic: Development of Reproductive System; Subtopic: Origin and Function of Sertoli Cells
Keyword Definitions:
• Sertoli cells: Tall supporting cells in seminiferous tubules that nourish developing sperm and form the blood-testis barrier.
• Germinal epithelium: Layer of epithelial cells lining the primitive gonadal ridge giving rise to Sertoli and follicular cells.
• Primordial germ cells: Cells that give rise to spermatozoa and ova.
• Seminiferous tubules: Tubules within the testes where spermatogenesis occurs.
• Genital ridge: Embryonic structure forming the gonads.
• Genital tubercle: Embryonic swelling giving rise to external genitalia.
Lead Question - 2015
Sertoli cells are derived from -
a) Genital tubercle
b) Genital swelling
c) Primordial germ cells
d) Germinal epithelium
Explanation (Answer: d) Germinal epithelium)
Sertoli cells originate from the germinal epithelium (coelomic epithelium) of the developing gonadal ridge. They differentiate within seminiferous cords of the testis and play a vital role in spermatogenesis by providing nourishment and structural support. They also secrete Anti-Müllerian hormone (AMH), crucial for regression of Müllerian ducts in males.
1. Which of the following hormones is secreted by Sertoli cells?
a) Testosterone
b) Inhibin
c) LH
d) FSH
Explanation (Answer: b) Inhibin)
Sertoli cells secrete inhibin, a peptide hormone that provides negative feedback to the anterior pituitary to regulate FSH secretion. They also produce Androgen Binding Protein (ABP) to concentrate testosterone in seminiferous tubules, supporting spermatogenesis. Leydig cells, not Sertoli cells, secrete testosterone under LH stimulation.
2. The primary function of Sertoli cells in the seminiferous tubules is:
a) Secretion of testosterone
b) Nourishment and support of germ cells
c) Formation of seminal plasma
d) Production of sperm motility factors
Explanation (Answer: b) Nourishment and support of germ cells)
Sertoli cells are essential “nurse” cells that nourish, support, and protect developing spermatogenic cells. They form tight junctions creating the blood-testis barrier and phagocytose residual cytoplasm from spermatids. They also secrete inhibin, AMH, and ABP, maintaining a suitable microenvironment for spermatogenesis under FSH influence.
3. Which embryonic structure gives rise to Leydig cells in the testis?
a) Germinal epithelium
b) Mesenchyme of genital ridge
c) Wolffian duct
d) Paramesonephric duct
Explanation (Answer: b) Mesenchyme of genital ridge)
Leydig cells, the interstitial cells of the testis, originate from the mesenchyme of the genital ridge. They begin secreting testosterone around the 8th week of development, which is essential for differentiation of the male reproductive tract and external genitalia. Sertoli cells, by contrast, arise from the germinal epithelium.
4. Which hormone induces Sertoli cells to secrete Androgen Binding Protein (ABP)?
a) LH
b) FSH
c) Testosterone
d) Prolactin
Explanation (Answer: b) FSH)
FSH (Follicle Stimulating Hormone) acts on Sertoli cells, stimulating them to produce Androgen Binding Protein (ABP) that binds and concentrates testosterone in seminiferous tubules. This high local testosterone concentration is critical for spermatogenesis. LH acts on Leydig cells to produce testosterone, which synergizes with FSH in this process.
5. A newborn male with persistent Müllerian duct structures likely has a defect in secretion of:
a) Testosterone
b) Anti-Müllerian hormone
c) Inhibin
d) FSH
Explanation (Answer: b) Anti-Müllerian hormone)
Sertoli cells secrete Anti-Müllerian hormone (AMH) during fetal life, which causes regression of the paramesonephric (Müllerian) ducts. Deficiency or absence of AMH results in Persistent Müllerian Duct Syndrome (PMDS), where male individuals have remnants of uterus and fallopian tubes despite normal male external genitalia and karyotype (46, XY).
6. Which of the following cells form the blood-testis barrier?
a) Spermatogonia
b) Sertoli cells
c) Leydig cells
d) Myoid cells
Explanation (Answer: b) Sertoli cells)
Sertoli cells form the blood-testis barrier through tight junctions between adjacent cells, dividing the seminiferous tubule into basal and adluminal compartments. This barrier protects developing germ cells from autoimmune attack by preventing exposure of sperm antigens to the immune system while allowing selective nutrient exchange.
7. Damage to Sertoli cells would primarily affect which process?
a) Testosterone synthesis
b) Spermatogenesis
c) Epididymal transport
d) Seminal fluid secretion
Explanation (Answer: b) Spermatogenesis)
Sertoli cells are vital for spermatogenesis as they provide physical and nutritional support for germ cells, form the blood-testis barrier, and secrete growth factors essential for sperm development. Their injury disrupts the seminiferous epithelium, halting sperm maturation despite normal testosterone levels from Leydig cells.
8. A 22-year-old male presents with infertility despite normal testosterone. Which defect could explain this finding?
a) Dysfunction of Sertoli cells
b) Leydig cell hyperplasia
c) Pituitary tumor
d) Hypothalamic lesion
Explanation (Answer: a) Dysfunction of Sertoli cells)
Normal testosterone with infertility suggests defective Sertoli cell function. Sertoli cells support spermatogenesis, form the blood-testis barrier, and secrete ABP and inhibin. Their dysfunction impairs sperm maturation and leads to non-obstructive azoospermia. Leydig cells remain unaffected, explaining normal testosterone production.
9. Which of the following pairs is correctly matched?
a) Leydig cells – Blood-testis barrier
b) Sertoli cells – Androgen binding protein
c) Spermatogonia – Testosterone synthesis
d) Germinal epithelium – LH secretion
Explanation (Answer: b) Sertoli cells – Androgen binding protein)
Sertoli cells produce Androgen Binding Protein (ABP) in response to FSH stimulation. ABP binds testosterone and maintains high intratubular concentration necessary for spermatogenesis. Leydig cells synthesize testosterone, while spermatogonia are developing germ cells that rely on the Sertoli cell environment for maturation.
10. In a male infant with XY karyotype and persistence of Müllerian ducts, which gene or hormone deficiency is most likely?
a) AMH deficiency
b) Testosterone deficiency
c) LH receptor mutation
d) FSH receptor mutation
Explanation (Answer: a) AMH deficiency)
Persistence of Müllerian structures (uterus and fallopian tubes) in a genetic male indicates Anti-Müllerian hormone (AMH) deficiency or insensitivity. AMH, produced by fetal Sertoli cells, normally induces Müllerian duct regression. Its absence leads to Persistent Müllerian Duct Syndrome, despite normal androgen and external genital development.
Chapter: Embryology; Topic: Development of Heart; Subtopic: Interatrial Septum and Fossa Ovalis
Keyword Definitions:
• Fossa ovalis: A depression in the interatrial septum of the right atrium, representing the closed foramen ovale of the fetal heart.
• Limbus fossa ovalis (Annulus ovalis): Raised margin surrounding the fossa ovalis, derived from the septum secundum.
• Septum primum: The first septum growing downward to separate the primitive atrium.
• Septum secundum: A crescent-shaped fold that overlaps the foramen ovale and forms the limbus.
• Foramen ovale: A fetal opening between the atria allowing blood to bypass the lungs.
• Interatrial septum: Wall separating right and left atria, formed from both septum primum and secundum.
Lead Question - 2015
False about limbus fossa ovalis -
a) Situated above fossa ovalis
b) In right atrium
c) Derived from septum primum
d) Also called Annulus ovalis
Explanation (Answer: c) Derived from septum primum)
The limbus fossa ovalis, also called the annulus ovalis, is a raised ridge located around the upper margin of the fossa ovalis in the right atrium. It is derived from the septum secundum, not from the septum primum. The septum primum forms the floor of the fossa ovalis itself.
1. The fossa ovalis in the adult heart is a remnant of which embryonic structure?
a) Foramen primum
b) Septum secundum
c) Foramen ovale
d) Ductus arteriosus
Explanation (Answer: c) Foramen ovale)
The fossa ovalis in the adult right atrium represents the closed foramen ovale of the fetal heart. During fetal life, the foramen ovale allowed blood to pass from the right atrium to the left atrium, bypassing pulmonary circulation. After birth, it closes functionally and later anatomically to form the fossa ovalis.
2. The upper border of the fossa ovalis is known as:
a) Septum primum
b) Septum intermedium
c) Limbus fossa ovalis
d) Crista terminalis
Explanation (Answer: c) Limbus fossa ovalis)
The limbus fossa ovalis forms the prominent upper margin of the fossa ovalis in the right atrium. It is derived from the septum secundum. It appears as a raised border surrounding the fossa, demarcating the area of embryonic fusion of the septa that separated the two atria during development.
3. In which chamber of the heart is the fossa ovalis located?
a) Left atrium
b) Right atrium
c) Left ventricle
d) Right ventricle
Explanation (Answer: b) Right atrium)
The fossa ovalis is located in the right atrium on the interatrial septum. It is visible as a shallow oval depression below the limbus. On the left atrial side, it corresponds to a slight ridge. The fossa ovalis marks the site of the closed foramen ovale, a vital fetal shunt between the atria.
4. Which structure forms the floor of the fossa ovalis?
a) Septum secundum
b) Septum primum
c) Endocardial cushions
d) Sinus venosus
Explanation (Answer: b) Septum primum)
The floor of the fossa ovalis is derived from the septum primum. During fetal life, the septum primum acted as a valve over the foramen ovale. After birth, increased left atrial pressure pushes it against the septum secundum, leading to closure and eventual fusion, forming the interatrial septum in the adult heart.
5. A 2-year-old child presents with shortness of breath and cyanosis. Echocardiography reveals a patent foramen ovale. The defect is due to failure of fusion between:
a) Septum primum and endocardial cushions
b) Septum secundum and septum primum
c) Septum primum and interventricular septum
d) Septum secundum and sinus venosus
Explanation (Answer: b) Septum secundum and septum primum)
A patent foramen ovale results from the failure of fusion between the septum primum and septum secundum after birth. This causes persistence of interatrial communication, leading to shunting of blood and cyanosis. Unlike ASD, it is a functional defect, not a true septal deficiency.
6. Which of the following correctly represents the embryological derivation of the limbus fossa ovalis?
a) Septum primum
b) Septum secundum
c) Endocardial cushions
d) Common atrial wall
Explanation (Answer: b) Septum secundum)
The limbus fossa ovalis is derived from the septum secundum, which forms the thickened superior rim of the fossa ovalis in the right atrium. In contrast, the septum primum forms the floor of the fossa. This structure demarcates the site of the embryonic foramen ovale closure postnatally.
7. In fetal circulation, blood passes from right atrium to left atrium through:
a) Ductus venosus
b) Foramen ovale
c) Ductus arteriosus
d) Sinus venosus
Explanation (Answer: b) Foramen ovale)
In the fetus, oxygenated blood from the placenta enters the right atrium and passes through the foramen ovale into the left atrium, bypassing the nonfunctional lungs. After birth, rising left atrial pressure forces closure of the foramen, which later becomes the fossa ovalis in the adult heart.
8. A patient with an atrial septal defect has a defect in which structure?
a) Septum primum
b) Septum secundum
c) Both septum primum and secundum
d) Interventricular septum
Explanation (Answer: c) Both septum primum and secundum)
Atrial septal defects (ASD) often occur due to incomplete development or alignment of the septum primum and septum secundum. This results in an interatrial communication causing left-to-right shunt and increased pulmonary blood flow. Common types include ostium secundum and ostium primum defects, depending on location and extent of the gap.
9. In which condition does the foramen ovale remain patent, but the septa are normally developed?
a) Atrial septal defect
b) Patent foramen ovale
c) Endocardial cushion defect
d) Ventricular septal defect
Explanation (Answer: b) Patent foramen ovale)
In patent foramen ovale (PFO), the septum primum and septum secundum fail to fuse completely, even though both are structurally normal. This persistence allows potential right-to-left shunt under pressure changes, sometimes leading to paradoxical embolism without true septal tissue deficiency, distinguishing it from ASD.
10. A 5-year-old with a history of recurrent respiratory infections is found to have left-to-right shunt due to ostium secundum defect. The likely embryologic cause is:
a) Excessive resorption of septum primum
b) Underdevelopment of septum secundum
c) Both a and b
d) Fusion of septum primum and secundum
Explanation (Answer: c) Both a and b)
An ostium secundum ASD commonly results from excessive resorption of septum primum or underdevelopment of septum secundum. This leads to a persistent opening in the interatrial septum, causing a left-to-right shunt, increased pulmonary flow, and predisposition to respiratory infections and heart failure in children.
Chapter: Embryology; Topic: Development of Head and Neck; Subtopic: Pharyngeal Arches and Their Derivatives
Keyword Definitions:
• Pharyngeal arches: Embryonic swellings on the lateral sides of the head and neck that give rise to various head and neck structures.
• Meckel’s cartilage: Cartilage of the first pharyngeal arch that forms malleus and incus.
• Reichert’s cartilage: Cartilage of the second pharyngeal arch forming stapes and styloid process.
• Malleus and Incus: Two middle ear ossicles derived from the first arch.
• Stapes: Middle ear ossicle derived from the second arch.
• Mandibular arch: Another name for the first pharyngeal arch.
Lead Question - 2015
Malleus and incus are derived from?
a) 1st Arch
b) 2nd Arch
c) 3rd Arch
d) 4th Arch
Explanation (Answer: a) 1st Arch
The malleus and incus are derived from Meckel’s cartilage of the first pharyngeal (mandibular) arch. This arch also contributes to the maxilla, mandible, and muscles of mastication. The stapes and styloid process originate from Reichert’s cartilage of the second arch, while the third and fourth arches form parts of the hyoid and laryngeal cartilages.
1. Which pharyngeal arch gives rise to the stapes and styloid process?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation (Answer: b) Second arch)
The second pharyngeal arch, also called the hyoid arch, gives rise to the stapes, styloid process, lesser horn and upper part of the hyoid bone. Its cartilage is called Reichert’s cartilage. Muscles derived from this arch include muscles of facial expression supplied by the facial nerve (cranial nerve VII).
2. The mandible develops from which pharyngeal arch?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation (Answer: a) First arch)
The mandible arises from the first pharyngeal arch through ossification of Meckel’s cartilage. This arch is innervated by the mandibular division of the trigeminal nerve (V3). Other derivatives include the maxilla, malleus, incus, and muscles of mastication, making it the most significant arch in facial development.
3. A congenital anomaly involving the stapes and styloid process suggests a defect in which embryonic structure?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation (Answer: b) Second pharyngeal arch)
The second pharyngeal arch (Reichert’s cartilage) forms the stapes, styloid process, and part of the hyoid bone. A defect in this arch can cause abnormalities in hearing and neck bone formation. It is innervated by the facial nerve, which also supplies its derived muscles of facial expression.
4. Which of the following muscles is derived from the first pharyngeal arch?
a) Stylopharyngeus
b) Buccinator
c) Tensor tympani
d) Cricothyroid
Explanation (Answer: c) Tensor tympani)
The tensor tympani muscle arises from the first pharyngeal arch. It functions to dampen loud sounds by tensing the tympanic membrane. Other muscles of this arch include muscles of mastication, mylohyoid, and tensor veli palatini, all supplied by the mandibular nerve (V3), a branch of the trigeminal nerve.
5. A newborn with congenital absence of the stapes likely has a developmental defect involving:
a) Reichert’s cartilage
b) Meckel’s cartilage
c) Fourth arch cartilage
d) Thyroid cartilage
Explanation (Answer: a) Reichert’s cartilage)
Reichert’s cartilage is the cartilage of the second pharyngeal arch. It gives rise to the stapes, styloid process, stylohyoid ligament, and lesser horn of the hyoid bone. Any defect or interruption in its development results in congenital stapes absence or middle ear deformities leading to conductive hearing loss.
6. The third pharyngeal arch gives rise to which of the following structures?
a) Greater horn of hyoid bone
b) Styloid process
c) Thyroid cartilage
d) Mandible
Explanation (Answer: a) Greater horn of hyoid bone)
The third pharyngeal arch forms the greater horn and lower part of the hyoid bone and gives rise to the stylopharyngeus muscle, supplied by the glossopharyngeal nerve (cranial nerve IX). It plays a key role in forming parts of the pharyngeal wall and supports the tongue and laryngeal framework.
7. A patient presents with abnormal facial expressions and maldevelopment of the styloid process. The affected cranial nerve is:
a) Trigeminal nerve
b) Facial nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation (Answer: b) Facial nerve)
The facial nerve (cranial nerve VII) innervates structures derived from the second pharyngeal arch. These include muscles of facial expression and derivatives of Reichert’s cartilage like the styloid process. Hence, damage or developmental anomalies affecting this arch result in facial muscle weakness or asymmetry.
8. Which of the following cartilages is derived from the fourth pharyngeal arch?
a) Cricoid cartilage
b) Thyroid cartilage
c) Arytenoid cartilage
d) Epiglottic cartilage
Explanation (Answer: b) Thyroid cartilage)
The fourth and sixth pharyngeal arches together form most of the laryngeal cartilages. The thyroid cartilage arises mainly from the fourth arch, while the cricoid, arytenoid, and corniculate cartilages develop from the sixth. The fourth arch is supplied by the superior laryngeal branch of the vagus nerve.
9. The muscles of mastication develop from which pharyngeal arch?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation (Answer: a) First arch)
Muscles of mastication—masseter, temporalis, and pterygoids—arise from the first pharyngeal (mandibular) arch. They are supplied by the mandibular branch of the trigeminal nerve (V3). This arch also contributes to Meckel’s cartilage, from which the malleus and incus develop, forming essential components of the middle ear.
10. A 3-year-old child presents with conductive hearing loss. Imaging reveals malformed malleus and incus. Which embryonic origin is implicated?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation (Answer: a) First pharyngeal arch)
Malformed malleus and incus indicate developmental defects of the first pharyngeal (mandibular) arch. Meckel’s cartilage of this arch forms these ossicles. The associated cranial nerve is the mandibular division of the trigeminal nerve, and defects often result in both auditory and jaw malformations in affected children.
Chapter: Embryology; Topic: Fetal Circulation; Subtopic: Fate of Umbilical Vessels After Birth
Key Definitions:
• Umbilical arteries: Paired vessels carrying deoxygenated blood from the fetus to the placenta during intrauterine life.
• Umbilical vein: A single vessel that carries oxygenated blood from the placenta to the fetus.
• Ligamentum arteriosum: The fibrous remnant of the ductus arteriosus connecting the pulmonary artery to the aortic arch.
• Medial umbilical ligament: The postnatal fibrous remnant of the distal portion of the umbilical arteries that runs along the inner abdominal wall.
Lead Question (NEET PG 2015):
1. Remnant of umbilical artery:
a) Ligamentum arteriosum
b) Ligament teres
c) Ligamentum venosum
d) Medial umbilical ligament
Answer: d) Medial umbilical ligament
Explanation: The umbilical arteries carry deoxygenated blood from the fetus to the placenta. After birth, the distal parts of these arteries close and form the medial umbilical ligaments, while the proximal parts remain patent as the superior vesical arteries supplying the urinary bladder. These fibrous ligaments are seen on the posterior aspect of the anterior abdominal wall, covered by peritoneum. In contrast, the ligamentum teres is derived from the umbilical vein, and the ligamentum arteriosum arises from the ductus arteriosus.
Guessed Questions (Related to Fetal Circulation and Umbilical Remnants):
2. The remnant of the umbilical vein in adults is known as:
a) Ligamentum arteriosum
b) Ligamentum venosum
c) Ligamentum teres hepatis
d) Medial umbilical ligament
Answer: c) Ligamentum teres hepatis
Explanation: The umbilical vein becomes the ligamentum teres hepatis after birth. It lies in the free margin of the falciform ligament of the liver and connects to the left branch of the portal vein.
3. Clinical: In a newborn, failure of closure of the umbilical vein results in:
a) Patent ductus venosus
b) Umbilical hernia
c) Persistent umbilical vein
d) Patent ductus arteriosus
Answer: c) Persistent umbilical vein
Explanation: A persistent umbilical vein can remain open and act as a collateral pathway in portal hypertension. This condition may manifest as caput medusae due to engorged paraumbilical veins.
4. The ductus arteriosus connects which two fetal structures?
a) Right atrium and left atrium
b) Right ventricle and aorta
c) Pulmonary artery and aorta
d) Left atrium and aorta
Answer: c) Pulmonary artery and aorta
Explanation: The ductus arteriosus connects the pulmonary artery to the descending aorta in fetal life, allowing blood to bypass the nonfunctioning lungs. Postnatally, it closes to form the ligamentum arteriosum.
5. Clinical: Failure of ductus arteriosus to close after birth leads to:
a) Coarctation of aorta
b) Patent ductus arteriosus
c) Tetralogy of Fallot
d) Atrial septal defect
Answer: b) Patent ductus arteriosus
Explanation: Patent ductus arteriosus (PDA) occurs when the ductus arteriosus remains open, leading to a left-to-right shunt of blood from the aorta to the pulmonary artery, causing pulmonary hypertension and heart failure if untreated.
6. The proximal part of the umbilical arteries after birth remains patent as:
a) Superior vesical arteries
b) Inferior epigastric arteries
c) Umbilical vein
d) Obturator arteries
Answer: a) Superior vesical arteries
Explanation: The proximal portions of the umbilical arteries persist as the superior vesical arteries, supplying the superior part of the urinary bladder and occasionally the ductus deferens in males.
7. Clinical: The ligamentum arteriosum is located between which structures in adults?
a) Pulmonary artery and aortic arch
b) Pulmonary vein and left atrium
c) Aorta and superior vena cava
d) Right ventricle and pulmonary trunk
Answer: a) Pulmonary artery and aortic arch
Explanation: The ligamentum arteriosum is the fibrous remnant of the ductus arteriosus, connecting the left pulmonary artery to the aortic arch. It is located near the left recurrent laryngeal nerve, which loops around it.
8. Clinical: A newborn with cyanosis that improves with indomethacin likely has:
a) Patent ductus arteriosus
b) Transposition of great vessels
c) Coarctation of aorta
d) Persistent foramen ovale
Answer: a) Patent ductus arteriosus
Explanation: Indomethacin inhibits prostaglandin synthesis, promoting closure of the ductus arteriosus in neonates with PDA. In contrast, prostaglandins maintain ductal patency in conditions like transposition of great vessels.
9. The ligamentum venosum in adults represents the remnant of:
a) Umbilical vein
b) Ductus venosus
c) Umbilical artery
d) Ductus arteriosus
Answer: b) Ductus venosus
Explanation: The ductus venosus, which shunts oxygenated blood from the umbilical vein to the inferior vena cava bypassing the liver, becomes the ligamentum venosum after birth and lies between the left lobe and caudate lobe of the liver.
10. Clinical: A patient with portal hypertension shows distended veins radiating from the umbilicus. These represent:
a) Recanalized umbilical vein
b) Umbilical artery dilation
c) Patent ductus venosus
d) Inferior epigastric varices
Answer: a) Recanalized umbilical vein
Explanation: In portal hypertension, the ligamentum teres (remnant of the umbilical vein) may reopen, forming collateral circulation between the portal and systemic veins, resulting in caput medusae appearance.
11. Clinical: A stab wound near the medial umbilical ligament may injure which underlying structure?
a) Inferior epigastric artery
b) Urinary bladder
c) Superior vesical artery
d) Deep circumflex iliac vein
Answer: c) Superior vesical artery
Explanation: The superior vesical artery lies close to the medial umbilical ligament, which is the remnant of the umbilical artery. Penetrating injuries in this region can damage the bladder or its arterial supply.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Formation of Heart Tube and Cardiac Jelly Composition
Key Definitions:
• Heart tube: The primitive cardiac structure formed by fusion of paired endothelial tubes within the cardiogenic mesoderm, which later differentiates into chambers of the heart.
• Cardiac jelly: The gelatinous connective tissue between the endocardium and myocardium that plays a vital role in cardiac morphogenesis.
• Hyaluronic acid: A glycosaminoglycan secreted mainly by myocardium that provides structural support during heart tube formation.
• Myocardium: The muscular layer of the heart derived from splanchnic mesoderm responsible for contraction and cardiac jelly secretion.
Lead Question (NEET PG 2015):
1. Heart tube is formed in:
a) Hyaluronic acid secreted by endocardium
b) Chondroitin sulfate secreted by endocardium
c) Hyaluronic acid secreted by myocardium
d) Chondroitin sulfate secreted by myocardium
Answer: c) Hyaluronic acid secreted by myocardium
Explanation: The heart tube forms within a gelatinous matrix called cardiac jelly, which lies between the endocardium and myocardium. This jelly primarily contains hyaluronic acid secreted by the myocardium. It plays a crucial role in maintaining the shape of the heart tube, aiding endocardial cushion formation, and guiding cardiac septation. The myocardium (derived from splanchnopleuric mesoderm) secretes this substance early in cardiac morphogenesis. As the heart develops, the cardiac jelly is gradually reduced and replaced by the developing extracellular matrix and myocardial trabeculae.
Guessed Questions (Related to Heart Tube and Cardiac Jelly Formation):
2. The cardiac jelly is located between which two layers of the developing heart?
a) Endocardium and myocardium
b) Myocardium and epicardium
c) Endocardium and pericardium
d) Myocardium and mesocardium
Answer: a) Endocardium and myocardium
Explanation: The cardiac jelly is a thick, acellular matrix located between the endocardial endothelial layer and the muscular myocardium. It supports the developing heart and later contributes to endocardial cushion formation, essential for septation.
3. Clinical: A defect in endocardial cushion development can result in:
a) Atrioventricular septal defect
b) Tetralogy of Fallot
c) Coarctation of aorta
d) Patent ductus arteriosus
Answer: a) Atrioventricular septal defect
Explanation: Endocardial cushions, derived partly from cardiac jelly, contribute to formation of the atrial and ventricular septa and atrioventricular valves. Their abnormal development leads to AV septal defects, commonly seen in Down syndrome.
4. The myocardium is derived from which embryonic layer?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Neural crest
Answer: b) Mesoderm
Explanation: The myocardium originates from the splanchnopleuric layer of lateral plate mesoderm. This mesodermal origin provides contractile cardiac muscle fibers and secretes hyaluronic acid for cardiac jelly formation.
5. Clinical: A baby presents with a single atrioventricular valve and a large central septal defect. The most likely embryologic cause is:
a) Defective endocardial cushion fusion
b) Failure of spiral septum formation
c) Abnormal cardiac looping
d) Improper neural crest migration
Answer: a) Defective endocardial cushion fusion
Explanation: Endocardial cushions contribute to both the atrial and ventricular septa and the formation of AV valves. Failure of their fusion results in complete AV canal defects and single common AV valves.
6. The earliest sign of heart development occurs at which embryonic age?
a) Day 10
b) Day 15
c) Day 18
d) Day 25
Answer: c) Day 18
Explanation: Around day 18, paired endothelial tubes form in the cardiogenic mesoderm. These tubes fuse during the 3rd week to create the primitive heart tube, which begins to beat by day 22–23.
7. Clinical: Excessive persistence of cardiac jelly could interfere with which developmental process?
a) Septation of the heart
b) Formation of cardiac valves
c) Chamber formation
d) All of the above
Answer: d) All of the above
Explanation: Cardiac jelly must be resorbed properly for septation and valve formation. Persistent jelly obstructs the formation of the endocardial cushions, leading to defects like AV septal defects or valve malformations.
8. The heart tube starts to beat at approximately which day of development?
a) Day 15
b) Day 18
c) Day 22
d) Day 28
Answer: c) Day 22
Explanation: Around day 22, the primitive heart tube begins rhythmic contractions, establishing circulation between the embryo and yolk sac. This is the earliest functional activity of any organ system.
9. Clinical: Incomplete resorption of cardiac jelly during development may lead to:
a) Valvular stenosis
b) Aortic arch anomalies
c) Coarctation of the aorta
d) Patent foramen ovale
Answer: a) Valvular stenosis
Explanation: Excessive cardiac jelly can hinder proper valve formation, resulting in thickened or stenotic valves. Normal valve development requires controlled resorption of jelly and remodeling of endocardial cushions.
10. The cardiac jelly primarily consists of:
a) Collagen and elastic fibers
b) Hyaluronic acid and glycoproteins
c) Chondroitin sulfate and fibrin
d) Fibronectin and laminin only
Answer: b) Hyaluronic acid and glycoproteins
Explanation: Cardiac jelly is rich in hyaluronic acid, glycoproteins, and proteoglycans. These substances provide a hydrophilic matrix that maintains the shape of the primitive heart and supports endocardial cushion development.
11. Clinical: If the myocardium fails to secrete sufficient hyaluronic acid, what developmental consequence may occur?
a) Defective endocardial cushion formation
b) Underdeveloped cardiac chambers
c) Impaired looping of the heart tube
d) All of the above
Answer: d) All of the above
Explanation: Hyaluronic acid secreted by the myocardium provides the matrix for heart tube expansion and endocardial cushion formation. Deficiency in its secretion can result in abnormal septation, looping, and underdeveloped cardiac morphology.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Formation of Heart Tube and Early Heart Development
Key Definitions:
• Cardiogenic area: The region of splanchnopleuric mesoderm located cranial to the neural plate where the heart begins to develop.
• Heart tube: A primitive linear structure formed by fusion of paired endocardial tubes during the 3rd week of development.
• Endocardial tube: Paired endothelial channels formed from the splanchnic mesoderm that fuse to form the primitive heart.
• Looping of heart: The process by which the straight heart tube bends and twists to form the future chambers of the heart.
Lead Question (NEET PG 2015):
1. Heart tube is formed at:
a) 3 weeks
b) 6 weeks
c) 10 weeks
d) 12 weeks
Answer: a) 3 weeks
Explanation: The heart tube begins to form at approximately 18–19 days (early in the 3rd week of embryonic life) from paired endocardial tubes in the cardiogenic mesoderm. These tubes fuse to form a single primitive heart tube as the embryo folds. The heart starts beating around day 22–23 and becomes the first functional organ of the embryo. Later, the tube undergoes looping, septation, and chamber formation. By the 8th week, the basic four-chambered structure of the heart is established. Thus, the heart tube appears in the 3rd week of development.
Guessed Questions (Related to Heart Tube Development and Embryonic Circulation):
2. The first organ to start functioning in the embryo is:
a) Brain
b) Heart
c) Liver
d) Kidney
Answer: b) Heart
Explanation: The heart is the first organ to become functional, beginning to beat around day 22–23. This ensures circulation of oxygen and nutrients throughout the developing embryo via the vitelline and umbilical vessels.
3. Clinical: Failure of fusion of the two endocardial heart tubes results in:
a) Cardia bifida
b) Dextrocardia
c) Atrial septal defect
d) Patent foramen ovale
Answer: a) Cardia bifida
Explanation: Cardia bifida is a rare condition in which the paired endocardial tubes fail to fuse, resulting in two separate beating hearts. This occurs due to failure of lateral folding during the 3rd week.
4. The cardiogenic area develops from which germ layer?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Neural crest
Answer: b) Mesoderm
Explanation: The cardiogenic region originates from splanchnopleuric mesoderm, which differentiates into endocardium, myocardium, and epicardium. This mesoderm gives rise to the entire heart and great vessels.
5. Clinical: A newborn with heart on the right side (dextrocardia) most likely has a defect in:
a) Cardiac looping
b) Cardiac septation
c) Chamber formation
d) Endocardial cushion development
Answer: a) Cardiac looping
Explanation: Dextrocardia results from abnormal looping of the heart tube to the left instead of the right. This may occur in isolation or as part of situs inversus, a mirror-image arrangement of organs.
6. The primitive heart tube is derived from which specific region of mesoderm?
a) Paraxial mesoderm
b) Intermediate mesoderm
c) Splanchnopleuric mesoderm
d) Somatopleuric mesoderm
Answer: c) Splanchnopleuric mesoderm
Explanation: The splanchnopleuric mesoderm of the cardiogenic area gives rise to the endothelial tubes that fuse to form the primitive heart. This layer also forms the myocardium and epicardium.
7. Clinical: A fetus with abnormal partitioning of truncus arteriosus will likely develop:
a) Tetralogy of Fallot
b) Patent ductus arteriosus
c) Coarctation of aorta
d) Transposition of great vessels
Answer: a) Tetralogy of Fallot
Explanation: Improper division of the truncus arteriosus by the spiral aorticopulmonary septum leads to Tetralogy of Fallot, which includes ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy.
8. The heart tube begins to beat at approximately:
a) Day 14
b) Day 18
c) Day 22
d) Day 28
Answer: c) Day 22
Explanation: The primitive heart tube begins rhythmic contractions around day 22, establishing the first embryonic circulation. This ensures efficient transport of nutrients and waste products even before placental circulation is fully established.
9. Clinical: A neonate with cyanosis and parallel great vessels likely has a defect in which developmental process?
a) Abnormal aorticopulmonary septum formation
b) Defective endocardial cushion fusion
c) Failure of atrial septation
d) Abnormal truncal ridge migration
Answer: a) Abnormal aorticopulmonary septum formation
Explanation: Transposition of the great vessels occurs due to failure of the aorticopulmonary septum to spiral during development, causing the aorta to arise from the right ventricle and the pulmonary trunk from the left ventricle.
10. The sinus venosus contributes to formation of which cardiac structure?
a) Right atrium (smooth part)
b) Left ventricle
c) Pulmonary trunk
d) Aortic arch
Answer: a) Right atrium (smooth part)
Explanation: The right horn of the sinus venosus becomes incorporated into the wall of the right atrium, forming its smooth posterior portion known as the sinus venarum. This region receives blood from the superior and inferior vena cava.
11. Clinical: An infant with a persistent truncus arteriosus has failure in the development of which embryological structure?
a) Aorticopulmonary septum
b) Bulbus cordis
c) Sinus venosus
d) Endocardial cushions
Answer: a) Aorticopulmonary septum
Explanation: Persistent truncus arteriosus results from failure of the truncal ridges and bulbar ridges to fuse and form the aorticopulmonary septum. This leads to a single arterial trunk supplying both the systemic and pulmonary circulations.
Chapter: Embryology; Topic: Ectodermal Derivatives; Subtopic: Neural Crest Cells – Migration and Derivatives
Key Definitions:
• Neural crest cells: A population of specialized cells derived from the ectoderm at the margins of the neural folds that migrate extensively and differentiate into diverse tissues throughout the body.
• Ectoderm: The outermost germ layer of the embryo, giving rise to the nervous system, epidermis, and various glands.
• Adrenal medulla: The inner region of the adrenal gland derived from neural crest cells, producing catecholamines like epinephrine and norepinephrine.
• Pia and arachnoid mater: Meningeal layers of neural crest origin surrounding the brain and spinal cord.
Lead Question (NEET PG 2015):
1. Structures derived from the neural crest are?
a) Pia
b) Dental papillae
c) Adrenal medulla
d) All of the above
Answer: d) All of the above
Explanation: Neural crest cells arise from the lateral edges of the neural folds during neurulation. They migrate throughout the body and give rise to multiple tissues, including melanocytes, dorsal root ganglia, sympathetic ganglia, Schwann cells, adrenal medulla, pia-arachnoid mater, and connective tissues of the head and neck. The dental papilla, which contributes to dentin formation, also originates from neural crest mesenchyme. Thus, all listed structures — pia, dental papilla, and adrenal medulla — are derived from neural crest cells, illustrating their remarkable multipotency and migratory capacity.
Guessed Questions (Related to Neural Crest Derivatives):
2. Which of the following is not derived from neural crest cells?
a) Melanocytes
b) Schwann cells
c) Anterior pituitary
d) Adrenal medulla
Answer: c) Anterior pituitary
Explanation: The anterior pituitary (adenohypophysis) is derived from ectoderm of Rathke’s pouch, not neural crest cells. The posterior pituitary arises from neuroectoderm. Neural crest cells, however, form melanocytes, Schwann cells, and adrenal medulla.
3. Clinical: A child presents with a tumor of the adrenal medulla. This tumor is derived from neural crest cells and is called:
a) Neuroblastoma
b) Wilms tumor
c) Nephroblastoma
d) Ependymoma
Answer: a) Neuroblastoma
Explanation: Neuroblastoma arises from neural crest-derived cells of the adrenal medulla or sympathetic ganglia. It secretes catecholamines and presents with hypertension, abdominal mass, and elevated urinary VMA levels.
4. The melanocytes of the skin are derived from which embryonic origin?
a) Surface ectoderm
b) Neural crest
c) Mesoderm
d) Endoderm
Answer: b) Neural crest
Explanation: Melanocytes arise from neural crest cells that migrate to the basal layer of the epidermis and produce melanin pigment. Defective migration results in hypopigmented conditions such as piebaldism or Waardenburg syndrome.
5. Clinical: Hirschsprung’s disease results from failure of migration of neural crest cells to form which structure?
a) Enteric ganglia
b) Dorsal root ganglia
c) Adrenal cortex
d) Motor neurons
Answer: a) Enteric ganglia
Explanation: Hirschsprung’s disease (congenital aganglionic megacolon) results from failure of neural crest cells to populate the wall of the distal colon, leading to absence of Auerbach’s and Meissner’s plexuses and functional obstruction.
6. Neural crest cells contribute to all of the following except:
a) Parafollicular cells of thyroid
b) Chromaffin cells of adrenal medulla
c) Odontoblasts
d) Hepatocytes
Answer: d) Hepatocytes
Explanation: Hepatocytes are derived from endoderm of the foregut. Neural crest cells give rise to parafollicular cells, chromaffin cells, odontoblasts, and various craniofacial connective tissues.
7. Clinical: A child with congenital absence of ganglion cells in the gut wall is likely to have defective migration of neural crest cells from:
a) Rhombencephalon
b) Telencephalon
c) Diencephalon
d) Mesencephalon
Answer: a) Rhombencephalon
Explanation: Neural crest cells originating from the rhombencephalon migrate caudally to form enteric ganglia. Defective migration results in Hirschsprung’s disease, leading to megacolon and constipation.
8. The meninges derived from neural crest cells are:
a) Dura mater
b) Pia and arachnoid mater
c) Only pia mater
d) All three layers
Answer: b) Pia and arachnoid mater
Explanation: The pia and arachnoid mater (leptomeninges) are derived from neural crest cells, while the dura mater arises from mesoderm. These layers protect the brain and spinal cord and contain cerebrospinal fluid within the subarachnoid space.
9. Neural crest cells contribute to formation of which cardiac structure?
a) Endocardial cushions
b) Aorticopulmonary septum
c) Myocardium
d) Pericardium
Answer: b) Aorticopulmonary septum
Explanation: Neural crest cells migrate into the truncus arteriosus and bulbus cordis to form the aorticopulmonary septum. Abnormal development leads to congenital heart defects such as Tetralogy of Fallot and transposition of great arteries.
10. Clinical: Waardenburg syndrome, characterized by heterochromia iridis, white forelock, and deafness, is caused by abnormal migration of:
a) Mesodermal cells
b) Neural crest cells
c) Endodermal cells
d) Neuroectodermal cells
Answer: b) Neural crest cells
Explanation: Waardenburg syndrome results from defective neural crest cell migration affecting melanocytes, craniofacial mesenchyme, and cochlear ganglion development. The disorder causes pigmentation anomalies and sensorineural deafness.
11. Neural crest derivatives include all except:
a) Schwann cells
b) Odontoblasts
c) Pia mater
d) Anterior horn motor neurons
Answer: d) Anterior horn motor neurons
Explanation: Motor neurons of the anterior horn are derived from neuroectoderm of the neural tube, not neural crest. Neural crest derivatives include Schwann cells, pia mater, odontoblasts, and sympathetic ganglia.
Chapter: Embryology; Topic: Early Embryonic Development; Subtopic: Notochord – Formation, Function, and Fate
Key Definitions:
• Notochord: A midline rod-like structure formed from mesodermal cells that serves as the primitive axis of the embryo and plays a key inductive role in neural development.
• Primary inductor: The notochord induces overlying ectoderm to form the neural plate, initiating neurulation.
• Hypoblast: The lower layer of the bilaminar embryonic disc, contributing to extraembryonic endoderm but not to the notochord.
• Nucleus pulposus: The central gelatinous core of the intervertebral disc, representing the remnant of the notochord in adults.
Lead Question (NEET PG 2015):
1. True about notochord are all except?
a) Defines axis of embryo
b) Serves as primary inductor
c) Derived from hypoblast
d) Remains as nucleus pulposus
Answer: c) Derived from hypoblast
Explanation: The notochord is derived from mesodermal cells migrating from the primitive node (Hensen’s node), not from the hypoblast. It defines the longitudinal axis of the embryo and induces the formation of the neural plate, marking it as the primary inductor in embryogenesis. Later in development, most of the notochord degenerates, but its remnants persist as the nucleus pulposus of intervertebral discs. The notochord also provides signals for differentiation of surrounding mesoderm into vertebral bodies and contributes to body plan organization.
Guessed Questions (Related to Notochord and Neural Induction):
2. The notochord develops from which embryonic structure?
a) Primitive node
b) Hypoblast
c) Amnion
d) Yolk sac
Answer: a) Primitive node
Explanation: The notochord arises from mesodermal cells migrating cranially from the primitive node. These cells form the notochordal process, which eventually develops into the solid notochordal rod that defines the embryonic midline.
3. Clinical: A congenital defect due to persistence of the notochord is known as:
a) Chordoma
b) Teratoma
c) Meningocele
d) Glioma
Answer: a) Chordoma
Explanation: Chordoma is a rare malignant tumor derived from remnants of the notochord, usually found at the base of the skull or sacrococcygeal region. It is slow-growing and locally invasive, arising from residual notochordal tissue that fails to regress completely.
4. The notochord induces the overlying ectoderm to form:
a) Neural plate
b) Neural crest
c) Somites
d) Myotome
Answer: a) Neural plate
Explanation: The notochord functions as a primary inductor by releasing signaling molecules that induce the overlying ectoderm to thicken and form the neural plate. This marks the beginning of neurulation and the development of the central nervous system.
5. Clinical: If notochordal induction fails, which of the following may result?
a) Neural tube defects
b) Craniofacial abnormalities
c) Hemivertebra
d) All of the above
Answer: d) All of the above
Explanation: Failure of notochordal induction disrupts neural tube formation, leading to neural tube defects such as spina bifida or anencephaly. It may also result in defective vertebral and craniofacial development due to its influence on mesodermal differentiation.
6. The notochord is located between:
a) Neural tube and endoderm
b) Ectoderm and mesoderm
c) Mesoderm and endoderm
d) Ectoderm and yolk sac
Answer: a) Neural tube and endoderm
Explanation: The notochord lies ventral to the neural tube and dorsal to the endoderm. This central position allows it to serve as an organizing center, influencing the development of both neural and mesodermal structures.
7. Clinical: A midline mass at the base of the skull extending into the nasopharynx could represent:
a) Chordoma
b) Meningocele
c) Craniopharyngioma
d) Lipoma
Answer: a) Chordoma
Explanation: Chordomas arise from persistent notochordal remnants and are often located in the clivus or sacrococcygeal region. They may present as midline masses with compressive symptoms in the cranial base or spine.
8. The notochord disappears during development except in which structure?
a) Vertebral body
b) Nucleus pulposus
c) Spinal cord
d) Neural crest
Answer: b) Nucleus pulposus
Explanation: Most of the notochord degenerates as vertebral bodies form, but remnants persist as the nucleus pulposus of intervertebral discs. This gelatinous core maintains flexibility and cushioning between vertebrae.
9. Which germ layer gives rise to the notochord?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) None of the above
Answer: b) Mesoderm
Explanation: The notochord is derived from mesodermal cells that migrate from the primitive node. This axial mesodermal structure is crucial for patterning the surrounding tissues during gastrulation and neurulation.
10. Clinical: A child presents with a dorsal midline sinus discharging mucoid material since birth. This may indicate persistence of:
a) Notochordal canal
b) Neural crest
c) Primitive streak
d) Neurenteric canal
Answer: d) Neurenteric canal
Explanation: Persistence of the neurenteric canal, which transiently connects the amniotic cavity with the yolk sac during notochord formation, may result in midline fistulae or cysts connecting spinal and gastrointestinal structures.
11. The notochordal process communicates transiently with the yolk sac via:
a) Neurenteric canal
b) Allantois
c) Cloacal membrane
d) Amniotic canal
Answer: a) Neurenteric canal
Explanation: During notochordal development, the notochordal process temporarily opens to the yolk sac through the neurenteric canal, maintaining continuity between the amniotic and yolk sac cavities until closure during normal development.
Chapter: Embryology; Topic: Development of Pharyngeal Apparatus; Subtopic: Branchial Cleft Anomalies – Cysts, Sinuses, and Fistulae
Key Definitions:
• Branchial apparatus: A series of arches, pouches, and clefts that appear in the 4th week of embryonic life and contribute to the development of structures in the head and neck.
• Branchial cyst: A congenital epithelial cyst arising from incomplete obliteration of the second branchial cleft, typically located along the anterior border of the sternocleidomastoid muscle.
• Branchial sinus: A blind-ending tract that opens externally on the neck or internally into the pharynx.
• Branchial fistula: A complete tract connecting the skin to the pharynx, resulting from persistence of both branchial cleft and pouch.
Lead Question (NEET PG 2015, March 2013):
1. True about Branchial cyst is:
a) Cysts are more common than sinuses
b) Mostly arises from 2nd branchial system
c) Causes dysphagia and hoarseness
d) Sinus should always be operated
Answer: b) Mostly arises from 2nd branchial system
Explanation: A branchial cyst most commonly arises from remnants of the second branchial cleft or cervical sinus of His. It typically presents as a painless, fluctuant swelling in the upper lateral neck along the anterior border of the sternocleidomastoid. Cysts are less common than sinuses in general branchial anomalies, but among cysts, the second cleft origin predominates. These cysts may become infected or form fistulae. Dysphagia and hoarseness are rare since the lesion does not usually impinge upon deeper structures like the pharynx or larynx.
Guessed Questions (Related to Branchial Apparatus and Anomalies):
2. The second branchial cleft cyst is typically located:
a) Behind the auricle
b) Midline of neck
c) Along anterior border of sternocleidomastoid
d) Below the mandible
Answer: c) Along anterior border of sternocleidomastoid
Explanation: The second branchial cleft cyst lies along the anterior border of the upper third of the sternocleidomastoid muscle. It develops due to persistence of the cervical sinus formed between the 2nd and 4th branchial arches.
3. Clinical: A 12-year-old presents with a painless swelling in the lateral neck that moves neither with deglutition nor with tongue protrusion. The most likely diagnosis is:
a) Thyroglossal cyst
b) Branchial cyst
c) Dermoid cyst
d) Lymphangioma
Answer: b) Branchial cyst
Explanation: A branchial cyst presents as a painless, non-movable lateral neck mass that does not move with swallowing or tongue protrusion, distinguishing it from thyroglossal cysts, which are midline and move with tongue movements.
4. The first branchial cleft gives rise to which structure in normal development?
a) External auditory meatus
b) Middle ear cavity
c) Eustachian tube
d) Mastoid air cells
Answer: a) External auditory meatus
Explanation: The first branchial cleft forms the external auditory meatus, while the first branchial pouch forms the middle ear cavity and Eustachian tube. Persistence of the cleft can result in first branchial cleft anomalies near the ear or parotid gland.
5. Clinical: A patient with recurrent infections and a small opening along the anterior border of the sternocleidomastoid likely has:
a) Branchial sinus
b) Thyroglossal fistula
c) Dermoid sinus
d) Sebaceous cyst
Answer: a) Branchial sinus
Explanation: A branchial sinus is a blind tract opening on the lateral neck, commonly near the anterior border of the sternocleidomastoid, resulting from incomplete closure of the branchial cleft during development.
6. The internal opening of a complete branchial fistula opens into:
a) Tonsillar fossa
b) Pyriform fossa
c) Nasopharynx
d) Posterior pharyngeal wall
Answer: a) Tonsillar fossa
Explanation: A complete branchial fistula results from persistence of both the second branchial cleft and pouch. It extends from the skin externally to the tonsillar fossa internally, passing between the internal and external carotid arteries.
7. Clinical: Infection of a branchial cyst may present as:
a) Tender fluctuant neck swelling
b) Pain radiating to the ear
c) Fever and purulent discharge
d) All of the above
Answer: d) All of the above
Explanation: Secondary infection of a branchial cyst leads to tenderness, fluctuation, and abscess formation. Due to proximity to the glossopharyngeal nerve, pain may radiate to the ear. Surgical excision is the definitive treatment after infection subsides.
8. The branchial apparatus develops during which embryonic week?
a) 2nd week
b) 4th week
c) 6th week
d) 8th week
Answer: b) 4th week
Explanation: The branchial (pharyngeal) apparatus, comprising arches, clefts, and pouches, appears in the 4th week of development. It forms major structures of the head, neck, and face through endodermal, ectodermal, and mesodermal interactions.
9. The second branchial arch gives rise to all of the following except:
a) Stapes
b) Styloid process
c) Mandible
d) Lesser horn of hyoid
Answer: c) Mandible
Explanation: The mandible develops from the first branchial arch (Meckel’s cartilage), whereas the second arch (Reichert’s cartilage) gives rise to the stapes, styloid process, and lesser horn of hyoid.
10. Clinical: A patient presents with a cystic swelling just below the angle of the mandible that becomes inflamed intermittently. The most probable diagnosis is:
a) Branchial cyst
b) Parotid cyst
c) Thyroglossal cyst
d) Dermoid cyst
Answer: a) Branchial cyst
Explanation: A branchial cyst near the angle of the mandible is characteristic of a second branchial cleft remnant. Its typical lateral neck position and intermittent inflammation following upper respiratory infections make it pathognomonic.
11. Clinical: During surgery for a branchial fistula, injury to which nerve is most likely?
a) Hypoglossal nerve
b) Glossopharyngeal nerve
c) Facial nerve
d) Accessory nerve
Answer: b) Glossopharyngeal nerve
Explanation: The tract of a second branchial fistula passes between the internal and external carotid arteries and near the glossopharyngeal nerve. Hence, this nerve is at risk during surgical excision of the fistulous tract.
Chapter: Embryology; Topic: Development of Digestive System; Subtopic: Development of Liver and Associated Structures
Key Definitions:
• Septum transversum: A thick mass of mesoderm between the heart and midgut that contributes to the diaphragm and gives rise to the fibrous stroma of the liver.
• Hepatic diverticulum: A ventral outgrowth from the foregut endoderm that gives rise to hepatocytes and bile ducts.
• Fibrous stroma: The connective tissue framework supporting liver parenchyma, derived from mesodermal cells.
• Foregut endoderm: The embryonic origin of epithelial liver cells, bile ducts, gallbladder, and pancreas.
Lead Question (NEET PG 2015):
1. Fibrous stroma of liver is derived from:
a) Foregut endoderm
b) Midgut endoderm
c) Hindgut endoderm
d) Septum transversum
Answer: d) Septum transversum
Explanation: The fibrous stroma and connective tissue framework of the liver originate from the mesoderm of the septum transversum. The liver parenchyma (hepatocytes) and biliary epithelium develop from endoderm of the foregut, while the stroma, Kupffer cells, and hemopoietic elements arise from mesodermal tissue. The septum transversum also contributes to the central tendon of the diaphragm, which later separates the thoracic and abdominal cavities. Thus, the liver has a dual origin — endodermal (epithelial) and mesodermal (supporting stroma).
Guessed Questions (Related to Development of Liver and Biliary System):
2. The hepatic cells of the liver are derived from:
a) Foregut endoderm
b) Septum transversum
c) Mesonephric duct
d) Hindgut endoderm
Answer: a) Foregut endoderm
Explanation: The hepatocytes and epithelial lining of bile ducts originate from the endoderm of the hepatic diverticulum, an outgrowth of the foregut. This diverticulum also forms the gallbladder and common bile duct.
3. Clinical: Incomplete closure of the connection between hepatic diverticulum and duodenum may lead to:
a) Biliary atresia
b) Choledochal cyst
c) Extrahepatic biliary fistula
d) Pancreatic duct anomaly
Answer: c) Extrahepatic biliary fistula
Explanation: Failure of proper separation between the hepatic diverticulum and duodenal endoderm during development can lead to abnormal communication, resulting in an extrahepatic biliary fistula.
4. The Kupffer cells of the liver are derived from:
a) Foregut endoderm
b) Septum transversum
c) Mesoderm of septum transversum
d) Yolk sac macrophages
Answer: d) Yolk sac macrophages
Explanation: Kupffer cells are liver macrophages derived from the monocyte lineage originating in the yolk sac mesoderm. They migrate to the liver during early hematopoiesis and remain as fixed macrophages in hepatic sinusoids.
5. Clinical: A newborn with jaundice and clay-colored stools is likely suffering from:
a) Biliary atresia
b) Pancreatitis
c) Duodenal stenosis
d) Hepatic cysts
Answer: a) Biliary atresia
Explanation: Biliary atresia results from failure of canalization of the extrahepatic bile ducts, leading to obstruction of bile flow, cholestasis, and jaundice. Clay-colored stools occur due to lack of bile pigments in the intestine.
6. The gallbladder develops from:
a) Foregut endoderm
b) Hindgut endoderm
c) Mesonephric duct
d) Septum transversum
Answer: a) Foregut endoderm
Explanation: The gallbladder and cystic duct arise from the cystic diverticulum, a part of the hepatic diverticulum from the ventral foregut endoderm. This endodermal origin gives rise to its epithelial lining.
7. Clinical: Accessory hepatic ducts result from:
a) Incomplete regression of biliary buds
b) Duplication of hepatic diverticulum
c) Defective bile canaliculi formation
d) Septum transversum anomalies
Answer: a) Incomplete regression of biliary buds
Explanation: Accessory hepatic ducts occur when additional biliary buds fail to regress during development, leading to extra bile ducts connecting to the gallbladder or common hepatic duct.
8. The liver bud grows into which embryonic structure?
a) Dorsal mesogastrium
b) Ventral mesogastrium
c) Septum transversum
d) Pleuroperitoneal membrane
Answer: c) Septum transversum
Explanation: The liver bud (hepatic diverticulum) grows into the septum transversum, where it differentiates into hepatic cords and bile ducts. The septum transversum provides the mesodermal stroma and the site for hepatic sinusoids.
9. Clinical: A congenital absence of gallbladder is due to failure of development of:
a) Cystic diverticulum
b) Hepatic diverticulum
c) Septum transversum
d) Common bile duct
Answer: a) Cystic diverticulum
Explanation: Agenesis of the gallbladder results from failure of cystic diverticulum formation or its degeneration during early embryonic life. It is usually asymptomatic and discovered incidentally.
10. The hepatic veins develop from:
a) Cardinal veins
b) Vitelline veins
c) Umbilical veins
d) Subcardinal veins
Answer: b) Vitelline veins
Explanation: The hepatic veins and sinusoids develop from the vitelline veins, which drain the yolk sac into the sinus venosus. These veins remodel to form the intrahepatic venous system of the liver.
11. Clinical: In a fetus with diaphragmatic hernia, part of the defect may involve improper development of which structure related to the liver?
a) Septum transversum
b) Pleuropericardial folds
c) Dorsal mesogastrium
d) Vitelline duct
Answer: a) Septum transversum
Explanation: The septum transversum forms the central tendon of the diaphragm. Failure in its complete formation or fusion with other diaphragmatic components can lead to congenital diaphragmatic hernia, sometimes affecting adjacent liver positioning.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Development of Nephrons and Collecting System
Key Definitions:
• Nephron: The functional unit of the kidney, responsible for filtration, reabsorption, and secretion, composed of the glomerulus, tubules, and loop of Henle.
• Metanephros: The definitive kidney formed from the interaction between the ureteric bud and metanephric mesenchyme.
• Ureteric bud: An outgrowth from the mesonephric duct that gives rise to the ureter, renal pelvis, calyces, and collecting ducts.
• Mesonephros: A transient, intermediate kidney structure that functions temporarily during early embryonic life before the metanephros develops.
Lead Question (NEET PG 2015):
1. Nephron is derived from:
a) Ureteric bud
b) Mesonephric duct
c) Metanephros
d) Mesonephros
Answer: c) Metanephros
Explanation: The nephron, the functional unit of the kidney, develops from the metanephric blastema (metanephric mesenchyme), which arises from the intermediate mesoderm. The metanephric mesenchyme interacts with the ureteric bud to form nephrons, including the glomerulus, proximal tubule, loop of Henle, and distal convoluted tubule. The ureteric bud, on the other hand, forms the collecting system (collecting ducts, calyces, renal pelvis, and ureter). This reciprocal induction between the metanephric blastema and ureteric bud ensures proper nephron differentiation and renal development.
Guessed Questions (Related to Development of Urinary System):
2. The ureteric bud gives rise to all of the following except:
a) Collecting ducts
b) Renal pelvis
c) Loop of Henle
d) Ureter
Answer: c) Loop of Henle
Explanation: The loop of Henle develops from the metanephric mesenchyme, not the ureteric bud. The ureteric bud forms the collecting ducts, calyces, renal pelvis, and ureter, representing the collecting system of the kidney.
3. Clinical: A newborn presents with unilateral renal agenesis. The most likely embryological defect is:
a) Failure of metanephric blastema formation
b) Failure of ureteric bud formation
c) Failure of mesonephric duct development
d) Failure of pronephros formation
Answer: b) Failure of ureteric bud formation
Explanation: Unilateral renal agenesis occurs when the ureteric bud fails to develop or fails to contact the metanephric mesenchyme. As a result, nephron induction does not occur, leading to absence of one kidney.
4. The glomerulus and Bowman’s capsule are derived from:
a) Ureteric bud
b) Metanephric mesenchyme
c) Mesonephric duct
d) Cloaca
Answer: b) Metanephric mesenchyme
Explanation: Both the glomerulus and Bowman’s capsule originate from the metanephric mesenchyme, part of the metanephros. These structures form the filtration barrier crucial for renal function.
5. Clinical: Bilateral renal agenesis leads to which fetal condition?
a) Anencephaly
b) Oligohydramnios
c) Polyhydramnios
d) Hydrocephalus
Answer: b) Oligohydramnios
Explanation: Bilateral renal agenesis results in absence of urine formation, leading to oligohydramnios (reduced amniotic fluid). This causes pulmonary hypoplasia, limb deformities, and facial anomalies, collectively known as Potter sequence.
6. The collecting ducts of the kidney develop from:
a) Metanephric mesenchyme
b) Ureteric bud
c) Mesonephric duct
d) Intermediate mesoderm directly
Answer: b) Ureteric bud
Explanation: The collecting ducts originate from branching of the ureteric bud, which is an outgrowth of the mesonephric duct. This structure ultimately gives rise to the entire collecting system of the kidney.
7. Clinical: A cystic kidney in a newborn is caused by abnormal interaction between:
a) Metanephric blastema and ureteric bud
b) Pronephros and mesonephros
c) Ureter and cloaca
d) Glomerulus and collecting duct
Answer: a) Metanephric blastema and ureteric bud
Explanation: Improper reciprocal induction between the metanephric blastema and ureteric bud leads to polycystic or dysplastic kidneys. This defective signaling results in cystic dilation of renal tubules.
8. The mesonephric duct in males later forms:
a) Vas deferens and epididymis
b) Ureter
c) Prostate gland
d) Urethra
Answer: a) Vas deferens and epididymis
Explanation: The mesonephric (Wolffian) duct develops into male reproductive structures — epididymis, vas deferens, and seminal vesicles. In females, it regresses due to absence of testosterone.
9. Clinical: A child with a duplicated ureter likely had which developmental error?
a) Duplication of ureteric bud
b) Duplicated metanephric blastema
c) Fusion of mesonephric ducts
d) Early closure of cloaca
Answer: a) Duplication of ureteric bud
Explanation: Duplication of the ureteric bud before it contacts the metanephric blastema results in a duplicated ureter. The condition can be asymptomatic or lead to urinary obstruction.
10. The pronephros, mesonephros, and metanephros are derived from which embryonic tissue?
a) Intermediate mesoderm
b) Paraxial mesoderm
c) Lateral plate mesoderm
d) Endoderm
Answer: a) Intermediate mesoderm
Explanation: All three renal systems — pronephros, mesonephros, and metanephros — develop from the intermediate mesoderm. This tissue extends longitudinally along the dorsal body wall and differentiates into structures of the urinary and reproductive systems.
11. Clinical: An infant with Potter sequence most likely has which embryological defect?
a) Bilateral renal agenesis
b) Failure of ureteric bud branching
c) Persistence of pronephros
d) Early closure of cloacal membrane
Answer: a) Bilateral renal agenesis
Explanation: Potter sequence results from severe oligohydramnios due to bilateral renal agenesis. The absence of fetal urine causes pulmonary hypoplasia, limb deformities, and flattened facies — classic features of this syndrome.
Chapter: Embryology; Topic: Cardiovascular System; Subtopic: Development of Interatrial Septum
Key Definitions:
• Fossa ovalis: A depression in the interatrial septum of the adult heart, representing the closed foramen ovale of the fetal heart.
• Foramen ovale: An opening in the fetal interatrial septum that allows blood to pass from the right atrium to the left atrium, bypassing the nonfunctional fetal lungs.
• Septum primum: The first septum to develop in the atrium, forming the floor of the fossa ovalis in adults.
• Septum secundum: A muscular septum that grows to the right of septum primum and forms the foramen ovale margin.
Lead Question (NEET PG 2015):
1. Fossa ovalis is a remnant of:
a) Septum primum
b) Septum secundum
c) Septum spurium
d) AV cushion
Answer: a) Septum primum
Explanation: The fossa ovalis, located in the interatrial septum, is the remnant of the foramen ovale which closes after birth. The foramen ovale is formed between the septum primum and septum secundum in the fetus, allowing right-to-left shunting of oxygenated blood. After birth, when pulmonary circulation begins, increased left atrial pressure closes the foramen ovale functionally, and later anatomically, leaving the fossa ovalis as a depression. The floor of the fossa ovalis represents the septum primum, while the upper ridge (limbus fossa ovalis) corresponds to the septum secundum.
Guessed Questions (Related to Fetal Circulation and Atrial Septum):
2. The foramen ovale in fetal life allows blood to flow from:
a) Left atrium to right atrium
b) Right atrium to left atrium
c) Right ventricle to left atrium
d) Pulmonary artery to aorta
Answer: b) Right atrium to left atrium
Explanation: The foramen ovale shunts oxygenated blood from the right atrium to the left atrium, bypassing the fetal lungs which are nonfunctional before birth. This ensures oxygen-rich blood from the placenta reaches systemic circulation efficiently.
3. Closure of foramen ovale after birth occurs primarily due to:
a) Decrease in right atrial pressure
b) Increase in right atrial pressure
c) Increase in right ventricular pressure
d) Increase in pulmonary resistance
Answer: a) Decrease in right atrial pressure
Explanation: After birth, the first breath expands the lungs, decreasing pulmonary resistance and right atrial pressure while increasing left atrial pressure. This pressure difference forces the septum primum against the septum secundum, closing the foramen ovale.
4. Clinical: A patent foramen ovale may lead to which condition?
a) Left-to-right shunt
b) Right-to-left shunt
c) Cyanosis
d) Both b and c
Answer: d) Both b and c
Explanation: A patent foramen ovale allows right-to-left shunting of blood, especially during conditions increasing right atrial pressure. This can cause deoxygenated blood to enter systemic circulation, leading to cyanosis and paradoxical embolism.
5. The limbus fossa ovalis is derived from:
a) Septum primum
b) Septum secundum
c) AV cushion
d) Sinus venosus
Answer: b) Septum secundum
Explanation: The limbus fossa ovalis, a prominent margin around the fossa ovalis, is derived from the septum secundum. It forms the upper boundary of the fossa and ensures one-way flow of blood during fetal life.
6. Clinical: Failure of the foramen ovale to close after birth results in:
a) Tetralogy of Fallot
b) Patent foramen ovale
c) Transposition of great arteries
d) Aortic stenosis
Answer: b) Patent foramen ovale
Explanation: A patent foramen ovale (PFO) is caused by incomplete fusion of the septum primum and septum secundum. It is present in about 25% of adults and may lead to paradoxical emboli or transient ischemic attacks.
7. The interatrial septum develops from:
a) Septum primum and septum secundum
b) Septum spurium and AV cushion
c) Endocardial cushions only
d) Sinus venosus and truncus arteriosus
Answer: a) Septum primum and septum secundum
Explanation: The interatrial septum forms from two overlapping septa — septum primum (thin, membranous) and septum secundum (thick, muscular). Their interaction forms the foramen ovale, essential for fetal circulation.
8. Clinical: In fetal echocardiography, persistence of blood flow through the foramen ovale after birth indicates:
a) Congenital heart block
b) Patent foramen ovale
c) Pulmonary hypertension
d) Double outlet right ventricle
Answer: b) Patent foramen ovale
Explanation: Persistent flow through the foramen ovale after birth suggests incomplete closure, diagnosed as patent foramen ovale. It can predispose to paradoxical embolism where venous emboli pass into systemic circulation.
9. The septum spurium contributes to formation of which cardiac structure?
a) Right atrium roof
b) Left atrium floor
c) Coronary sinus
d) Fossa ovalis
Answer: a) Right atrium roof
Explanation: The septum spurium forms part of the roof of the right atrium by fusion of the right and left venous valves of the sinus venosus, but does not contribute directly to the interatrial septum.
10. Clinical: A patient with patent foramen ovale experiences a stroke following deep vein thrombosis. This is due to:
a) Pulmonary embolism
b) Paradoxical embolism
c) Coronary thrombosis
d) Cerebral aneurysm
Answer: b) Paradoxical embolism
Explanation: A paradoxical embolism occurs when a thrombus passes from the right to the left atrium via a patent foramen ovale, bypassing the lungs and entering systemic circulation, potentially causing a stroke.
11. The functional closure of the foramen ovale occurs:
a) Immediately after birth
b) After one week
c) After one month
d) During fetal life
Answer: a) Immediately after birth
Explanation: Functional closure of the foramen ovale occurs immediately after birth due to increased left atrial pressure as pulmonary circulation begins. Anatomical fusion of septa occurs later, usually within the first year of life, forming the fossa ovalis.
Chapter: Embryology; Topic: Cell Division; Subtopic: Meiotic Prophase I – Stages and Significance
Key Definitions:
• Meiosis: A specialized form of cell division that reduces the chromosome number by half, producing haploid gametes.
• Prophase I: The first and longest stage of meiosis I, during which homologous chromosomes pair and exchange genetic material through crossing over.
• Synapsis: The pairing of homologous chromosomes during zygotene stage of prophase I.
• Crossing over: Exchange of genetic material between non-sister chromatids of homologous chromosomes during pachytene, leading to genetic variation.
Lead Question (NEET PG 2015):
1. Which is not a stage of prophase?
a) Diakinesis
b) Leptotene
c) Zygotene
d) Arachytene
Answer: d) Arachytene
Explanation: Prophase I of meiosis is divided into five distinct stages — leptotene, zygotene, pachytene, diplotene, and diakinesis. Each stage has unique events: pairing of homologous chromosomes, synapsis, and crossing over occur sequentially. The term “Arachytene” is incorrect and does not exist as a recognized substage of prophase I. During this prolonged phase, the genetic material undergoes condensation, recombination, and preparation for segregation. This stage is crucial for ensuring genetic variability and accurate chromosome segregation during gametogenesis.
Guessed Questions (Related to Meiotic Prophase I and Cell Division):
2. Crossing over occurs during which stage of prophase I?
a) Leptotene
b) Zygotene
c) Pachytene
d) Diplotene
Answer: c) Pachytene
Explanation: Crossing over occurs during pachytene, where homologous chromosomes exchange genetic material between non-sister chromatids at chiasmata. This process contributes to genetic diversity among gametes and is mediated by the enzyme recombinase.
3. Synapsis or pairing of homologous chromosomes occurs during:
a) Leptotene
b) Zygotene
c) Diplotene
d) Metaphase
Answer: b) Zygotene
Explanation: During zygotene, homologous chromosomes begin to pair along their lengths through a protein structure called the synaptonemal complex. This pairing is essential for crossing over in the next stage, pachytene.
4. Clinical: Nondisjunction leading to Down syndrome usually occurs during:
a) Prophase I
b) Metaphase I
c) Anaphase I
d) Telophase I
Answer: c) Anaphase I
Explanation: Nondisjunction, the failure of homologous chromosomes to separate properly, occurs during anaphase I of meiosis. This results in aneuploidy, such as trisomy 21 (Down syndrome), when a gamete with an extra chromosome fuses during fertilization.
5. Diplotene stage of prophase I is characterized by:
a) Disappearance of chiasmata
b) Terminalization of chiasmata
c) Separation of homologous chromosomes except at chiasmata
d) Formation of spindle fibers
Answer: c) Separation of homologous chromosomes except at chiasmata
Explanation: In the diplotene stage, homologous chromosomes begin to separate but remain attached at chiasmata — the sites of crossing over. This stage may be prolonged, especially in oocytes, where it can last until puberty.
6. Clinical: Arrest of oocytes in females occurs at which stage of meiosis?
a) Pachytene
b) Diplotene
c) Diakinesis
d) Anaphase I
Answer: b) Diplotene
Explanation: Primary oocytes in females remain arrested in diplotene stage of prophase I from fetal life until puberty. Meiosis resumes during each menstrual cycle after hormonal stimulation by LH.
7. The disappearance of the nuclear membrane and nucleolus occurs during which substage of prophase I?
a) Pachytene
b) Diplotene
c) Diakinesis
d) Leptotene
Answer: c) Diakinesis
Explanation: Diakinesis is the final stage of prophase I, marked by maximal chromosome condensation and disappearance of the nuclear membrane and nucleolus. The spindle apparatus begins to form, preparing for metaphase I alignment.
8. Clinical: A woman’s oocytes remaining arrested for decades may accumulate DNA damage. This increases risk of:
a) Monosomy
b) Polyploidy
c) Aneuploidy
d) Triploidy
Answer: c) Aneuploidy
Explanation: Oocytes arrested in diplotene for prolonged periods are prone to errors during chromosome segregation when meiosis resumes, leading to aneuploidy (e.g., trisomy 21, 18, 13). This risk increases with maternal age.
9. The synaptonemal complex first appears during:
a) Leptotene
b) Zygotene
c) Pachytene
d) Diakinesis
Answer: b) Zygotene
Explanation: The synaptonemal complex, a tripartite protein structure, forms during zygotene and facilitates homologous chromosome pairing and recombination during pachytene.
10. Clinical: A 40-year-old woman gives birth to a baby with trisomy 21. The error most likely occurred during:
a) Maternal meiosis I
b) Maternal meiosis II
c) Spermatogenesis
d) Zygotic mitosis
Answer: a) Maternal meiosis I
Explanation: In most cases of Down syndrome, nondisjunction occurs during maternal meiosis I due to aging oocytes and improper homologous chromosome separation during prophase I and anaphase I.
11. During which meiotic stage does chromosomal recombination (genetic exchange) take place?
a) Leptotene
b) Zygotene
c) Pachytene
d) Diplotene
Answer: c) Pachytene
Explanation: Chromosomal recombination occurs during pachytene as homologous chromosomes exchange segments of genetic material at chiasmata. This ensures genetic diversity among gametes, a fundamental outcome of meiosis.
Chapter: Embryology; Topic: Skeletal System Development; Subtopic: Ossification of Bones
Key Definitions:
• Ossification: The process by which bone tissue is formed, either by replacement of cartilage (endochondral ossification) or directly from mesenchymal tissue (intramembranous ossification).
• Intramembranous ossification: Bone development directly from mesenchymal tissue, seen in flat bones such as mandible and skull bones.
• Endochondral ossification: Bone formation by replacement of a preformed cartilage model, typical of long bones like femur and tibia.
• Mandible: The first bone to start ossifying in the human embryo, beginning around the 6th week of intrauterine life through intramembranous ossification.
Lead Question (NEET PG 2015):
1. First bone to start ossifying:
a) Femur
b) Tibia
c) Scapula
d) Mandible
Answer: d) Mandible
Explanation: The mandible is the first bone in the human body to start ossifying. It begins ossification around the 6th week of intrauterine life by intramembranous ossification, originating from the mesenchyme around Meckel’s cartilage. Although it starts early, it is not the first bone to completely ossify. The process continues postnatally, with secondary cartilaginous ossification centers appearing later. In contrast, long bones like femur and tibia ossify by endochondral ossification, beginning slightly later. Early ossification of the mandible is vital for jaw and oral cavity development.
Guessed Questions (Related to Ossification and Bone Development):
2. The type of ossification seen in flat bones like the mandible and skull bones is:
a) Endochondral ossification
b) Intramembranous ossification
c) Metaplastic ossification
d) Fibrocartilaginous ossification
Answer: b) Intramembranous ossification
Explanation: Intramembranous ossification occurs directly from mesenchymal tissue without a cartilage precursor. It is typical of flat bones such as the mandible, maxilla, and clavicle. Mesenchymal cells differentiate into osteoblasts, which secrete osteoid that later mineralizes to form bone.
3. The first long bone to start ossifying during fetal development is:
a) Humerus
b) Femur
c) Clavicle
d) Tibia
Answer: c) Clavicle
Explanation: The clavicle is the first long bone to start ossifying (around the 5th–6th week of intrauterine life), though part of it undergoes endochondral ossification. It serves as a transitional bone, having both intramembranous and endochondral ossification centers.
4. Clinical: Defective endochondral ossification results in which condition?
a) Achondroplasia
b) Osteogenesis imperfecta
c) Marfan syndrome
d) Rickets
Answer: a) Achondroplasia
Explanation: Achondroplasia is a genetic disorder caused by FGFR3 mutation, leading to defective endochondral ossification. It results in shortened long bones, normal trunk length, and characteristic dwarfism, as flat bones (formed by intramembranous ossification) remain unaffected.
5. Which cartilage acts as a precursor for mandible development?
a) Reichert’s cartilage
b) Meckel’s cartilage
c) Thyroid cartilage
d) Alar cartilage
Answer: b) Meckel’s cartilage
Explanation: The mandible develops in close association with Meckel’s cartilage derived from the first pharyngeal arch. However, the bone does not form from the cartilage itself; instead, mesenchyme around Meckel’s cartilage undergoes intramembranous ossification.
6. Clinical: In osteogenesis imperfecta, the defect lies in the synthesis of which component?
a) Type I collagen
b) Type II collagen
c) Osteocalcin
d) Elastin
Answer: a) Type I collagen
Explanation: Osteogenesis imperfecta results from a defect in type I collagen synthesis, leading to brittle bones and frequent fractures. Since type I collagen is the primary organic component of bone matrix, its deficiency impairs bone strength and resilience.
7. The secondary ossification center in long bones usually appears:
a) Before birth
b) At birth or after
c) During early fetal life
d) Only after puberty
Answer: b) At birth or after
Explanation: Secondary ossification centers typically appear at or after birth, most commonly in the epiphyses of long bones. This allows for postnatal growth in length via the epiphyseal growth plate until skeletal maturity.
8. Clinical: Premature closure of epiphyseal plates results in:
a) Gigantism
b) Achondroplasia
c) Growth retardation
d) Osteomalacia
Answer: c) Growth retardation
Explanation: Premature closure of epiphyseal growth plates halts longitudinal bone growth, resulting in short stature. It can be caused by hormonal imbalances, trauma, or genetic disorders affecting growth plate cartilage.
9. The clavicle is unique among long bones because:
a) It ossifies by endochondral process only
b) It has no secondary ossification centers
c) It ossifies first and partly by intramembranous ossification
d) It is entirely membranous in origin
Answer: c) It ossifies first and partly by intramembranous ossification
Explanation: The clavicle begins ossification earliest (around 5th–6th week IUL) and has both intramembranous (medial part) and endochondral (lateral end) ossification centers. This makes it unique among long bones.
10. The flat bones of the skull develop primarily by which type of ossification?
a) Endochondral ossification
b) Intramembranous ossification
c) Secondary ossification
d) Cartilaginous fusion
Answer: b) Intramembranous ossification
Explanation: Flat bones of the skull (frontal, parietal, occipital) develop directly from mesenchymal condensation without a cartilage model. This process ensures rapid ossification required for protection of the developing brain.
11. Clinical: Delayed closure of fontanelles in infants may indicate deficiency of:
a) Vitamin C
b) Vitamin D
c) Calcium
d) Vitamin K
Answer: b) Vitamin D
Explanation: Vitamin D deficiency impairs calcium and phosphate metabolism, leading to defective mineralization of bone matrix. In infants, this manifests as rickets with delayed fontanelle closure, widened sutures, and bone deformities.
Chapter: Neuroanatomy; Topic: Brain and Ventricular System; Subtopic: Third Ventricle and Its Embryological Derivation
Key Definitions:
• Ventricular system: A series of interconnected cavities within the brain filled with cerebrospinal fluid (CSF).
• Diencephalon: The part of the forebrain containing the thalamus, hypothalamus, epithalamus, and subthalamus; surrounds the third ventricle.
• Third ventricle: A midline cavity between the two halves of the diencephalon that communicates with the lateral ventricles and cerebral aqueduct.
• Cerebrospinal fluid (CSF): A clear fluid produced by the choroid plexuses that cushions the brain and spinal cord, circulating through the ventricles and subarachnoid space.
Lead Question (NEET PG 2015):
1. Third ventricle is the cavity of -
a) Mesencephalon
b) Rhombencephalon
c) Diencephalon
d) Telencephalon
Answer: c) Diencephalon
Explanation: The third ventricle is the cavity of the diencephalon. It lies in the midline between the two halves of the thalamus and hypothalamus. The lateral walls are formed by the thalami, the floor by the hypothalamus, and the roof by the tela choroidea. The third ventricle communicates with each lateral ventricle through the interventricular foramen (of Monro) and with the fourth ventricle via the cerebral aqueduct. It plays an essential role in CSF circulation and acts as a narrow passage connecting higher and lower brain centers.
Guessed Questions (Related to Brain Ventricles and Embryology):
2. The lateral ventricles are cavities of which part of the brain?
a) Telencephalon
b) Diencephalon
c) Mesencephalon
d) Rhombencephalon
Answer: a) Telencephalon
Explanation: The lateral ventricles are paired cavities within the cerebral hemispheres (telencephalon). They communicate with the third ventricle through the interventricular foramina (of Monro) and contain choroid plexuses that secrete CSF.
3. The fourth ventricle is the cavity of which embryonic structure?
a) Mesencephalon
b) Rhombencephalon
c) Diencephalon
d) Telencephalon
Answer: b) Rhombencephalon
Explanation: The fourth ventricle develops from the rhombencephalon (hindbrain) and lies between the pons and medulla anteriorly and the cerebellum posteriorly. It communicates with the subarachnoid space via the foramina of Luschka and Magendie.
4. The cerebral aqueduct connects which two ventricles?
a) Lateral and third ventricles
b) Third and fourth ventricles
c) Fourth ventricle and central canal
d) Lateral ventricles
Answer: b) Third and fourth ventricles
Explanation: The cerebral aqueduct (aqueduct of Sylvius), located in the midbrain, connects the third ventricle of the diencephalon to the fourth ventricle of the hindbrain, allowing CSF to flow downward.
5. The choroid plexus of the third ventricle is formed by:
a) Pia mater and ependyma
b) Arachnoid mater and dura mater
c) Ependyma only
d) Pia mater only
Answer: a) Pia mater and ependyma
Explanation: The choroid plexus is a vascular structure formed by invagination of pia mater covered by ependymal cells. It secretes CSF into the ventricles, maintaining intracranial pressure and nutrient balance.
6. Obstruction of the cerebral aqueduct results in which condition?
a) Communicating hydrocephalus
b) Non-communicating hydrocephalus
c) Subdural effusion
d) CSF leak
Answer: b) Non-communicating hydrocephalus
Explanation: Obstruction of the cerebral aqueduct prevents CSF drainage from the third to fourth ventricle, leading to enlargement of lateral and third ventricles — a form of non-communicating (obstructive) hydrocephalus.
7. The floor of the third ventricle is formed by:
a) Thalamus
b) Hypothalamus
c) Epithalamus
d) Corpus callosum
Answer: b) Hypothalamus
Explanation: The hypothalamus forms the floor and lower part of the lateral walls of the third ventricle, containing important structures like the optic chiasma, tuber cinereum, and mammillary bodies.
8. A lesion causing blockage of the foramina of Luschka and Magendie would lead to accumulation of CSF in:
a) Third ventricle only
b) Fourth ventricle
c) Subarachnoid space
d) Spinal canal only
Answer: b) Fourth ventricle
Explanation: Blockage of the foramina of Luschka and Magendie prevents CSF outflow from the fourth ventricle into the subarachnoid space, leading to dilation of the fourth ventricle and raised intracranial pressure.
9. Which part of the brain surrounds the lateral walls of the third ventricle?
a) Midbrain
b) Thalamus
c) Pons
d) Cerebellum
Answer: b) Thalamus
Explanation: The thalamus forms the lateral walls of the third ventricle, serving as a major relay station for sensory and motor pathways and enclosing the midline cavity of the diencephalon.
10. The central canal of the spinal cord is a continuation of which ventricular structure?
a) Third ventricle
b) Fourth ventricle
c) Lateral ventricle
d) Cerebral aqueduct
Answer: b) Fourth ventricle
Explanation: The central canal of the spinal cord continues downward from the fourth ventricle and carries CSF through the spinal cord, maintaining communication between the cranial and spinal compartments.
11. In a case of pineal tumor, obstruction of the aqueduct of Sylvius can cause dilation of which ventricle?
a) Fourth ventricle
b) Third and lateral ventricles
c) Only third ventricle
d) Lateral ventricles only
Answer: b) Third and lateral ventricles
Explanation: Pineal tumors compress the cerebral aqueduct, blocking CSF flow from the third to fourth ventricle. This causes accumulation and dilation of the third and both lateral ventricles, leading to obstructive hydrocephalus.
Chapter: Embryology; Topic: Development of Pancreas; Subtopic: Dorsal and Ventral Pancreatic Buds
Keyword Definitions:
Pancreas: A mixed gland derived from the endoderm of the foregut that performs both endocrine and exocrine functions.
Dorsal Pancreatic Bud: The first outgrowth from the duodenum forming the body, tail, and upper part of the head of the pancreas.
Ventral Pancreatic Bud: Develops later and contributes to the inferior head and uncinate process.
Pancreatic Ducts: Channels that drain secretions from the pancreas into the duodenum.
Hepatic Diverticulum: An endodermal outpouching forming the liver, gallbladder, and part of the bile ducts.
Lead Question (2015):
Tail of pancreas develops from –
a) Hepatic diverticulum
b) Dorsal pancreatic duct
c) Ventral pancreatic duct
d) All of the above
Explanation:
The **tail of the pancreas** develops from the **dorsal pancreatic bud**, which originates as an outgrowth from the dorsal wall of the duodenum. It forms the body and tail of the pancreas, while the ventral bud gives rise to the uncinate process and inferior head. The hepatic diverticulum is unrelated. Answer: b) Dorsal pancreatic duct.
1)
Which embryological structure gives rise to the major part of the pancreas?
a) Ventral pancreatic bud
b) Dorsal pancreatic bud
c) Hepatic diverticulum
d) Common bile duct
Explanation:
The **dorsal pancreatic bud** forms the majority of the pancreas, including the upper part of the head, body, and tail. The ventral bud contributes only to the lower part of the head and uncinate process. The dorsal bud appears first and fuses later during rotation. Answer: b) Dorsal pancreatic bud.
2)
Which of the following parts of the pancreas is derived from the ventral pancreatic bud?
a) Tail
b) Body
c) Uncinate process
d) Neck
Explanation:
The **ventral pancreatic bud** gives rise to the inferior portion of the head and the **uncinate process**. During development, it rotates posteriorly to fuse with the dorsal bud. The dorsal bud contributes to the remainder of the pancreas, including the body and tail. Answer: c) Uncinate process.
3)
Which duct mainly drains the body and tail of the pancreas?
a) Duct of Wirsung
b) Duct of Santorini
c) Bile duct
d) Accessory hepatic duct
Explanation:
The **duct of Santorini** (accessory pancreatic duct) usually drains the dorsal part of the pancreas, including the body and tail, into the minor duodenal papilla. The main duct (Wirsung) drains the ventral part. Variations exist among individuals. Answer: b) Duct of Santorini.
4)
During development, the ventral pancreatic bud rotates around which structure to fuse with the dorsal bud?
a) Common bile duct
b) Portal vein
c) Duodenum
d) Hepatic artery
Explanation:
The **ventral pancreatic bud** rotates dorsally and to the left **around the duodenum**, bringing it into contact with the dorsal bud. This fusion forms the definitive pancreas, with the ducts joining to create the main pancreatic duct. Answer: c) Duodenum.
5)
In normal development, fusion of pancreatic buds results in formation of –
a) Accessory pancreatic duct
b) Main pancreatic duct
c) Hepatic duct
d) Cystic duct
Explanation:
When the **ventral and dorsal buds** fuse, their ducts also join to form the **main pancreatic duct (duct of Wirsung)**. This duct drains the major portion of the pancreas into the major duodenal papilla. Answer: b) Main pancreatic duct.
6) (Clinical)
A newborn presents with bilious vomiting. Imaging shows pancreatic tissue encircling the duodenum. Which developmental abnormality is this?
a) Pancreas divisum
b) Annular pancreas
c) Agenesis of pancreas
d) Pancreatic cyst
Explanation:
**Annular pancreas** occurs when the ventral pancreatic bud splits and encircles the duodenum, constricting it. This can cause duodenal obstruction and bilious vomiting in newborns. It’s often associated with Down syndrome. Surgical correction may be required. Answer: b) Annular pancreas.
7) (Clinical)
A 45-year-old patient with recurrent pancreatitis shows two separate ducts draining into the duodenum. What is the diagnosis?
a) Annular pancreas
b) Pancreas divisum
c) Agenesis of dorsal pancreas
d) Pancreatic carcinoma
Explanation:
**Pancreas divisum** results from failure of fusion between dorsal and ventral pancreatic ducts, leaving two separate drainage channels. The dorsal duct empties into the minor papilla and may cause recurrent pancreatitis due to inadequate drainage. Answer: b) Pancreas divisum.
8) (Clinical)
A patient with dorsal pancreatic agenesis is most likely to have deficiency of which pancreatic part?
a) Head
b) Body and tail
c) Uncinate process
d) Inferior head only
Explanation:
In **agenesis of the dorsal pancreas**, the body and tail are absent because they originate from the dorsal bud. The head and uncinate process derived from the ventral bud remain intact. It may lead to diabetes due to loss of islet cells. Answer: b) Body and tail.
9) (Clinical)
A mass in the tail of the pancreas is most likely to compress which structure?
a) Superior mesenteric artery
b) Portal vein
c) Spleen
d) Inferior vena cava
Explanation:
The **tail of the pancreas** lies in close proximity to the **hilum of the spleen** and runs within the splenorenal ligament. Therefore, a tumor in this region can compress or invade the spleen or splenic vessels. Answer: c) Spleen.
10) (Clinical)
During pancreatic surgery, which vessels are related to the tail of the pancreas?
a) Superior mesenteric vessels
b) Splenic vessels
c) Portal vein
d) Hepatic veins
Explanation:
The **tail of the pancreas** lies in close relation to the **splenic artery and vein**, running along the superior border of the gland. These vessels are at risk during splenectomy or distal pancreatectomy, requiring careful dissection. Answer: b) Splenic vessels.
Topic: Development of Pancreas; Subtopic: Ventral and Dorsal Pancreatic Buds
Keyword Definitions:
Pancreas: A gland with both exocrine and endocrine functions that develops from foregut endoderm.
Ventral Pancreatic Bud: Arises from the ventral aspect of the duodenum and forms part of the pancreas.
Dorsal Pancreatic Bud: Develops first from the dorsal side and gives rise to the major portion of the pancreas.
Uncinate Process: A projection from the head of the pancreas, derived from the ventral bud.
Pancreatic Ducts: Ducts that drain pancreatic secretions into the duodenum.
Lead Question (2015):
Ventral pancreatic duct give rise to?
a) Body
b) Tail
c) Neck
d) Uncinate process
Explanation:
The ventral pancreatic bud develops near the bile duct and rotates dorsally to fuse with the dorsal bud. It gives rise to the **inferior part of the head and the uncinate process of the pancreas**. The dorsal bud forms the superior part of the head, body, and tail. Answer: d) Uncinate process.
1)
Which part of the pancreas develops from the dorsal pancreatic bud?
a) Head
b) Body
c) Uncinate process
d) Inferior part of head
Explanation:
The dorsal pancreatic bud arises first from the duodenum and forms the **superior part of the head, body, and tail of the pancreas**. The ventral bud contributes only to the inferior head and uncinate process. Answer: b) Body.
2)
The main pancreatic duct is derived from which structure?
a) Dorsal bud only
b) Ventral bud only
c) Both dorsal and ventral buds
d) Common bile duct
Explanation:
After rotation and fusion of the pancreatic buds, the ducts from both buds join to form the main pancreatic duct (duct of Wirsung), which opens into the major duodenal papilla. Thus, it is derived from **both the dorsal and ventral pancreatic buds**. Answer: c) Both dorsal and ventral buds.
3)
In annular pancreas, which embryological error occurs?
a) Failure of dorsal bud to form
b) Non-fusion of pancreatic ducts
c) Ventral bud encircles duodenum
d) Overgrowth of dorsal bud
Explanation:
Annular pancreas occurs when the **ventral pancreatic bud splits and encircles the duodenum**, causing constriction. It results from abnormal migration during rotation. The condition may lead to duodenal obstruction or vomiting in newborns. Answer: c) Ventral bud encircles duodenum.
4)
Which artery mainly supplies the head of the pancreas?
a) Splenic artery
b) Superior mesenteric artery
c) Gastroduodenal artery
d) Inferior pancreaticoduodenal artery
Explanation:
The pancreatic head, derived from both buds, is mainly supplied by the **superior and inferior pancreaticoduodenal arteries**. The superior pancreaticoduodenal branch arises from the gastroduodenal artery, making it the principal source. Answer: c) Gastroduodenal artery.
5)
Which part of the pancreas contains the uncinate process?
a) Tail
b) Head
c) Body
d) Neck
Explanation:
The **uncinate process** is a small hook-like projection extending from the **inferior portion of the head** of the pancreas. It lies behind the superior mesenteric vessels and arises from the ventral pancreatic bud. Answer: b) Head.
6) (Clinical)
A newborn presents with bilious vomiting and duodenal obstruction. Imaging shows pancreatic tissue surrounding the duodenum. What is the most likely diagnosis?
a) Annular pancreas
b) Pancreas divisum
c) Pseudocyst
d) Agenesis of dorsal pancreas
Explanation:
This is a classic presentation of **annular pancreas**, where the ventral pancreatic bud abnormally splits and encircles the duodenum, leading to obstruction. It’s often associated with Down syndrome. Surgical bypass is usually required. Answer: a) Annular pancreas.
7) (Clinical)
A patient with recurrent pancreatitis is found to have two separate pancreatic ducts draining into the duodenum. What embryological anomaly is responsible?
a) Annular pancreas
b) Pancreas divisum
c) Duplication of dorsal bud
d) Agenesis of ventral bud
Explanation:
**Pancreas divisum** results from failure of fusion between the dorsal and ventral pancreatic ducts, leading to two ducts draining separately. This causes impaired drainage and recurrent pancreatitis. It’s the most common congenital anomaly of the pancreas. Answer: b) Pancreas divisum.
8) (Clinical)
A 40-year-old man develops a tumor in the uncinate process compressing nearby vessels. Which vessel is most likely affected?
a) Inferior vena cava
b) Splenic vein
c) Superior mesenteric vessels
d) Portal vein
Explanation:
The **uncinate process** lies posterior to the **superior mesenteric vessels**, so a tumor here compresses them first, possibly affecting venous return or intestinal blood supply. The relation helps in radiological localization of lesions. Answer: c) Superior mesenteric vessels.
9) (Clinical)
During pancreatic surgery, the surgeon notes that the ventral bud-derived part lies posterior to major vessels. Which part is this?
a) Tail
b) Neck
c) Uncinate process
d) Body
Explanation:
The **uncinate process**, derived from the ventral bud, lies posterior to the superior mesenteric vessels. Recognizing this relationship is crucial during pancreatic and duodenal surgeries to avoid vascular injury. Answer: c) Uncinate process.
10) (Clinical)
A patient presents with diabetes due to agenesis of dorsal pancreas. Which parts of the pancreas are missing?
a) Head and uncinate process
b) Body and tail
c) Inferior head only
d) Entire pancreas
Explanation:
**Agenesis of dorsal pancreas** leads to absence of the **body and tail**, which are derived from the dorsal bud. These parts contain most islets of Langerhans, leading to diabetes. The head and uncinate process remain intact. Answer: b) Body and tail.
Chapter: Embryology; Topic: Pharyngeal Arches; Subtopic: Muscular Derivatives of Pharyngeal Arches
Keyword Definitions:
Pharyngeal arches: Series of embryonic structures in the head and neck that give rise to muscles, bones, and nerves.
Pharyngeal muscles: Muscles that form the wall of the pharynx and aid in swallowing.
Branchial apparatus: Collective term for pharyngeal arches, clefts, and pouches.
Mesoderm: Embryonic layer giving rise to muscles and connective tissues.
Cartilage derivatives: Skeletal elements formed from arch mesenchyme.
Lead Question – 2014
Pharyngeal muscles are derived from which pharyngeal arch?
a) 1st
b) 2nd
c) 3rd
d) 5th
Explanation:
Pharyngeal muscles mainly develop from the mesoderm of the fourth and sixth pharyngeal arches. The 4th arch gives rise to pharyngeal constrictors, cricothyroid, and levator veli palatini, while the 6th arch forms intrinsic laryngeal muscles. These arches are supplied by branches of the vagus nerve. Correct answer: Fourth arch.
1) Muscles of mastication are derived from which pharyngeal arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: The muscles of mastication originate from the first pharyngeal arch, also called the mandibular arch. These include temporalis, masseter, medial and lateral pterygoids. The mandibular division of the trigeminal nerve (CN V3) supplies them, confirming their first arch origin. Answer: 1st arch.
2) Stylopharyngeus muscle is derived from?
a) 2nd arch
b) 3rd arch
c) 4th arch
d) 6th arch
Explanation: The stylopharyngeus muscle is the only muscle derived from the third pharyngeal arch. It is supplied by the glossopharyngeal nerve (CN IX). It elevates the pharynx during swallowing, showing its embryologic connection to the third arch. Answer: 3rd arch.
3) Which nerve supplies the muscles derived from the 4th arch?
a) Glossopharyngeal
b) Facial
c) Superior laryngeal
d) Recurrent laryngeal
Explanation: The superior laryngeal branch of the vagus nerve innervates muscles from the fourth arch such as cricothyroid, pharyngeal constrictors, and levator veli palatini. This nerve also carries sensory fibers to the laryngeal mucosa above the vocal cords. Answer: Superior laryngeal nerve.
4) Facial expression muscles originate from which arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: Muscles of facial expression are derived from the second pharyngeal (hyoid) arch. These muscles are innervated by the facial nerve (CN VII). Examples include buccinator, orbicularis oris, and frontalis. Answer: 2nd arch.
5) Clinical Case: A patient with facial nerve palsy cannot close his eye. Which pharyngeal arch origin is affected?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: Orbicularis oculi muscle is derived from the second pharyngeal arch and is supplied by the facial nerve (CN VII). Damage leads to loss of eyelid closure and facial asymmetry. Answer: 2nd arch.
6) Clinical Case: Injury to the recurrent laryngeal nerve affects muscles derived from which arch?
a) 4th
b) 6th
c) 3rd
d) 2nd
Explanation: The recurrent laryngeal nerve supplies muscles derived from the sixth pharyngeal arch. These include intrinsic laryngeal muscles responsible for phonation. Injury leads to hoarseness and vocal cord paralysis. Answer: 6th arch.
7) Which pharyngeal arch gives rise to the mylohyoid muscle?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: The mylohyoid muscle originates from the first pharyngeal arch and assists in elevating the floor of the mouth during swallowing. It is supplied by the mylohyoid branch of the inferior alveolar nerve (CN V3). Answer: 1st arch.
8) Clinical Case: A child with congenital absence of pharyngeal constrictor muscles will have swallowing difficulty due to defect in?
a) 1st arch
b) 3rd arch
c) 4th arch
d) 6th arch
Explanation: Pharyngeal constrictors develop from the fourth arch. Their absence leads to dysphagia. These muscles are innervated by the pharyngeal plexus formed by the vagus nerve. Answer: 4th arch.
9) Stylopharyngeus nerve supply confirms its origin from?
a) CN V
b) CN VII
c) CN IX
d) CN X
Explanation: The stylopharyngeus muscle is supplied by the glossopharyngeal nerve (CN IX), indicating its third arch origin. Each arch is associated with a specific cranial nerve reflecting its embryologic source. Answer: CN IX (3rd arch).
10) Clinical Case: A surgeon injures the external laryngeal nerve during thyroid surgery. Which arch derivative is affected?
a) 3rd
b) 4th
c) 5th
d) 6th
Explanation: The external laryngeal nerve (branch of superior laryngeal nerve) innervates cricothyroid, derived from the 4th arch. Injury causes monotonous voice due to inability to tense vocal cords. Answer: 4th arch.
Keyword Definitions:
Pharyngeal arches: Embryonic structures that develop into bones, muscles, and nerves of the head and neck.
Reichert’s cartilage: The cartilaginous core of the second pharyngeal arch giving rise to stapes, styloid process, and part of hyoid bone.
Styloid process: A slender projection from the temporal bone derived from the second arch cartilage.
Facial nerve: Nerve of the second arch supplying muscles of facial expression.
Lead Question - 2014
Styloid process is derived from ?
a) 1st arch
b) 2nd arch
c) 3rd arch
d) 4th arch
Explanation: The styloid process, part of the temporal bone, develops from Reichert’s cartilage of the second pharyngeal arch. Other derivatives of this arch include the stapes, stylohyoid ligament, and lesser horn of hyoid bone. The facial nerve is the nerve of this arch. Hence, the correct answer is 2nd arch.
Guessed Questions:
1) Which nerve is associated with the second pharyngeal arch?
a) Glossopharyngeal nerve
b) Trigeminal nerve
c) Facial nerve
d) Vagus nerve
Explanation: The second pharyngeal arch, also called the hyoid arch, is innervated by the facial nerve (cranial nerve VII). It supplies all muscles derived from this arch, including muscles of facial expression and stapedius. Hence, the correct answer is Facial nerve.
2) Which of the following structures is derived from Reichert’s cartilage?
a) Malleus
b) Incus
c) Stapes
d) Mandible
Explanation: Reichert’s cartilage, the cartilage of the second pharyngeal arch, gives rise to the stapes of the middle ear, styloid process, stylohyoid ligament, and lesser horn of the hyoid. Malleus and incus are derived from the first arch. Hence, the correct answer is Stapes.
3) Which muscle is derived from the second pharyngeal arch?
a) Stylopharyngeus
b) Masseter
c) Orbicularis oculi
d) Cricothyroid
Explanation: The muscles of facial expression, including orbicularis oculi, orbicularis oris, and platysma, develop from the mesoderm of the second pharyngeal arch. These are supplied by the facial nerve. Hence, the correct answer is Orbicularis oculi.
4) The stapes bone develops from which pharyngeal arch?
a) First
b) Second
c) Third
d) Fourth
Explanation: The stapes, one of the auditory ossicles, is derived from Reichert’s cartilage of the second pharyngeal arch. The facial nerve supplies muscles related to this arch, including the stapedius muscle that attaches to the stapes. Hence, the correct answer is Second.
5) The lesser horn of the hyoid bone is derived from?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The lesser horn (cornu) and upper part of the body of the hyoid bone develop from the cartilage of the second pharyngeal arch (Reichert’s cartilage). The greater horn and lower part of the hyoid come from the third arch. Hence, the correct answer is Second arch.
6) A patient with facial nerve palsy is unable to close the eye. This nerve supplies muscles derived from which embryonic arch?
a) First
b) Second
c) Third
d) Fourth
Explanation: The facial nerve (VII) supplies the muscles of facial expression, all derived from the second pharyngeal arch. In facial nerve palsy, loss of orbicularis oculi function prevents eye closure. Hence, the correct answer is Second arch.
7) Which ligament is derived from Reichert’s cartilage?
a) Stylohyoid ligament
b) Sphenomandibular ligament
c) Cricothyroid ligament
d) Stylomandibular ligament
Explanation: The stylohyoid ligament connects the styloid process to the lesser horn of the hyoid bone and is derived from the second pharyngeal arch cartilage. Hence, the correct answer is Stylohyoid ligament.
8) Which structure forms the cartilaginous part of the second pharyngeal arch?
a) Meckel’s cartilage
b) Reichert’s cartilage
c) Thyroid cartilage
d) Arytenoid cartilage
Explanation: Reichert’s cartilage is the cartilaginous component of the second arch, forming the stapes, styloid process, stylohyoid ligament, and lesser horn of hyoid. Hence, the correct answer is Reichert’s cartilage.
9) Which pharyngeal arch contributes to the formation of muscles of facial expression?
a) First
b) Second
c) Third
d) Fourth
Explanation: The second pharyngeal arch forms muscles responsible for facial expression, including orbicularis oris, buccinator, and platysma, all supplied by the facial nerve. Hence, the correct answer is Second.
10) In a congenital anomaly, absence of the styloid process would indicate defective development of which structure?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The styloid process is a derivative of Reichert’s cartilage from the second pharyngeal arch. Its absence suggests defective differentiation of this arch. Hence, the correct answer is Second arch.
Keyword Definitions:
Pharyngeal arches: Embryonic structures that contribute to the development of head and neck components.
First arch (Mandibular arch): Gives rise to maxilla, mandible, malleus, and incus.
Meckel’s cartilage: Cartilaginous bar of the first arch that forms part of the middle ear and mandible.
Derivatives: The structures (bones, muscles, nerves) developed from specific embryological origins.
Lead Question - 2014
Skeletal derivative of Ist arch ?
a) Stapes
b) Hyoid
c) Maxilla
d) Laryngeal cartilages
Explanation: The first pharyngeal arch, also known as the mandibular arch, gives rise to skeletal structures including the maxilla, mandible, malleus, and incus. These are derived from Meckel’s cartilage and mesenchymal condensations around it. Stapes arises from the second arch, and hyoid from second and third arches. Hence, the correct answer is Maxilla.
Guessed Questions:
1) Which nerve supplies muscles derived from the first pharyngeal arch?
a) Facial nerve
b) Trigeminal nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The muscles of mastication, derived from the first pharyngeal arch, are supplied by the mandibular division of the trigeminal nerve (V3). This arch also gives rise to the mylohyoid and tensor tympani muscles. Hence, the correct answer is Trigeminal nerve.
2) Meckel’s cartilage forms which of the following?
a) Stapes
b) Malleus and incus
c) Styloid process
d) Thyroid cartilage
Explanation: Meckel’s cartilage, the cartilaginous component of the first arch, forms the malleus and incus of the middle ear. It also contributes to the sphenomandibular ligament. Other options like stapes or styloid process belong to the second arch. Hence, the correct answer is Malleus and incus.
3) Which artery represents the derivative of the first arch?
a) Maxillary artery
b) Facial artery
c) External carotid artery
d) Lingual artery
Explanation: The artery of the first pharyngeal arch contributes to the formation of the maxillary artery in the adult. The maxillary artery supplies deep structures of the face, derived from the same embryonic arch. Hence, the correct answer is Maxillary artery.
4) Which of the following muscles are derived from the first arch?
a) Stylopharyngeus
b) Muscles of mastication
c) Pharyngeal constrictors
d) Laryngeal muscles
Explanation: Muscles of mastication (masseter, temporalis, medial and lateral pterygoids) are derived from the first arch mesoderm and innervated by mandibular nerve (V3). Stylopharyngeus comes from the third arch. Hence, the correct answer is Muscles of mastication.
5) Which pharyngeal arch anomaly causes mandibulofacial dysostosis?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: Mandibulofacial dysostosis (Treacher-Collins syndrome) results from defective neural crest cell migration into the first pharyngeal arch. This leads to hypoplasia of the zygomatic bone and mandible. Hence, the correct answer is First arch.
6) A child presents with underdeveloped mandible and malformed ears. Which embryological structure is most likely defective?
a) Second pharyngeal arch
b) First pharyngeal arch
c) Third pharyngeal pouch
d) Fourth pharyngeal arch
Explanation: The first pharyngeal arch contributes to formation of the mandible and external ear structures. Defective migration or development leads to micrognathia and ear anomalies. Hence, the correct answer is First pharyngeal arch.
7) The mandibular process forms which adult structure?
a) Lower jaw
b) Upper lip
c) Nasal septum
d) Palatine bone
Explanation: The mandibular process of the first arch fuses in the midline to form the lower jaw (mandible) and lower lip. Hence, the correct answer is Lower jaw.
8) Which of the following is not derived from the first arch?
a) Malleus
b) Maxilla
c) Stapes
d) Mandible
Explanation: The stapes is derived from Reichert’s cartilage of the second pharyngeal arch, whereas the malleus, incus, maxilla, and mandible arise from the first arch. Hence, the correct answer is Stapes.
9) The nerve of the first pharyngeal arch is?
a) Facial nerve
b) Trigeminal nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The first pharyngeal arch is supplied by the mandibular division of the trigeminal nerve (V3), which innervates its muscles and sensory derivatives. Hence, the correct answer is Trigeminal nerve.
10) The anterior belly of digastric muscle is derived from?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation: The anterior belly of the digastric muscle and mylohyoid are derived from the first pharyngeal arch mesoderm and supplied by the mylohyoid branch of mandibular nerve. Hence, the correct answer is First pharyngeal arch.
Chapter: Embryology; Topic: Development of Face and Pharyngeal Arches; Subtopic: Derivatives of the First Pharyngeal Arch
Keyword Definitions:
Pharyngeal Arches: Series of mesodermal outpouchings in the embryonic head region that give rise to various structures in the face, neck, and pharynx.
First Pharyngeal Arch: Also known as the mandibular arch, it contributes to the formation of the maxilla, mandible, malleus, and muscles of mastication.
Maxillary Process: Part of the first arch that forms the upper jaw, lateral part of the upper lip, and part of the palate.
Mandibular Process: Part of the first arch that forms the lower jaw and lower lip.
Frontonasal Process: A separate embryonic prominence that gives rise to the forehead, nose, and philtrum of the upper lip.
Lead Question - 2014
Which of the following is derived from Ist arch?
a) Frontonasal process
b) Maxillary process
c) Mandibular process
d) Both maxillary & mandibular processes
Explanation: The first pharyngeal arch divides into two processes — the maxillary process and the mandibular process. These contribute to the development of the upper and lower jaws, muscles of mastication, and part of the ear ossicles. The frontonasal process is not derived from this arch but from neural crest mesenchyme. Correct answer: Both maxillary & mandibular processes.
1) Which nerve is associated with the first pharyngeal arch?
a) Facial nerve
b) Mandibular nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The nerve of the first pharyngeal arch is the mandibular division of the trigeminal nerve (CN V3). It supplies the muscles derived from this arch, such as the muscles of mastication, mylohyoid, tensor tympani, and tensor veli palatini. Correct answer: Mandibular nerve.
2) Which muscle develops from the first pharyngeal arch?
a) Orbicularis oculi
b) Masseter
c) Stylopharyngeus
d) Cricothyroid
Explanation: The masseter, along with other muscles of mastication (temporalis, medial and lateral pterygoid), develops from the first pharyngeal arch. These muscles are supplied by the mandibular nerve. Other options arise from different arches. Correct answer: Masseter.
3) Which bones are derivatives of Meckel’s cartilage?
a) Malleus and incus
b) Stapes and styloid process
c) Hyoid bone
d) Clavicle
Explanation: The Meckel’s cartilage arises from the first pharyngeal arch and gives rise to the malleus and incus of the middle ear, along with part of the mandible. Stapes and styloid process belong to the second arch. Correct answer: Malleus and incus.
4) A newborn has micrognathia (small jaw) and cleft palate. The most likely developmental defect involves?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation: Defective development of the first pharyngeal arch leads to mandibular and maxillary hypoplasia, resulting in micrognathia and facial deformities as seen in Pierre Robin sequence. Thus, the correct answer is first pharyngeal arch.
5) The anterior two-thirds of the tongue is derived from which arch?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The anterior two-thirds of the tongue develops from the first pharyngeal arch (lateral lingual swellings). Sensory supply is via the mandibular nerve, and taste supply is by the chorda tympani (from second arch). Correct answer: First arch.
6) A child presents with mandibulofacial dysostosis (Treacher Collins syndrome). The defect lies in?
a) Neural crest cells of first arch
b) Mesoderm of second arch
c) Endoderm of third pouch
d) Mesenchyme of fourth arch
Explanation: Treacher Collins syndrome results from defective migration of neural crest cells into the first pharyngeal arch, leading to underdeveloped zygomatic and mandibular structures. Thus, the correct answer is Neural crest cells of first arch.
7) The maxillary prominence contributes to the formation of?
a) Upper lip and cheeks
b) Lower jaw
c) Nose
d) Forehead
Explanation: The maxillary process forms the upper lip (excluding philtrum) and the lateral portions of the face such as the cheeks. It fuses with the medial nasal process to complete the upper lip formation. Correct answer: Upper lip and cheeks.
8) A newborn with cleft lip has failure of fusion between?
a) Maxillary and medial nasal processes
b) Lateral nasal and maxillary processes
c) Mandibular and hyoid arches
d) Frontonasal and mandibular processes
Explanation: A cleft lip results from failure of fusion between the maxillary process and the medial nasal process. This leads to a gap in the upper lip on one or both sides. Correct answer: Maxillary and medial nasal processes.
9) The mandibular process gives rise to?
a) Lower jaw and lower lip
b) Upper jaw and cheeks
c) Nose and philtrum
d) Forehead and scalp
Explanation: The mandibular process, a derivative of the first pharyngeal arch, forms the lower jaw, lower lip, and associated structures. It fuses in the midline to form the mandibular symphysis. Correct answer: Lower jaw and lower lip.
10) A neonate presents with malformed ear ossicles and difficulty in feeding. The likely embryological defect involves?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal pouch
d) Fourth pharyngeal arch
Explanation: The first pharyngeal arch contributes to the formation of malleus and incus, as well as muscles of mastication. Defects in this arch can cause malformation of ear ossicles and feeding problems. Correct answer: First pharyngeal arch.
Chapter: Embryology; Topic: Development of Genital System; Subtopic: Origin of Female Genital Tract
Keyword Definitions:
Vagina: The muscular canal connecting the uterus to the external genitalia, serving as a passage for menstrual flow and childbirth.
Epithelium: A layer of cells forming the surface of the body or lining internal organs and cavities.
Müllerian Duct: Also called paramesonephric duct, it gives rise to female reproductive organs like the uterus, fallopian tubes, and upper vagina.
Urogenital Sinus: An embryonic structure contributing to the lower vagina and urethra.
Mesonephric Duct (Wolffian Duct): A structure primarily involved in the development of male reproductive organs.
Lead Question - 2014
Epithelium of vagina arises from?
a) Ectoderm
b) Wolffian duct
c) Mesoderm
d) Mesonephric duct
Explanation: The upper one-third of the vagina is derived from the Müllerian duct (paramesonephric duct), while the lower two-thirds develop from the urogenital sinus, whose lining is of endodermal origin. The vaginal epithelium, therefore, arises mainly from endoderm (urogenital sinus contribution). The connective tissue and muscle of the vagina are mesodermal in origin. Correct answer: endoderm.
1) Which part of the vagina is derived from the Müllerian duct?
a) Upper one-third
b) Lower two-thirds
c) Entire vagina
d) None
Explanation: The upper one-third of the vagina arises from the Müllerian (paramesonephric) ducts, while the lower two-thirds originate from the urogenital sinus. The junction between these two developmental origins is marked histologically by a transitional zone. Hence, the correct answer is upper one-third derived from Müllerian duct.
2) The lower two-thirds of the vagina develop from?
a) Paramesonephric duct
b) Urogenital sinus
c) Mesonephric duct
d) Cloaca
Explanation: The urogenital sinus (endodermal origin) gives rise to the lower two-thirds of the vagina. It joins the descending Müllerian ducts to form the vaginal plate, which canalizes later to form the vagina. Hence, the correct answer is urogenital sinus.
3) Which embryonic layer gives rise to vaginal epithelium?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neuroectoderm
Explanation: Vaginal epithelium is mainly derived from the endoderm of the urogenital sinus. The mesoderm contributes to the muscular and connective tissue layers, while the Müllerian duct contributes structurally to the upper vagina. Thus, epithelial origin is endodermal. Correct answer: endoderm.
4) In a female newborn with vaginal agenesis, which embryonic structure failed to develop?
a) Müllerian duct
b) Urogenital sinus
c) Cloacal membrane
d) Mesonephric duct
Explanation: Vaginal agenesis occurs when there is defective development of the urogenital sinus or Müllerian ducts. If both fail to fuse or canalize properly, the vagina is absent or rudimentary. Thus, failure of urogenital sinus development leads to lower vaginal agenesis. Correct answer: urogenital sinus.
5) The epithelium of uterus is derived from?
a) Mesoderm
b) Endoderm
c) Ectoderm
d) Neural crest
Explanation: The uterus, fallopian tubes, and upper vagina develop from the paramesonephric (Müllerian) ducts, which are mesodermal in origin. Hence, uterine epithelium arises from mesoderm. This distinguishes it from vaginal epithelium, which arises mainly from endoderm. Correct answer: mesoderm.
6) A 16-year-old girl presents with primary amenorrhea and normal secondary sexual characteristics. Ultrasound shows absence of vagina and uterus. Likely diagnosis?
a) Androgen insensitivity syndrome
b) Müllerian agenesis
c) Turner's syndrome
d) Congenital adrenal hyperplasia
Explanation: In Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome), the Müllerian ducts fail to develop, leading to absence of uterus and upper vagina. Ovaries are normal, hence secondary sexual features are present. Thus, the correct diagnosis is Müllerian agenesis.
7) A female patient with cloacal anomaly shows abnormal connection between vagina and rectum. This defect arises due to failure of?
a) Urorectal septum formation
b) Müllerian duct fusion
c) Cloacal membrane rupture
d) Mesonephric duct regression
Explanation: Cloacal anomalies occur when the urorectal septum fails to divide the cloaca into urogenital and anorectal parts. This leads to abnormal communication between the vagina, urethra, and rectum. Correct answer: urorectal septum formation.
8) The hymen represents the remains of?
a) Cloacal membrane
b) Urogenital sinus
c) Müllerian duct
d) Mesonephric duct
Explanation: The hymen marks the junction between the vagina (from urogenital sinus) and vestibule (from ectoderm). It is a remnant of the cloacal membrane that persists at the vaginal opening. It ruptures during first intercourse or tampon use. Correct answer: cloacal membrane.
9) In a female fetus, the urogenital sinus contributes to which of the following?
a) Lower part of vagina
b) Fallopian tubes
c) Uterus
d) Ovary
Explanation: The urogenital sinus forms the lower two-thirds of the vagina and the vestibule. It does not form the uterus or fallopian tubes, which arise from Müllerian ducts. Hence, the correct answer is lower part of vagina.
10) A newborn girl has a blind vaginal pouch but normal ovaries. The likely cause is?
a) Absence of urogenital sinus contribution
b) Absence of Müllerian duct development
c) Absence of mesonephric duct
d) Defective cloacal membrane
Explanation: A blind vaginal pouch occurs when the Müllerian ducts fail to develop but the urogenital sinus is present. The ovaries (gonadal origin) are unaffected as they arise from the genital ridge. This condition is seen in Müllerian agenesis (MRKH syndrome). Correct answer: absence of Müllerian duct development.
Chapter: Embryology; Topic: Germ Layer Derivatives; Subtopic: Neural Crest Cell Derivatives
Keyword Definitions:
Glomus Cells: Specialized neuroendocrine cells found in carotid and aortic bodies that help regulate blood oxygen levels.
Neural Crest: A transient embryonic structure giving rise to diverse cell types including melanocytes, cranial cartilage, and adrenal medulla cells.
Germ Layers: Three primary layers in embryonic development — ectoderm, mesoderm, and endoderm — from which all tissues originate.
Neuroectoderm: Portion of ectoderm that differentiates into the nervous system and related structures.
Mesoderm: Middle germ layer forming muscles, bones, and blood vessels.
Lead Question - 2014
Glomus cells are derived from?
a) Surface ectoderm
b) Neuroectoderm
c) Mesoderm
d) Endoderm
Explanation: Glomus cells, also called chemoreceptor cells, originate from the neural crest (derived from ectoderm). They are neuroendocrine in nature and are present in the carotid and aortic bodies. These cells sense changes in blood oxygen and carbon dioxide levels and help regulate respiratory activity. Hence, the correct answer is neuroectoderm.
1) Adrenal medulla is derived from?
a) Neural crest
b) Neural tube
c) Mesoderm
d) Endoderm
Explanation: The adrenal medulla arises from neural crest cells, which migrate to the developing adrenal gland and differentiate into chromaffin cells. These cells secrete catecholamines (epinephrine and norepinephrine) that mediate the body’s stress response. The adrenal cortex, however, develops from mesodermal origin. Thus, the answer is neural crest.
2) Parafollicular cells of thyroid develop from?
a) Endoderm
b) Mesoderm
c) Neural crest
d) Surface ectoderm
Explanation: Parafollicular or C cells of the thyroid originate from the neural crest via the ultimobranchial body (a derivative of the 4th pharyngeal pouch). These cells secrete calcitonin, which reduces blood calcium levels by inhibiting bone resorption. The thyroid follicular cells arise from endoderm. Hence, answer: neural crest.
3) Melanocytes of the skin are derived from?
a) Surface ectoderm
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Melanocytes are pigment-producing cells derived from neural crest cells. They migrate into the epidermis, hair follicles, and uveal tract of the eye. Melanocytes synthesize melanin, which protects against ultraviolet radiation. The rest of the epidermis develops from surface ectoderm. Thus, the correct answer is neural crest.
4) Schwann cells originate from?
a) Neural tube
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Schwann cells originate from neural crest cells and are responsible for the myelination of peripheral nerves. They play a vital role in nerve regeneration after injury. Oligodendrocytes, which myelinate the central nervous system, are derived from neuroectoderm. Hence, the correct answer is neural crest.
5) Which of the following structures arises from surface ectoderm?
a) Retina
b) Lens of eye
c) Pituitary gland (posterior lobe)
d) Cerebrum
Explanation: The lens of the eye is derived from surface ectoderm, which invaginates to form the lens vesicle. The retina and posterior pituitary originate from neuroectoderm, and the cerebrum from neural tube. Surface ectoderm also forms epidermis, hair, and nails. Thus, the answer is lens of eye.
6) A 2-year-old child with congenital absence of adrenal medulla likely has a defect in which embryonic structure?
a) Neural crest
b) Neural tube
c) Mesoderm
d) Endoderm
Explanation: Adrenal medulla originates from neural crest cells, which differentiate into chromaffin cells. Defective migration of these cells can result in congenital absence or hypoplasia of adrenal medulla. This causes reduced catecholamine secretion and poor stress response. Thus, the defect is in neural crest origin.
7) A patient with albinism has normal number of melanocytes but lacks melanin. The embryonic origin of affected cells is?
a) Neural crest
b) Surface ectoderm
c) Mesoderm
d) Endoderm
Explanation: In albinism, melanocytes (derived from neural crest) are normal in number but have defective melanin synthesis due to enzyme deficiency (tyrosinase). The pigmentation defect is biochemical, not structural. The embryologic origin of these cells remains neural crest.
8) Tumor of carotid body (chemodectoma) arises from cells derived from?
a) Neural tube
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Chemodectoma or paraganglioma of the carotid body arises from neural crest-derived glomus cells. These cells function as chemoreceptors. Their hyperplasia or neoplasia can result in nonchromaffin paragangliomas, showing neuroendocrine differentiation. Hence, origin is neural crest.
9) A patient with congenital Hirschsprung disease lacks enteric ganglia. This defect is due to abnormal migration of?
a) Neural tube cells
b) Neural crest cells
c) Mesodermal cells
d) Endodermal cells
Explanation: Hirschsprung disease results from failed migration of neural crest cells to the distal gut, leading to absence of enteric ganglion cells in the myenteric and submucosal plexuses. This causes functional obstruction and megacolon. Thus, the embryonic defect involves neural crest cells.
10) Pheochromocytoma arises from which embryonic derivative?
a) Neural tube
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Pheochromocytoma is a tumor of adrenal medulla chromaffin cells derived from the neural crest. These cells secrete catecholamines. The tumor causes episodic hypertension, sweating, and palpitations. Neural crest cells contribute to the sympathetic chain and paraganglia. Hence, the correct answer is neural crest.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Development of Cornea
Keyword Definitions:
Cornea: The transparent anterior portion of the fibrous coat of the eyeball that helps focus light.
Neural crest cells: Migratory embryonic cells contributing to structures like corneal stroma, endothelium, and sclera.
Surface ectoderm: Gives rise to corneal epithelium, lens, and conjunctival lining.
Mesoderm: Embryonic layer forming muscles, blood vessels, and connective tissues in various organs.
Lead Question – 2014
Stroma of cornea develops from?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation:
The corneal stroma develops primarily from neural crest cells that migrate between the surface ectoderm and lens vesicle. These cells produce collagen fibers and keratocytes that maintain corneal transparency. The surface ectoderm forms the corneal epithelium, while the endothelium and stroma originate from neural crest, not mesodermal sources.
1) The corneal epithelium develops from?
a) Neural ectoderm
b) Surface ectoderm
c) Neural crest
d) Mesoderm
The corneal epithelium is derived from the surface ectoderm. It forms a stratified squamous non-keratinized layer that provides protection and transparency. The surface ectoderm also contributes to the formation of the lens and conjunctival epithelium, highlighting its key role in anterior eye development.
2) Corneal endothelium arises from?
a) Surface ectoderm
b) Neural ectoderm
c) Neural crest
d) Mesoderm
The corneal endothelium is derived from neural crest cells that migrate posteriorly to line the inner corneal surface. It maintains corneal transparency by regulating stromal hydration through ion transport. Any dysfunction of this layer, such as in Fuchs dystrophy, results in corneal edema and visual impairment.
3) Which embryological source gives rise to the sclera?
a) Surface ectoderm
b) Neural crest
c) Neural ectoderm
d) Mesoderm
The sclera develops from neural crest-derived mesenchyme surrounding the optic cup. These cells differentiate into dense connective tissue forming the white outer coat of the eyeball. The sclera provides protection and attachment for extraocular muscles, maintaining the structural integrity of the eye.
4) Which of the following is derived from neural ectoderm?
a) Corneal stroma
b) Lens
c) Retina
d) Corneal epithelium
The retina originates from the neural ectoderm of the optic vesicle. It differentiates into two layers — the outer pigmented and inner sensory layer. Neural ectoderm also gives rise to the optic nerve fibers and part of the iris epithelium, but not to corneal tissues.
5) The corneal transparency is maintained by?
a) Presence of keratin
b) Regular arrangement of collagen
c) High vascularity
d) Thick epithelium
Corneal transparency depends on the regular arrangement of collagen fibrils in the stroma and the dehydrating function of endothelial cells. This precise spacing allows uniform light transmission. The avascular nature of the cornea further prevents light scattering, ensuring optical clarity necessary for vision.
6) A newborn presents with opaque cornea and shallow anterior chamber. Which developmental defect is most likely?
a) Neural crest cell migration failure
b) Incomplete lens vesicle separation
c) Mesodermal hypoplasia
d) Surface ectodermal defect
Failure of neural crest cell migration causes congenital anomalies like Axenfeld-Rieger syndrome and Peters anomaly. These lead to corneal opacity, anterior segment dysgenesis, and glaucoma. Proper neural crest migration is essential for forming corneal stroma, endothelium, trabecular meshwork, and anterior chamber structures.
7) Which condition is associated with defective corneal endothelial pump function?
a) Fuchs endothelial dystrophy
b) Keratoconus
c) Retinitis pigmentosa
d) Marfan syndrome
Fuchs endothelial dystrophy results from progressive degeneration of corneal endothelial cells derived from neural crest. The loss of pump function leads to fluid accumulation and corneal edema, causing blurred vision and morning glare. It is common in older females and may require corneal transplantation.
8) Which part of the developing eye is responsible for inducing corneal formation?
a) Optic vesicle
b) Lens vesicle
c) Surface ectoderm
d) Neural crest
The lens vesicle induces differentiation of the overlying surface ectoderm into corneal epithelium and triggers neural crest migration to form the stroma and endothelium. This inductive interaction is crucial in eye morphogenesis, demonstrating the importance of epithelial-mesenchymal signaling in organ development.
9) Which structure separates the cornea from the iris in adults?
a) Corneal stroma
b) Anterior chamber
c) Aqueous humor
d) Vitreous body
The anterior chamber separates the cornea from the iris. It forms by the resorption of mesenchyme between the developing cornea and iris. Aqueous humor circulates in this space, nourishing avascular corneal and lens tissues and maintaining intraocular pressure.
10) In which embryological week does corneal differentiation begin?
a) 4th week
b) 6th week
c) 7th week
d) 9th week
Corneal differentiation begins around the 6th week of intrauterine life when surface ectoderm interacts with the lens vesicle. Neural crest cells migrate to form the stroma and endothelium. By the 7th week, corneal layers are distinct, and transparency develops later through maturation.
Chapter: Embryology; Topic: Development of Gastrointestinal Tract; Subtopic: Development of Duodenum
Keyword Definitions:
Foregut: Gives rise to pharynx, esophagus, stomach, and part of duodenum up to the opening of bile duct.
Midgut: Forms distal duodenum, jejunum, ileum, and part of large intestine.
Duodenum: The first part of the small intestine, divided into four parts.
Embryonic origin: Refers to the germ layer or gut region from which an organ develops.
Lead Question – 2014
2nd part of duodenum is derived from?
a) Foregut
b) Midgut
c) Both foregut & midgut
d) Hindgut
Explanation:
The second part of the duodenum (descending part) develops partly from the terminal foregut and partly from the proximal midgut. The site where the bile and pancreatic ducts open marks the junction between these two regions. Hence, the correct answer is c) Both foregut & midgut. This dual origin is important for blood supply variations and surgical relevance.
1) The junction between foregut and midgut in the duodenum is marked by?
a) Pylorus
b) Ampulla of Vater
c) Ligament of Treitz
d) Duodenojejunal flexure
The foregut–midgut junction lies near the opening of the bile and pancreatic ducts into the second part of the duodenum, known as the Ampulla of Vater. This region receives dual blood supply from both celiac trunk and superior mesenteric artery, reflecting its embryonic dual origin.
2) Which artery supplies the foregut-derived part of duodenum?
a) Superior mesenteric artery
b) Inferior mesenteric artery
c) Celiac trunk
d) Internal iliac artery
The part of duodenum derived from the foregut is supplied by the Celiac trunk via its branch, the superior pancreaticoduodenal artery. This dual supply pattern is essential in surgeries involving pancreatic head and duodenal resection to prevent ischemic injury.
3) Which part of the duodenum is related to the head of pancreas?
a) First
b) Second
c) Third
d) Fourth
The second part (descending part) of the duodenum is closely related to the head of pancreas. The bile and pancreatic ducts open here, forming the hepatopancreatic ampulla. This anatomical relation is vital in understanding obstructive jaundice due to carcinoma of the pancreatic head.
4) During development, the duodenum becomes C-shaped due to?
a) Growth of stomach
b) Rotation of stomach and pancreas
c) Migration of liver
d) Elongation of midgut
The rotation of the stomach and pancreas causes the duodenum to acquire its C-shaped configuration and become retroperitoneal. This process brings the bile and pancreatic ducts into close proximity, establishing the hepatopancreatic junction.
5) The epithelial lining of duodenum develops from?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neural crest
The epithelial lining of the duodenum is derived from endoderm, which also forms the epithelial cells of other parts of the digestive tract. The surrounding smooth muscle and connective tissue arise from splanchnic mesoderm. This combination forms a fully functional intestinal wall.
6) A neonate presents with bilious vomiting soon after birth. The most likely cause is?
a) Hypertrophic pyloric stenosis
b) Duodenal atresia
c) Hirschsprung disease
d) Malrotation
Bilious vomiting in a neonate indicates obstruction below the opening of the bile duct. Duodenal atresia is a congenital condition caused by failure of recanalization of the duodenum. It is associated with polyhydramnios and the “double bubble” sign on X-ray.
7) Which congenital anomaly involves annular pancreas encircling duodenum?
a) Meckel’s diverticulum
b) Annular pancreas
c) Hirschsprung’s disease
d) Malrotation
In Annular pancreas, the ventral pancreatic bud abnormally encircles the duodenum, causing obstruction. It is due to abnormal migration during rotation of the foregut. This leads to vomiting and feeding intolerance in neonates, often requiring surgical correction.
8) The duodenojejunal flexure lies at which vertebral level?
a) L1
b) L2
c) L3
d) L4
The duodenojejunal flexure lies at the left side of the L2 vertebra, supported by the suspensory ligament of Treitz. This structure marks the end of the duodenum and beginning of the jejunum. Its position is clinically important in differentiating upper from lower GI bleeding.
9) Which of the following structures open into the second part of duodenum?
a) Cystic duct
b) Hepatic ducts
c) Common bile duct and pancreatic duct
d) Main pancreatic duct only
The common bile duct and main pancreatic duct unite to form the hepatopancreatic ampulla (of Vater), which opens into the second part of duodenum at the major duodenal papilla. This opening is guarded by the sphincter of Oddi, controlling bile and pancreatic secretions.
10) Which structure marks the embryological boundary between foregut and midgut in the duodenum?
a) Ampulla of Vater
b) Ligament of Treitz
c) Pylorus
d) Ileocecal junction
The Ampulla of Vater marks the junction between foregut and midgut in the duodenum. This site divides the arterial supply between the celiac trunk and superior mesenteric artery. It is a key landmark during endoscopic retrograde cholangiopancreatography (ERCP) procedures.
Chapter: Embryology; Topic: Development of Germ Layers; Subtopic: Notochord and Its Derivatives
Keyword Definitions:
• Notochord: A rod-like midline structure derived from mesoderm that defines the embryo’s axis and induces neural tube formation.
• Nucleus pulposus: The gelatinous central core of the intervertebral disc, a remnant of the embryonic notochord.
• Annulus fibrosus: The outer fibrocartilaginous ring surrounding the nucleus pulposus, derived from sclerotome.
• Intervertebral disc: A cushion between vertebrae formed from notochordal and mesenchymal tissues.
Lead Question – 2014
Remnant of notochord is ?
a) Annulus fibrosus
b) Nucleus pulposus
c) Ligament flavum
d) Intertransverse ligament
Explanation:
The correct answer is (b) Nucleus pulposus. During embryonic development, the notochord serves as the primary axial structure and induces the neural tube. Most of it degenerates as the vertebral column forms, but remnants persist as the nucleus pulposus in the intervertebral discs. The annulus fibrosus originates from the surrounding mesenchymal cells, not the notochord.
1. The notochord develops from which embryonic layer?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Hypoblast
Explanation:
The correct answer is (b) Mesoderm. The notochord forms from mesodermal cells that migrate cranially from the primitive node. It provides structural support and releases molecular signals such as Sonic Hedgehog (SHH), which guides the development of the neural tube, somites, and surrounding tissues, playing a vital role in body axis formation.
2. Which of the following structures is derived from the notochord?
a) Neural tube
b) Nucleus pulposus
c) Annulus fibrosus
d) Vertebral body
Explanation:
The correct answer is (b) Nucleus pulposus. The nucleus pulposus is the only adult derivative of the notochord. It forms the gelatinous center of intervertebral discs, maintaining spinal flexibility and cushioning vertebrae. The rest of the notochord degenerates as vertebral bodies form around it from mesenchymal sclerotome tissue.
3. The notochord acts as a primary inductor for the development of which structure?
a) Neural tube
b) Amnion
c) Somites
d) Gut tube
Explanation:
The correct answer is (a) Neural tube. The notochord induces the overlying ectoderm to form the neural plate, which folds to form the neural tube, the precursor of the central nervous system. It releases morphogens like SHH, which pattern the ventral neural tube and influence somite differentiation.
4. The vertebral bodies develop from which embryonic source?
a) Notochord
b) Paraxial mesoderm
c) Lateral plate mesoderm
d) Neural crest
Explanation:
The correct answer is (b) Paraxial mesoderm. Paraxial mesoderm segments into somites, which form sclerotomes. Sclerotomes give rise to vertebral bodies and ribs, surrounding the degenerating notochord. The notochord itself persists only as the nucleus pulposus, highlighting the interaction between mesodermal derivatives in axial skeleton formation.
5. The primitive streak gives rise to which of the following?
a) Notochord
b) Neural crest
c) Yolk sac
d) Surface ectoderm
Explanation:
The correct answer is (a) Notochord. The primitive streak is the site where epiblast cells migrate inward to form the three germ layers. The cranial extension of the streak, known as the primitive node, forms the notochordal process, which later differentiates into the definitive notochord that defines the body’s longitudinal axis.
6. Clinical: A midline sacrococcygeal tumor arising from notochord remnants is known as?
a) Chordoma
b) Teratoma
c) Lipoma
d) Ependymoma
Explanation:
The correct answer is (a) Chordoma. Chordomas are rare, malignant tumors originating from notochordal remnants, typically found at the skull base or sacrococcygeal region. They grow slowly but are locally aggressive, eroding bone and compressing adjacent structures. Histologically, they contain physaliphorous cells with vacuolated cytoplasm, confirming notochordal origin.
7. Clinical: A defect in notochord formation will primarily affect which system?
a) Nervous system
b) Digestive system
c) Respiratory system
d) Cardiovascular system
Explanation:
The correct answer is (a) Nervous system. Defective notochordal induction leads to improper formation of the neural plate, resulting in neural tube defects such as spina bifida and anencephaly. The notochord provides essential signals guiding neural differentiation and patterning of the developing central nervous system.
8. Clinical: Which congenital anomaly results from persistent notochordal tissue in the vertebral region?
a) Spina bifida
b) Chordoma
c) Hemivertebra
d) Scoliosis
Explanation:
The correct answer is (b) Chordoma. Persistent notochordal tissue in the vertebral axis can give rise to a chordoma. These tumors often develop in the sacral or cranial region, presenting as a destructive lesion causing pain or neurological symptoms. Their embryologic origin from the notochord distinguishes them from other spinal tumors.
9. Clinical: Failure of notochordal signaling to mesoderm leads to which skeletal deformity?
a) Hemivertebra
b) Polydactyly
c) Spina bifida
d) Kyphosis
Explanation:
The correct answer is (a) Hemivertebra. Incomplete notochordal signaling results in asymmetric vertebral body development. A hemivertebra forms when one half of a vertebra fails to develop, leading to congenital scoliosis. Proper notochordal signaling ensures bilateral symmetry in vertebral segmentation and skeletal axis formation.
10. Clinical: A 50-year-old patient presents with a destructive skull base mass derived from notochordal remnants. What is the most likely diagnosis?
a) Osteosarcoma
b) Chordoma
c) Meningioma
d) Schwannoma
Explanation:
The correct answer is (b) Chordoma. Chordoma of the clivus (skull base) arises from embryonic notochordal remnants. It typically causes cranial nerve compression, leading to diplopia or headache. Imaging shows a midline lytic lesion. Despite surgical resection and radiotherapy, recurrence is common due to its slow but invasive growth pattern.
Chapter: Embryology; Topic: Development of Germ Layers; Subtopic: Notochord Formation
Keyword Definitions:
• Notochord: A rod-like structure derived from mesoderm that defines the body’s axial orientation and induces neural tube formation.
• Hypoblast: The lower layer of the bilaminar disc, contributing to the extraembryonic endoderm.
• Induction: The process by which one group of embryonic cells influences the development of another.
• Nucleus pulposus: The central, gelatinous core of the intervertebral disc, derived from notochordal remnants.
Lead Question – 2014
True about notochord are all except?
a) Defines axis of embryo
b) Serves as primary inductor
c) Derived from hypoblast
d) Remains as nucleus pulposus
Explanation:
The correct answer is (c) Derived from hypoblast. The notochord develops from the mesodermal cells of the primitive streak and node, not from the hypoblast. It defines the embryonic axis, acts as a primary inductor in neural development, and later persists as the nucleus pulposus in intervertebral discs. Hypoblast mainly contributes to the yolk sac lining.
1. The notochord is first formed during which week of development?
a) 1st week
b) 2nd week
c) 3rd week
d) 4th week
Explanation:
The correct answer is (c) 3rd week. The notochord forms during the third week from mesodermal cells migrating through the primitive node. It plays a vital role in establishing the midline and inducing the neural plate to form the neural tube. This event marks the beginning of organogenesis in embryonic development.
2. The structure that induces the formation of the neural tube is?
a) Somite
b) Notochord
c) Neural crest
d) Yolk sac
Explanation:
The correct answer is (b) Notochord. The notochord secretes morphogens like SHH (Sonic Hedgehog) that induce the overlying ectoderm to thicken and form the neural plate, which later folds into the neural tube. This process is called neural induction, a fundamental event in central nervous system development.
3. The notochord is derived from which embryonic germ layer?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Hypoblast
Explanation:
The correct answer is (b) Mesoderm. The notochord arises from axial mesoderm formed by the cells migrating cranially through the primitive node. It separates the ectoderm and endoderm along the midline, providing structural support and molecular signals guiding differentiation of surrounding tissues such as somites and neural tube.
4. The remnant of the notochord in adults is known as?
a) Ligamentum flavum
b) Nucleus pulposus
c) Annulus fibrosus
d) Conus medullaris
Explanation:
The correct answer is (b) Nucleus pulposus. The notochord degenerates in most regions but persists as the nucleus pulposus in intervertebral discs. This gelatinous structure provides cushioning between vertebrae, maintaining spinal flexibility. Surrounding mesenchymal tissue forms the annulus fibrosus, the tough outer ring of the disc.
5. The primitive streak gives rise to all the following except?
a) Notochord
b) Endoderm
c) Ectoderm
d) Mesoderm
Explanation:
The correct answer is (c) Ectoderm. The primitive streak forms mesoderm and endoderm as epiblast cells migrate through it. The cells that remain in place become ectoderm. The primitive node at its anterior end produces the notochordal process, which later develops into the notochord.
6. Clinical: A newborn has remnants of the notochord forming a midline mass at the base of the skull. What is the diagnosis?
a) Teratoma
b) Craniopharyngioma
c) Chordoma
d) Meningocele
Explanation:
The correct answer is (c) Chordoma. Chordoma is a malignant tumor arising from notochordal remnants, often at the skull base (clivus) or sacrococcygeal region. It grows slowly but can invade bone and neural tissue. Histologically, it shows physaliphorous cells with vacuolated cytoplasm, confirming notochordal origin.
7. Clinical: A defect in notochordal signaling affects vertebral column formation. Which anomaly results?
a) Scoliosis
b) Spina bifida
c) Hemivertebra
d) Anencephaly
Explanation:
The correct answer is (c) Hemivertebra. Hemivertebra occurs when notochordal signaling fails to properly segment sclerotomes, leading to incomplete vertebral development. This results in lateral curvature of the spine (congenital scoliosis). Proper notochordal function is crucial for symmetrical vertebral body formation and axial alignment.
8. Clinical: A 20-week fetus shows defective neural tube closure due to disrupted SHH pathway. Which embryonic structure is primarily affected?
a) Notochord
b) Somite
c) Yolk sac
d) Amnion
Explanation:
The correct answer is (a) Notochord. Abnormal Sonic Hedgehog (SHH) expression from the notochord impairs neural tube induction, leading to defects like spina bifida or anencephaly. The notochord serves as a key signaling center directing neural and somite patterning during organogenesis.
9. Clinical: Which of the following results if the notochord fails to induce vertebral body formation?
a) Spina bifida
b) Hemivertebra
c) Vertebral agenesis
d) Myelomeningocele
Explanation:
The correct answer is (c) Vertebral agenesis. Failure of notochordal induction during mesodermal segmentation results in vertebral agenesis, where certain vertebral bodies do not develop. This can cause severe spinal deformities and neurological deficits due to loss of structural support and alignment along the vertebral column.
10. Clinical: A midline sacrococcygeal mass containing notochordal tissue remnants is most likely?
a) Sacrococcygeal teratoma
b) Chordoma
c) Lipoma
d) Dermoid cyst
Explanation:
The correct answer is (b) Chordoma. Sacrococcygeal chordomas are rare, slow-growing tumors originating from notochordal remnants. They often present with pain or bowel obstruction. Despite slow growth, they are locally aggressive and may recur after resection, emphasizing the embryologic importance of notochordal regression in normal development.
Chapter: Embryology; Topic: Development of Genital System; Subtopic: Descent of Testis
Keyword Definitions:
• Testicular descent: The process by which the testes move from the posterior abdominal wall to the scrotum during fetal life.
• Inguinal canal: A passage in the anterior abdominal wall through which the testis descends into the scrotum.
• Gubernaculum: A fibromuscular cord guiding testicular descent.
• Processus vaginalis: A peritoneal diverticulum accompanying the testis during descent, forming the tunica vaginalis later.
Lead Question – 2014
Position of testis at 24–28 weeks of intrauterine life?
a) Inguinal canal
b) Lumbar region
c) Superficial inguinal ring
d) Deep inguinal ring
Explanation:
The correct answer is (d) Deep inguinal ring. At 24–28 weeks of gestation, the testis reaches the deep inguinal ring after descending from the posterior abdominal wall. From the 28th to 32nd week, it traverses the inguinal canal and reaches the scrotum by the 9th month. This process is guided by the gubernaculum and influenced by testosterone and intra-abdominal pressure.
1. During which month of gestation does the testis reach the scrotum?
a) 5th month
b) 7th month
c) 8th month
d) 9th month
Explanation:
The correct answer is (d) 9th month. The testis completes its descent into the scrotum by the 9th month of intrauterine life. Descent occurs in two phases: transabdominal (by 3–7 months) and inguinoscrotal (7–9 months). The gubernaculum and genitofemoral nerve–mediated calcitonin gene-related peptide (CGRP) regulate this descent.
2. Which structure forms the pathway for the descent of testis?
a) Inguinal ligament
b) Gubernaculum
c) Cremaster muscle
d) Dartos fascia
Explanation:
The correct answer is (b) Gubernaculum. The gubernaculum anchors the testis to the scrotum and guides its descent through the inguinal canal. Under hormonal control (testosterone and INSL3), it shortens and pulls the testis into position. Abnormal gubernacular development can cause undescended or ectopic testis.
3. What is the fate of processus vaginalis after testicular descent?
a) Forms tunica vaginalis
b) Forms cremaster muscle
c) Forms dartos muscle
d) Obliterates completely
Explanation:
The correct answer is (a) Forms tunica vaginalis. The distal part of the processus vaginalis persists as the tunica vaginalis around the anterior and lateral sides of the testis, while the proximal portion obliterates. If it remains patent, congenital hydrocele or indirect inguinal hernia may result.
4. Which phase of testicular descent is controlled by INSL3 hormone?
a) Inguinoscrotal phase
b) Transabdominal phase
c) Both phases
d) Postnatal phase
Explanation:
The correct answer is (b) Transabdominal phase. INSL3 (Insulin-like 3 hormone) secreted by fetal Leydig cells acts on gubernaculum receptors to mediate the transabdominal phase of testicular descent. The inguinoscrotal phase, in contrast, is primarily androgen- and genitofemoral nerve–dependent.
5. Failure of testicular descent results in which condition?
a) Hydrocele
b) Varicocele
c) Cryptorchidism
d) Orchitis
Explanation:
The correct answer is (c) Cryptorchidism. Cryptorchidism refers to undescended testes that fail to reach the scrotum. It occurs in about 3% of full-term males and 30% of preterm males. Untreated cases may lead to infertility, testicular cancer, and torsion due to elevated temperature in the abdomen.
6. Clinical: A 1-year-old boy presents with empty scrotum and palpable testis in the inguinal canal. Diagnosis?
a) Ectopic testis
b) Retractile testis
c) Undescended testis
d) Anorchia
Explanation:
The correct answer is (c) Undescended testis. Undescended testis (cryptorchidism) is located along the normal descent pathway, usually in the inguinal canal. Early orchiopexy before 1 year of age is advised to prevent infertility, testicular torsion, and malignancy risk in adulthood.
7. Clinical: A 2-year-old male has a painless, transilluminant swelling in the scrotum. What is the diagnosis?
a) Varicocele
b) Hydrocele
c) Hernia
d) Epididymal cyst
Explanation:
The correct answer is (b) Hydrocele. Hydrocele results from persistence of the processus vaginalis allowing peritoneal fluid to collect around the testis. It appears as a smooth, fluctuant, transilluminant scrotal swelling, commonly resolving spontaneously within infancy or treated surgically if persistent.
8. Clinical: A 3-year-old boy has testis located in the perineum. This represents?
a) Ectopic testis
b) Retractile testis
c) Cryptorchidism
d) Hypogonadism
Explanation:
The correct answer is (a) Ectopic testis. An ectopic testis deviates from the normal descent pathway and may be found in the perineum, thigh, or femoral region. The gubernaculum misdirects the testis. Surgical correction is required to prevent infertility and potential malignancy.
9. Clinical: A newborn’s left testis is not found even in the abdomen on ultrasound. Most likely diagnosis?
a) Undescended testis
b) Ectopic testis
c) Anorchia
d) Retractile testis
Explanation:
The correct answer is (c) Anorchia. Anorchia or “vanishing testis syndrome” results from early vascular accident or regression of the testis during fetal life. It presents with empty scrotum and absent testis on imaging. Elevated gonadotropins (FSH, LH) and low testosterone levels confirm the diagnosis.
10. Clinical: A male infant with inguinal hernia is found to have patent processus vaginalis. The embryologic defect involved is?
a) Gubernaculum persistence
b) Failure of processus vaginalis obliteration
c) Absent tunica albuginea
d) Premature testicular descent
Explanation:
The correct answer is (b) Failure of processus vaginalis obliteration. If the proximal part of the processus vaginalis fails to close, abdominal contents may herniate into the inguinal canal, forming an indirect inguinal hernia. This condition often coexists with hydrocele and is corrected surgically to prevent complications.
Chapter: Embryology; Topic: Development of Genital System; Subtopic: Descent of Testis
Keyword Definitions:
• Deep inguinal ring: Opening in the transversalis fascia through which the spermatic cord and testis descend during fetal life.
• Gubernaculum: Fibrous cord that guides testicular descent into the scrotum.
• Processus vaginalis: Peritoneal diverticulum that accompanies testicular descent.
• Cryptorchidism: Condition where one or both testes fail to descend into the scrotum.
Lead Question – 2014
Testis lies at deep inguinal ring upto?
a) 4 months
b) 5 months
c) 7 months
d) 9 months
Explanation:
The correct answer is (c) 7 months. The testis descends from the posterior abdominal wall to the deep inguinal ring by the 7th month of intrauterine life. It passes through the inguinal canal in the 8th month and reaches the scrotum by the 9th month. This descent is guided by the gubernaculum and controlled hormonally by testosterone and INSL3.
1. Which structure guides the descent of the testis?
a) Processus vaginalis
b) Gubernaculum
c) Cremaster muscle
d) Tunica albuginea
Explanation:
The correct answer is (b) Gubernaculum. The gubernaculum is a fibromuscular structure extending from the lower pole of the testis to the scrotum. It shortens and helps in the transabdominal and inguinoscrotal descent of the testis, under the influence of androgens and genitofemoral nerve stimulation.
2. The processus vaginalis later forms which structure in adults?
a) Tunica vaginalis
b) Tunica albuginea
c) Cremasteric fascia
d) Dartos fascia
Explanation:
The correct answer is (a) Tunica vaginalis. The processus vaginalis is a peritoneal diverticulum that descends with the testis. Its distal part remains as tunica vaginalis covering the front and sides of the testis, while the proximal portion normally obliterates. Failure of closure may lead to congenital hernia or hydrocele.
3. Which hormone primarily regulates testicular descent?
a) Testosterone
b) LH
c) FSH
d) Progesterone
Explanation:
The correct answer is (a) Testosterone. Testosterone secreted by fetal Leydig cells promotes gubernacular shortening and migration of the testis into the scrotum. In addition, Insulin-like peptide 3 (INSL3) and genitofemoral nerve-mediated calcitonin gene-related peptide (CGRP) also play critical roles in testicular descent.
4. The inguinoscrotal phase of testicular descent occurs in which month?
a) 5th month
b) 6th month
c) 7th month
d) 8th month
Explanation:
The correct answer is (d) 8th month. The descent of the testis occurs in two phases: transabdominal (by 3–7 months) and inguinoscrotal (by 7–9 months). During the inguinoscrotal phase, the testis passes through the inguinal canal into the scrotum, guided by the gubernaculum and controlled by hormonal and neural factors.
5. Failure of testicular descent is known as?
a) Ectopic testis
b) Cryptorchidism
c) Hydrocele
d) Varicocele
Explanation:
The correct answer is (b) Cryptorchidism. Cryptorchidism is a developmental defect where the testis fails to descend into the scrotum, remaining in the abdomen or inguinal canal. It leads to infertility due to higher intra-abdominal temperature and increased risk of malignancy and hernia formation.
6. Clinical: A 2-year-old boy presents with empty scrotum. Testis is palpable in the inguinal canal. Diagnosis?
a) Ectopic testis
b) Retractile testis
c) Undescended testis
d) Anorchia
Explanation:
The correct answer is (c) Undescended testis. Undescended (cryptorchid) testis is located along the normal path of descent, commonly within the inguinal canal. It may descend spontaneously by one year of age; if not, orchiopexy is indicated to prevent infertility and testicular malignancy later in life.
7. Clinical: A 3-year-old has testis located in the perineum. What is the condition?
a) Ectopic testis
b) Undescended testis
c) Retractile testis
d) Anorchia
Explanation:
The correct answer is (a) Ectopic testis. Ectopic testis deviates from the normal path of descent and may be found in perineal, femoral, or suprapubic regions. The gubernaculum attaches abnormally, misdirecting the testis. Surgical repositioning is necessary to preserve fertility and avoid complications.
8. Clinical: A newborn with right-sided scrotal swelling transilluminates. Diagnosis?
a) Hydrocele
b) Varicocele
c) Hernia
d) Epididymitis
Explanation:
The correct answer is (a) Hydrocele. Hydrocele results from persistence of the processus vaginalis, allowing peritoneal fluid to accumulate around the testis. It presents as a painless, fluctuant, transilluminant swelling in the scrotum, often resolving spontaneously within the first year of life.
9. Clinical: A 20-year-old male has infertility due to failure of testicular descent. What is the most likely histologic change?
a) Leydig cell hyperplasia
b) Seminiferous tubule atrophy
c) Germ cell proliferation
d) Sertoli cell hypertrophy
Explanation:
The correct answer is (b) Seminiferous tubule atrophy. In undescended testes, high temperature impairs spermatogenesis, causing seminiferous tubule atrophy. Leydig cells remain relatively preserved but may undergo hyperplasia. Early surgical correction improves fertility outcomes but does not completely reverse germ cell loss.
10. Clinical: A male infant has absent left testis on examination and ultrasonography. Most probable condition?
a) Retractile testis
b) Anorchia
c) Ectopic testis
d) Torsion of testis
Explanation:
The correct answer is (b) Anorchia. Anorchia refers to congenital absence of one or both testes due to early testicular regression during fetal life. The scrotum appears underdeveloped, and serum testosterone levels are low. Diagnosis is confirmed by ultrasound and hormone assays (low testosterone, high LH/FSH).
Chapter: Embryology; Topic: Development of Gonads; Subtopic: Ovary Development
Keyword Definitions:
• Genital ridge: A thickened area of intermediate mesoderm where gonads develop.
• Sex cords: Cellular cords derived from coelomic epithelium forming gonadal structures.
• Oocytes: Female germ cells derived from primordial germ cells of endodermal origin.
• Follicles: Functional units in the ovary containing developing oocytes surrounded by granulosa cells.
Lead Question – 2014
Not true about development of ovary?
a) Develops in genital ridge
b) Sex cords are derived from coelomic epithelium
c) Oocytes are mesodermal in origin
d) At birth ovary contains 2 million follicles
Explanation:
The correct answer is (c) Oocytes are mesodermal in origin. Oocytes are derived from primordial germ cells, which originate from the yolk sac endoderm and migrate to the genital ridge. The genital ridge arises from intermediate mesoderm, while sex cords arise from coelomic epithelium. At birth, around 2 million follicles remain in each ovary.
1. The medullary cords in ovary develop into?
a) Theca cells
b) Primordial follicles
c) Interstitial cells
d) Corpus luteum
Explanation:
The correct answer is (c) Interstitial cells. Medullary cords in the ovary regress during development, leaving behind interstitial cells derived from the mesenchymal tissue. These cells are hormonally active and play a role in early ovarian steroidogenesis before follicular development begins.
2. Primordial germ cells arise from?
a) Yolk sac endoderm
b) Coelomic epithelium
c) Mesonephros
d) Genital ridge
Explanation:
The correct answer is (a) Yolk sac endoderm. Primordial germ cells originate from the wall of the yolk sac near the allantois and migrate to the developing gonadal ridge. They later differentiate into oogonia in females or spermatogonia in males, determining the gonadal fate.
3. Cortical cords of the ovary develop into?
a) Theca interna
b) Granulosa cells
c) Oogonia
d) Corpus albicans
Explanation:
The correct answer is (b) Granulosa cells. The cortical cords, derived from coelomic epithelium, break into clusters surrounding the oogonia, forming primordial follicles. Granulosa cells support and nourish the developing oocyte and are essential for hormone secretion and follicular maturation.
4. The indifferent gonad appears at which week of gestation?
a) 3rd week
b) 4th week
c) 5th week
d) 6th week
Explanation:
The correct answer is (5th week). The indifferent gonad begins to develop from the intermediate mesoderm during the 5th week. The differentiation into testis or ovary occurs later, guided by genetic and hormonal influences, particularly the presence or absence of the SRY gene on the Y chromosome.
5. In Turner’s syndrome, the gonads develop as?
a) Normal ovaries
b) Streak gonads
c) Dysgenetic testes
d) Ambiguous gonads
Explanation:
The correct answer is (b) Streak gonads. Turner’s syndrome (45,XO) results in underdeveloped gonads known as streak gonads due to absence of one X chromosome. These gonads are nonfunctional fibrous streaks, leading to infertility and lack of secondary sexual characteristics.
6. Clinical: A 20-year-old female with primary amenorrhea and high gonadotropins is diagnosed with streak gonads. What is the chromosomal pattern?
a) 46,XX
b) 45,XO
c) 47,XXX
d) 46,XY
Explanation:
The correct answer is (b) 45,XO. In Turner’s syndrome, streak gonads fail to produce estrogen, leading to elevated FSH and LH levels. The 45,XO karyotype results in short stature, webbed neck, and primary amenorrhea due to absence of ovarian follicular development.
7. Clinical: A newborn female with ambiguous genitalia has 46,XY karyotype. The gonads are undescended. Diagnosis?
a) Androgen insensitivity
b) Gonadal dysgenesis
c) True hermaphroditism
d) Congenital adrenal hyperplasia
Explanation:
The correct answer is (a) Androgen insensitivity. In this disorder, despite 46,XY karyotype, androgen receptors are defective, leading to female external genitalia and undescended testes. The gonads do not differentiate into functional ovaries or testes, a form of testicular feminization.
8. Clinical: A 25-year-old woman with infertility shows multiple small cystic follicles and hyperandrogenism. What is the diagnosis?
a) Turner’s syndrome
b) Polycystic ovary syndrome
c) Premature ovarian failure
d) Mullerian agenesis
Explanation:
The correct answer is (b) Polycystic ovary syndrome. PCOS is caused by hormonal imbalance leading to multiple small cystic follicles, anovulation, and infertility. It is associated with obesity, insulin resistance, and increased LH to FSH ratio, affecting follicular maturation.
9. Clinical: A 15-year-old girl presents with absence of secondary sexual characteristics but normal external genitalia. Likely cause?
a) Gonadal dysgenesis
b) Pituitary tumor
c) Hypothalamic dysfunction
d) Uterine agenesis
Explanation:
The correct answer is (a) Gonadal dysgenesis. In gonadal dysgenesis, ovaries fail to differentiate properly, resulting in lack of estrogen production and secondary sexual development. These individuals present with primary amenorrhea and elevated FSH and LH levels, indicating gonadal failure.
10. Clinical: A 17-year-old female presents with cyclic abdominal pain but no menstruation. On examination, vagina is absent. Diagnosis?
a) Mullerian agenesis
b) Turner’s syndrome
c) Gonadal dysgenesis
d) Imperforate hymen
Explanation:
The correct answer is (a) Mullerian agenesis. In this condition, also called Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, the Müllerian ducts fail to develop, leading to absence of uterus and upper vagina. The ovaries are normal, and secondary sexual characteristics develop normally due to functional gonads.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Origin and Development of Ureteric Bud
Keyword Definitions:
Ureteric Bud: A diverticulum arising from the mesonephric duct that forms the collecting part of the kidney, including the ureter and pelvis.
Mesonephric Duct: Also called Wolffian duct; gives rise to male genital ducts and the ureteric bud.
Metanephros: The permanent kidney formed by interaction between the ureteric bud and metanephric blastema.
Pronephros and Mesonephros: Early embryonic kidney structures that are transient and replaced by the metanephros.
Lead Question - 2014
Ureteric bud arises from?
a) Paramesonephric Duct
b) Mullerian duct
c) Mesonephric duct
d) Mesonephric tubule
Explanation:
The ureteric bud arises as a dorsal outgrowth from the mesonephric (Wolffian) duct near the cloaca around the fifth week of development. It later differentiates into the ureter, renal pelvis, major and minor calyces, and collecting ducts. Therefore, the correct answer is c) Mesonephric duct. This process is vital for kidney formation through interaction with the metanephric blastema.
1. Which embryonic structure induces the formation of the metanephric blastema?
a) Mesonephros
b) Pronephros
c) Ureteric bud
d) Paramesonephric duct
Explanation:
The ureteric bud interacts with the surrounding metanephric mesenchyme (blastema), inducing it to form nephrons. This reciprocal induction process is crucial for kidney development. The correct answer is c) Ureteric bud. Without this signaling, the metanephric blastema fails to differentiate, leading to renal agenesis.
2. Clinical: A newborn with bilateral renal agenesis likely has a defect in which structure?
a) Mesonephric duct
b) Ureteric bud
c) Cloaca
d) Metanephric blastema
Explanation:
Bilateral renal agenesis results from failure of the ureteric bud to develop or interact with the metanephric blastema. The absence of this interaction leads to no kidney formation and severe oligohydramnios (Potter sequence). Thus, the correct answer is b) Ureteric bud.
3. Which of the following structures is derived from the ureteric bud?
a) Nephron
b) Collecting duct
c) Glomerulus
d) Bowman’s capsule
Explanation:
The ureteric bud forms the entire collecting system of the kidney, including the collecting ducts, renal pelvis, calyces, and ureter. Nephrons, glomeruli, and Bowman’s capsules arise from the metanephric blastema. Therefore, the correct answer is b) Collecting duct.
4. Clinical: Duplicated ureter is caused by which developmental abnormality?
a) Early division of the ureteric bud
b) Incomplete regression of mesonephros
c) Absence of metanephros
d) Delayed differentiation of pronephros
Explanation:
Duplication of ureter occurs due to premature branching or duplication of the ureteric bud before it contacts the metanephric blastema. Each branch induces its own collecting system, leading to double ureters or pelves. Hence, the correct answer is a) Early division of the ureteric bud.
5. The mesonephric duct gives rise to all except:
a) Ureteric bud
b) Vas deferens
c) Seminal vesicle
d) Urethra
Explanation:
The mesonephric duct gives rise to the male genital ducts, including the epididymis, vas deferens, and seminal vesicle, and also gives rise to the ureteric bud. However, the urethra develops from the urogenital sinus. Hence, the correct answer is d) Urethra.
6. Clinical: An ectopic ureter opening into the vagina indicates abnormal migration of which structure?
a) Ureteric bud
b) Metanephric blastema
c) Mesonephric duct
d) Paramesonephric duct
Explanation:
An ectopic ureter occurs when the ureteric bud migrates abnormally or connects improperly with the developing urogenital sinus. The condition leads to urinary incontinence in females. Therefore, the correct answer is a) Ureteric bud.
7. Which structure develops from the metanephric blastema?
a) Collecting duct
b) Renal pelvis
c) Nephron tubules
d) Ureter
Explanation:
Metanephric blastema differentiates into nephron tubules including Bowman’s capsule, proximal and distal convoluted tubules, and the loop of Henle. The collecting parts derive from the ureteric bud. Hence, the correct answer is c) Nephron tubules.
8. Clinical: Congenital hydronephrosis is due to obstruction in the outflow tract derived from:
a) Metanephric blastema
b) Ureteric bud
c) Mesonephric duct
d) Pronephros
Explanation:
Hydronephrosis occurs due to obstruction in the ureter, pelvis, or collecting ducts—all derived from the ureteric bud. The backup of urine causes renal dilation and cortical thinning. Therefore, the correct answer is b) Ureteric bud.
9. Which week marks the development of the ureteric bud?
a) 3rd week
b) 4th week
c) 5th week
d) 6th week
Explanation:
The ureteric bud appears as an outgrowth from the mesonephric duct during the fifth week of embryonic development. It extends dorsocranially to meet the metanephric blastema. Hence, the correct answer is c) 5th week.
10. Clinical: Absence of one kidney with a normal contralateral kidney is most likely due to failure of:
a) Mesonephric duct
b) One ureteric bud
c) Metanephric blastema
d) Pronephros
Explanation:
Unilateral renal agenesis results when one ureteric bud fails to form or fails to contact the metanephric blastema. The remaining kidney undergoes compensatory hypertrophy to maintain normal renal function. Thus, the correct answer is b) One ureteric bud.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Origin and Development of Ureteric Bud
Keyword Definitions:
Ureteric Bud: A diverticulum arising from the mesonephric duct that forms the collecting part of the kidney, including the ureter and pelvis.
Mesonephric Duct: Also called Wolffian duct; gives rise to male genital ducts and the ureteric bud.
Metanephros: The permanent kidney formed by interaction between the ureteric bud and metanephric blastema.
Pronephros and Mesonephros: Early embryonic kidney structures that are transient and replaced by the metanephros.
Lead Question - 2014
Ureteric bud arises from?
a) Paramesonephric Duct
b) Mullerian duct
c) Mesonephric duct
d) Mesonephric tubule
Explanation:
The ureteric bud arises as a dorsal outgrowth from the mesonephric (Wolffian) duct near the cloaca around the fifth week of development. It later differentiates into the ureter, renal pelvis, major and minor calyces, and collecting ducts. Therefore, the correct answer is c) Mesonephric duct. This process is vital for kidney formation through interaction with the metanephric blastema.
1. Which embryonic structure induces the formation of the metanephric blastema?
a) Mesonephros
b) Pronephros
c) Ureteric bud
d) Paramesonephric duct
Explanation:
The ureteric bud interacts with the surrounding metanephric mesenchyme (blastema), inducing it to form nephrons. This reciprocal induction process is crucial for kidney development. The correct answer is c) Ureteric bud. Without this signaling, the metanephric blastema fails to differentiate, leading to renal agenesis.
2. Clinical: A newborn with bilateral renal agenesis likely has a defect in which structure?
a) Mesonephric duct
b) Ureteric bud
c) Cloaca
d) Metanephric blastema
Explanation:
Bilateral renal agenesis results from failure of the ureteric bud to develop or interact with the metanephric blastema. The absence of this interaction leads to no kidney formation and severe oligohydramnios (Potter sequence). Thus, the correct answer is b) Ureteric bud.
3. Which of the following structures is derived from the ureteric bud?
a) Nephron
b) Collecting duct
c) Glomerulus
d) Bowman’s capsule
Explanation:
The ureteric bud forms the entire collecting system of the kidney, including the collecting ducts, renal pelvis, calyces, and ureter. Nephrons, glomeruli, and Bowman’s capsules arise from the metanephric blastema. Therefore, the correct answer is b) Collecting duct.
4. Clinical: Duplicated ureter is caused by which developmental abnormality?
a) Early division of the ureteric bud
b) Incomplete regression of mesonephros
c) Absence of metanephros
d) Delayed differentiation of pronephros
Explanation:
Duplication of ureter occurs due to premature branching or duplication of the ureteric bud before it contacts the metanephric blastema. Each branch induces its own collecting system, leading to double ureters or pelves. Hence, the correct answer is a) Early division of the ureteric bud.
5. The mesonephric duct gives rise to all except:
a) Ureteric bud
b) Vas deferens
c) Seminal vesicle
d) Urethra
Explanation:
The mesonephric duct gives rise to the male genital ducts, including the epididymis, vas deferens, and seminal vesicle, and also gives rise to the ureteric bud. However, the urethra develops from the urogenital sinus. Hence, the correct answer is d) Urethra.
6. Clinical: An ectopic ureter opening into the vagina indicates abnormal migration of which structure?
a) Ureteric bud
b) Metanephric blastema
c) Mesonephric duct
d) Paramesonephric duct
Explanation:
An ectopic ureter occurs when the ureteric bud migrates abnormally or connects improperly with the developing urogenital sinus. The condition leads to urinary incontinence in females. Therefore, the correct answer is a) Ureteric bud.
7. Which structure develops from the metanephric blastema?
a) Collecting duct
b) Renal pelvis
c) Nephron tubules
d) Ureter
Explanation:
Metanephric blastema differentiates into nephron tubules including Bowman’s capsule, proximal and distal convoluted tubules, and the loop of Henle. The collecting parts derive from the ureteric bud. Hence, the correct answer is c) Nephron tubules.
8. Clinical: Congenital hydronephrosis is due to obstruction in the outflow tract derived from:
a) Metanephric blastema
b) Ureteric bud
c) Mesonephric duct
d) Pronephros
Explanation:
Hydronephrosis occurs due to obstruction in the ureter, pelvis, or collecting ducts—all derived from the ureteric bud. The backup of urine causes renal dilation and cortical thinning. Therefore, the correct answer is b) Ureteric bud.
9. Which week marks the development of the ureteric bud?
a) 3rd week
b) 4th week
c) 5th week
d) 6th week
Explanation:
The ureteric bud appears as an outgrowth from the mesonephric duct during the fifth week of embryonic development. It extends dorsocranially to meet the metanephric blastema. Hence, the correct answer is c) 5th week.
10. Clinical: Absence of one kidney with a normal contralateral kidney is most likely due to failure of:
a) Mesonephric duct
b) One ureteric bud
c) Metanephric blastema
d) Pronephros
Explanation:
Unilateral renal agenesis results when one ureteric bud fails to form or fails to contact the metanephric blastema. The remaining kidney undergoes compensatory hypertrophy to maintain normal renal function. Thus, the correct answer is b) One ureteric bud.
Chapter: Embryology; Topic: Development of Urogenital System; Subtopic: Development of Kidney
Keyword Definitions:
Ureteric Bud: An outgrowth from the mesonephric duct that forms the collecting system of the kidney.
Metanephros: The permanent kidney that appears in the fifth week of development.
Nephron: The functional filtration unit of the kidney derived from metanephric blastema.
Pronephros and Mesonephros: Primitive kidneys that function temporarily during early embryonic life.
Lead Question - 2014
Excretory system of kidney is derived from?
a) Ureteric bud
b) Mesonephros
c) Metanephros
d) None
Explanation:
The excretory system of the kidney, including nephrons, originates from the metanephric mesoderm (metanephros), while the collecting ducts, calyces, pelvis, and ureter arise from the ureteric bud. Metanephros appears by the 5th week and becomes the permanent kidney. Hence, the correct answer is c) Metanephros.
1. Which part of the kidney develops from the ureteric bud?
a) Glomerulus
b) Collecting ducts
c) Bowman’s capsule
d) Loop of Henle
Explanation:
The ureteric bud gives rise to the collecting ducts, renal pelvis, major and minor calyces, and ureter. The excretory units, including the glomerulus and nephron tubules, come from the metanephric mesenchyme. Therefore, the correct answer is b) Collecting ducts.
2. The metanephric blastema contributes to the formation of:
a) Collecting ducts
b) Nephrons
c) Ureter
d) Pelvis
Explanation:
The metanephric blastema differentiates into nephrons including Bowman’s capsule, proximal tubule, loop of Henle, and distal convoluted tubule. It interacts with the ureteric bud to form the complete kidney structure. Hence, the answer is b) Nephrons.
3. Clinical: A neonate presents with bilateral renal agenesis. Which embryological structure failed to develop?
a) Pronephros
b) Ureteric bud
c) Mesonephros
d) Metanephric blastema
Explanation:
Bilateral renal agenesis occurs due to the failure of the ureteric bud to form or interact with the metanephric blastema. This leads to the absence of both kidneys and causes oligohydramnios (Potter’s sequence). The correct answer is b) Ureteric bud.
4. The ureter develops from:
a) Metanephric blastema
b) Mesonephros
c) Ureteric bud
d) Wolffian duct
Explanation:
The ureter develops as a continuation of the ureteric bud, which sprouts from the Wolffian duct. This bud elongates and differentiates to form the ureter, pelvis, and collecting system of the kidney. Thus, the correct answer is c) Ureteric bud.
5. Clinical: Hydronephrosis in a fetus results mainly due to obstruction in which embryonic derivative?
a) Ureteric bud
b) Metanephros
c) Pronephros
d) Mesonephric duct
Explanation:
Hydronephrosis is caused by obstruction in the ureter or collecting system, which are derivatives of the ureteric bud. Obstruction prevents urine outflow, leading to dilatation of renal pelvis and calyces. Therefore, the correct answer is a) Ureteric bud.
6. Pronephros in humans is:
a) Functional
b) Non-functional
c) Forms nephrons
d) Gives rise to ureter
Explanation:
Pronephros is the first and most primitive form of the kidney in human embryology. It appears early in the 4th week and is non-functional, regressing completely. Hence, the correct answer is b) Non-functional.
7. Clinical: A child with duplicated ureter likely had abnormal branching of which embryonic structure?
a) Mesonephric duct
b) Metanephric blastema
c) Ureteric bud
d) Cloaca
Explanation:
Duplicated ureter occurs due to early division or duplication of the ureteric bud. Each branch may induce separate regions of metanephric tissue, forming two ureters or pelves. Thus, the answer is c) Ureteric bud.
8. Mesonephros contributes to formation of:
a) Testis
b) Kidney
c) Urethra
d) Ovarian follicle
Explanation:
Mesonephros acts as a temporary excretory organ in embryos and contributes to the formation of genital structures such as efferent ducts in males and vestigial remnants in females. Thus, the correct answer is a) Testis.
9. Clinical: Horseshoe kidney results from fusion of the:
a) Ureteric buds
b) Lower poles of metanephric blastema
c) Mesonephric ducts
d) Cloaca
Explanation:
Horseshoe kidney forms when the lower poles of metanephric blastema fuse before ascent. During ascent, the fused kidney gets trapped under the inferior mesenteric artery. The correct answer is b) Lower poles of metanephric blastema.
10. The collecting tubules of kidney arise from:
a) Ureteric bud
b) Metanephric blastema
c) Mesonephros
d) Cloacal membrane
Explanation:
Collecting tubules develop as terminal branches of the ureteric bud. These tubules connect with the distal ends of nephrons derived from the metanephric blastema, allowing urine drainage. Therefore, the correct answer is a) Ureteric bud.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of the Optic Cup
Keyword Definitions:
• Optic Cup: A double-layered structure derived from the optic vesicle, forming retina and related structures.
• Retina: Neural tissue responsible for photoreception and visual transmission.
• Lens: Transparent, biconvex structure focusing light on the retina.
• Cornea: Transparent front part of the eye formed from surface ectoderm and neural crest.
• Sclera: Dense connective tissue forming the outer protective layer of the eyeball, derived from mesoderm and neural crest.
Lead Question - 2014
Optic cup give rise to ?
a) Lens
b) Retina
c) Cornea
d) Sclera
Explanation:
The optic cup, derived from neural ectoderm, gives rise to the retina — both its neural and pigmented layers. The inner layer forms the neural retina, while the outer layer becomes the retinal pigment epithelium. It also contributes to the iris and ciliary body epithelium. Thus, the correct answer is Retina.
1) The outer layer of the optic cup forms?
a) Neural retina
b) Pigmented retina
c) Cornea
d) Lens capsule
Explanation: The optic cup has two layers — the outer layer forms the retinal pigment epithelium, and the inner layer becomes the neural retina. This double-walled cup structure is essential for visual function. Therefore, the correct answer is Pigmented retina.
2) The ciliary body epithelium develops from?
a) Surface ectoderm
b) Neural ectoderm of optic cup
c) Neural crest
d) Mesoderm
Explanation: The epithelium of the ciliary body arises from the anterior extension of both layers of the optic cup, which is of neural ectodermal origin. The connective tissue and muscles of the ciliary body are derived from neural crest cells. Thus, the correct answer is Neural ectoderm of optic cup.
3) Which of the following structures is derived from the inner layer of the optic cup?
a) Retinal pigment epithelium
b) Neural retina
c) Corneal endothelium
d) Lens fibers
Explanation: The inner layer of the optic cup forms the neural retina, which contains photoreceptor cells, bipolar cells, and ganglion cells responsible for vision. Hence, the correct answer is Neural retina.
4) During eye development, lens formation is induced by?
a) Optic vesicle
b) Optic cup
c) Surface ectoderm
d) Neural crest
Explanation: The optic vesicle induces the overlying surface ectoderm to form the lens placode, which invaginates to form the lens vesicle. This inductive interaction is a classic example of epithelial-mesenchymal signaling. Thus, the correct answer is Optic vesicle.
5) A developmental defect in closure of the optic fissure leads to?
a) Aniridia
b) Coloboma
c) Microphthalmia
d) Glaucoma
Explanation: Failure of the embryonic optic fissure to close leads to coloboma, a cleft-like defect usually seen in the iris, choroid, or retina. It may affect one or both eyes. Thus, the correct answer is Coloboma.
6) The iris pigment epithelium develops from?
a) Surface ectoderm
b) Mesoderm
c) Neural ectoderm of optic cup
d) Neural crest
Explanation: The iris pigment epithelium originates from the outer layer of the optic cup, which is neural ectoderm in origin. The connective tissue of the iris is derived from neural crest cells. Hence, the correct answer is Neural ectoderm of optic cup.
7) A neonate presents with a cleft in the inferior iris. The most likely developmental defect is?
a) Failure of optic cup formation
b) Non-closure of choroidal fissure
c) Persistence of hyaloid artery
d) Absent lens placode
Explanation: Non-closure of the choroidal (optic) fissure during embryogenesis causes coloboma, presenting as a notched iris. It results from incomplete fusion of the optic cup margins. Thus, the correct answer is Non-closure of choroidal fissure.
8) Which germ layer gives rise to the corneal epithelium?
a) Surface ectoderm
b) Neural ectoderm
c) Mesoderm
d) Neural crest
Explanation: The corneal epithelium originates from surface ectoderm, while its stroma and endothelium develop from neural crest cells. The cornea is vital for light refraction and transparency. Thus, the correct answer is Surface ectoderm.
9) Failure of lens vesicle separation leads to?
a) Congenital aphakia
b) Persistent lens stalk
c) Microcornea
d) Coloboma
Explanation: Incomplete separation of the lens vesicle from the surface ectoderm causes persistent lens stalk, potentially forming epithelial pearls. It interferes with corneal development. Hence, the correct answer is Persistent lens stalk.
10) Neural crest cells contribute to all except?
a) Sclera
b) Corneal stroma
c) Retina
d) Iris connective tissue
Explanation: Neural crest cells form the sclera, corneal stroma, corneal endothelium, and connective tissue of the iris and ciliary body. The retina, however, is derived from neural ectoderm. Thus, the correct answer is Retina.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of Germ Layers in Eye Formation
Keyword Definitions:
• Optic Cup: A double-walled structure formed from the optic vesicle that gives rise to the retina.
• Neural Ectoderm: Layer of ectoderm giving rise to the brain, spinal cord, retina, and posterior pituitary.
• Surface Ectoderm: Gives rise to lens, corneal epithelium, and eyelid skin.
• Mesoderm: Forms extraocular muscles and vascular components of the eye.
• Neural Crest Cells: Contribute to corneal stroma, sclera, choroid, and ciliary muscles.
Lead Question - 2014
Optic cup is derived from ?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation:
The optic cup is derived from the neural ectoderm, which originates as an outpouching from the diencephalon. The outer layer of the optic cup becomes the pigmented layer of the retina, and the inner layer forms the neural retina. This dual-layered cup induces lens formation from surface ectoderm. Thus, the correct answer is Neural ectoderm.
1) The lens of the eye is derived from?
a) Surface ectoderm
b) Neural ectoderm
c) Neural crest
d) Mesoderm
Explanation: The crystalline lens develops from the surface ectoderm, which forms the lens placode in response to induction from the optic vesicle. This placode invaginates to form the lens vesicle. Thus, the correct answer is Surface ectoderm.
2) The retina is derived from?
a) Surface ectoderm
b) Neural ectoderm
c) Neural crest
d) Mesoderm
Explanation: Both the neural and pigmented layers of the retina originate from the neural ectoderm, which forms the optic vesicle and subsequently the optic cup. Therefore, the correct answer is Neural ectoderm.
3) Corneal endothelium develops from?
a) Neural crest cells
b) Neural ectoderm
c) Mesoderm
d) Surface ectoderm
Explanation: Neural crest cells migrate between the lens and surface ectoderm to form the corneal endothelium and stroma. The corneal epithelium arises from surface ectoderm. Thus, the correct answer is Neural crest cells.
4) Which of the following eye structures arises from mesoderm?
a) Iris
b) Lens
c) Extraocular muscles
d) Retina
Explanation: The extraocular muscles and blood vessels of the eye arise from mesoderm, contributing to movement and vascularization of the eye. Hence, the correct answer is Extraocular muscles.
5) A defect in closure of the optic fissure leads to?
a) Anophthalmos
b) Coloboma
c) Cyclopia
d) Glaucoma
Explanation: Failure of the embryonic optic fissure to close results in coloboma, a keyhole-shaped defect in the iris, retina, or choroid. This occurs during the 5th week of development. Thus, the correct answer is Coloboma.
6) A baby born with absence of lens most likely had developmental failure of?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation: The lens develops from the surface ectoderm via the lens placode. Failure of placode induction or invagination results in congenital aphakia (absence of lens). Thus, the correct answer is Surface ectoderm.
7) Which structure induces lens formation in the embryo?
a) Optic cup
b) Surface ectoderm
c) Neural crest
d) Mesoderm
Explanation: The optic cup derived from neural ectoderm induces the overlying surface ectoderm to form the lens placode through epithelial-mesenchymal interactions. Thus, the correct answer is Optic cup.
8) The sclera and choroid are derived from?
a) Surface ectoderm
b) Mesoderm and neural crest
c) Neural ectoderm
d) Endoderm
Explanation: The sclera and choroid develop mainly from neural crest cells, with mesodermal contribution to vascular structures. They form the fibrous and vascular coats of the eyeball. Hence, the correct answer is Mesoderm and neural crest.
9) A neonate presents with a cleft in the iris and retina. The developmental cause is?
a) Failure of lens vesicle separation
b) Persistence of hyaloid artery
c) Nonclosure of optic fissure
d) Overgrowth of choroid
Explanation: Nonclosure of the embryonic optic fissure results in coloboma affecting iris or retina. It manifests as a characteristic cleft defect. Thus, the correct answer is Nonclosure of optic fissure.
10) Neural crest cells contribute to which ocular structure?
a) Corneal stroma
b) Lens capsule
c) Retina
d) Iris epithelium
Explanation: Neural crest cells form corneal stroma, corneal endothelium, sclera, and ciliary muscles. They do not contribute to retina or lens. Hence, the correct answer is Corneal stroma.
Chapter: Embryology; Topic: Development of Pharyngeal Arches; Subtopic: Derivatives of Pharyngeal Arches
Keyword Definitions:
• Pharyngeal Arches: Series of tissue bands in the embryonic head and neck that give rise to structures of the face, neck, and pharynx.
• Malleus and Incus: Middle ear ossicles responsible for sound transmission.
• Mandibular Arch (First Arch): The first pharyngeal arch forming mandible, malleus, incus, and associated muscles.
• Meckel’s Cartilage: Cartilage within the first arch forming malleus and incus.
• Stapes: Derived from the second pharyngeal arch (Reichert’s cartilage).
Lead Question - 2014
Malleus and incus are derived from ?
a) 1st Arch
b) 2nd Arch
c) 3rd Arch
d) 4th Arch
Explanation:
The malleus and incus arise from Meckel’s cartilage of the first pharyngeal (mandibular) arch. This arch gives rise to structures such as the mandible, malleus, incus, and associated muscles like tensor tympani. The stapes and styloid process originate from the second arch. Hence, the correct answer is 1st Arch.
1) Stapes is derived from?
a) 1st Arch
b) 2nd Arch
c) 3rd Arch
d) 4th Arch
Explanation: The stapes, styloid process, and part of the hyoid bone develop from the second (hyoid) arch, also called Reichert’s cartilage. This arch contributes to facial muscles and structures related to the stapes. Thus, the correct answer is 2nd Arch.
2) Meckel’s cartilage contributes to formation of?
a) Hyoid bone
b) Mandible
c) Stapes
d) Styloid process
Explanation: Meckel’s cartilage, derived from the first pharyngeal arch, acts as a template for the mandible. The anterior ligament of malleus and sphenomandibular ligament also arise from it. Thus, the correct answer is Mandible.
3) Which muscle is derived from the first pharyngeal arch?
a) Stylopharyngeus
b) Buccinator
c) Tensor tympani
d) Cricothyroid
Explanation: The first pharyngeal arch gives rise to the muscles of mastication (masseter, temporalis, pterygoids), mylohyoid, anterior belly of digastric, and tensor tympani. Hence, the correct answer is Tensor tympani.
4) Nerve supply of first pharyngeal arch?
a) Facial nerve
b) Mandibular nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The mandibular division of the trigeminal nerve (CN V3) supplies all muscles derived from the first pharyngeal arch, including the muscles of mastication and tensor tympani. Thus, the correct answer is Mandibular nerve.
5) The second pharyngeal arch cartilage is called?
a) Meckel’s cartilage
b) Reichert’s cartilage
c) Thyroid cartilage
d) Cricoid cartilage
Explanation: The second arch cartilage is known as Reichert’s cartilage. It forms the stapes, styloid process, stylohyoid ligament, and upper part of the hyoid bone. Hence, the correct answer is Reichert’s cartilage.
6) A newborn with micrognathia and malformed malleus likely has a defect in?
a) 1st Arch
b) 2nd Arch
c) 3rd Arch
d) 4th Arch
Explanation: Both the mandible and malleus develop from the first arch. Micrognathia and malformed malleus therefore indicate a first pharyngeal arch developmental anomaly. Thus, the correct answer is 1st Arch.
7) Muscles of facial expression arise from?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The muscles of facial expression, including orbicularis oculi and buccinator, originate from the second pharyngeal (hyoid) arch. They are innervated by the facial nerve (CN VII). Therefore, the correct answer is Second arch.
8) Third pharyngeal arch gives rise to?
a) Styloid process
b) Greater horn of hyoid
c) Cricoid cartilage
d) Mandible
Explanation: The third arch contributes to the greater horn and lower part of the hyoid bone and the stylopharyngeus muscle. The glossopharyngeal nerve (CN IX) innervates this arch. Thus, the correct answer is Greater horn of hyoid.
9) A child with facial paralysis and absence of stapes development has a defect in?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The facial nerve (CN VII) and stapes both derive from the second pharyngeal arch. Hence, congenital absence of stapes with facial paralysis suggests second arch abnormality. The correct answer is Second arch.
10) Derivatives of fourth pharyngeal arch include?
a) Muscles of mastication
b) Stylopharyngeus
c) Cricothyroid
d) Mylohyoid
Explanation: The fourth arch forms cricothyroid, levator veli palatini, and pharyngeal constrictors. It is supplied by the superior laryngeal branch of the vagus nerve. Hence, the correct answer is Cricothyroid.
Chapter: Embryology; Topic: Development of Tooth; Subtopic: Origin and Differentiation of Dental Structures
Keyword Definitions:
Dental Papilla: A condensation of ectomesenchymal cells beneath the enamel organ that forms dentin and pulp of the tooth.
Enamel Organ: An epithelial structure that gives rise to enamel-producing ameloblasts.
Dentin: Hard tissue beneath the enamel formed by odontoblasts derived from the dental papilla.
Dental Follicle: Connective tissue surrounding the developing tooth germ that gives rise to cementum and periodontal ligament.
Lead Question - 2014
Dental papilla give rise to ?
a) Enamel
b) Dental cuticle
c) Tooth pulp
d) None
Explanation: The dental papilla gives rise to dentin and the tooth pulp. It is derived from ectomesenchymal cells of the neural crest. Odontoblasts within the dental papilla secrete dentin, while the central cells remain as pulp. The enamel, however, arises from the enamel organ, not the dental papilla.
1) Which structure forms enamel of the tooth?
a) Dental papilla
b) Enamel organ
c) Dental follicle
d) Odontoblasts
Explanation: Enamel is formed by ameloblasts, which arise from the inner enamel epithelium of the enamel organ. It is the hardest tissue in the human body and is non-regenerative once formed. In contrast, dentin and pulp are derived from the dental papilla.
2) Clinical-type: In a child with dentinogenesis imperfecta, which embryonic structure is defective?
a) Dental papilla
b) Enamel organ
c) Dental follicle
d) Buccal mucosa epithelium
Explanation: Dentinogenesis imperfecta involves defective dentin formation due to abnormal odontoblast function from the dental papilla. The result is translucent teeth with weak structural integrity. Enamel remains normal but fractures easily because of poor dentin support.
3) The dental follicle gives rise to -
a) Enamel
b) Dentin
c) Cementum
d) Pulp
Explanation: The dental follicle forms the cementum, periodontal ligament, and alveolar bone. These supporting structures collectively form the periodontium. The follicle originates from surrounding ectomesenchymal tissue and plays a key role in tooth eruption and anchoring.
4) Clinical-type: A 7-year-old boy shows a radiolucent lesion around a tooth crown. Histology reveals remnants of enamel organ. The lesion is likely -
a) Dental cyst
b) Ameloblastoma
c) Dentigerous cyst
d) Odontoma
Explanation: A dentigerous cyst originates from remnants of the enamel organ around the crown of unerupted teeth. It is an odontogenic cyst associated with the reduced enamel epithelium. Dental papilla or follicle remnants can contribute to such developmental pathologies.
5) The cells that form dentin are known as -
a) Odontoblasts
b) Ameloblasts
c) Cementoblasts
d) Osteoblasts
Explanation: Odontoblasts form dentin and are derived from the outer cells of the dental papilla. These cells deposit predentin that later mineralizes. Once dentin formation begins, ameloblasts from the enamel organ form enamel in a reciprocal induction process.
6) Clinical-type: A tooth with exposed dentin but intact pulp indicates injury to which layer?
a) Enamel
b) Pulp
c) Cementum
d) Periodontal ligament
Explanation: Exposure of dentin occurs when the enamel is eroded or lost due to trauma or caries. The dentin arises from odontoblasts of the dental papilla, while the pulp remains unexposed initially. Prolonged exposure may lead to pulp inflammation (pulpitis).
7) The dental papilla is derived from which embryonic origin?
a) Endoderm
b) Mesoderm
c) Neural crest ectomesenchyme
d) Surface ectoderm
Explanation: The dental papilla originates from neural crest-derived ectomesenchyme. These specialized cells migrate into the developing jaw region, giving rise to odontoblasts and pulp tissue. This neural crest origin explains the tooth’s sensitivity and neurovascular connections.
8) Clinical-type: A patient has enamel hypoplasia but normal dentin. Which part was defective during development?
a) Dental papilla
b) Enamel organ
c) Dental follicle
d) Periodontal membrane
Explanation: Enamel hypoplasia results from defective ameloblasts in the enamel organ. The dental papilla, responsible for dentin and pulp, remains unaffected. Causes include nutritional deficiency, trauma, or systemic disease during tooth development.
9) Which component of the tooth is of ectodermal origin?
a) Enamel
b) Dentin
c) Cementum
d) Pulp
Explanation: Enamel is the only tooth structure derived from ectoderm, formed by ameloblasts from the enamel organ. In contrast, dentin, pulp, and cementum are mesenchymal derivatives from neural crest ectomesenchyme.
10) Clinical-type: In tooth regeneration research, stem cells are derived from which embryonic component to form pulp-like tissue?
a) Enamel organ
b) Dental papilla
c) Dental follicle
d) Buccal epithelium
Explanation: Dental stem cells with regenerative potential are obtained from the dental papilla. These cells can differentiate into odontoblast-like and pulp-like tissues. This discovery supports advances in regenerative dentistry, helping in pulp repair and tissue engineering.
Chapter: Embryology; Topic: Early Development of Embryo; Subtopic: Cleavage and Morula Formation
Keyword Definitions:
Morula: A solid ball of blastomeres formed after cleavage, usually consisting of 16 cells before transforming into the blastocyst.
Cleavage: Rapid mitotic divisions of the zygote without growth, producing smaller cells called blastomeres.
Blastocyst: A hollow structure formed from the morula, consisting of an inner cell mass and trophoblast.
Blastomere: Individual cells formed during the cleavage of the zygote.
Lead Question - 2014
Morula is how many celled -
a) 4
b) 8
c) 12
d) 16
Explanation: The morula is typically a 16-celled stage of embryonic development formed after several cleavage divisions of the zygote. It appears around the 3rd day after fertilization, resembling a mulberry. The cells (blastomeres) of the morula are compacted together through tight junctions, leading to differentiation into inner and outer cell masses that form the blastocyst.
1) The blastocyst stage is formed on which day after fertilization?
a) 2nd day
b) 4th day
c) 6th day
d) 8th day
Explanation: The blastocyst forms on the 4th day after fertilization when the morula develops a fluid-filled cavity known as the blastocoel. The inner cell mass becomes the embryo proper, while the trophoblast develops into the placenta. This stage implants into the uterine wall by day 6–7.
2) The process of compaction during cleavage results in -
a) Formation of blastomeres
b) Formation of morula
c) Differentiation of inner and outer cells
d) Implantation
Explanation: Compaction occurs at the 8-cell stage, resulting in tight junctions between blastomeres that differentiate into inner and outer cells, forming the morula. This structural reorganization establishes polarity, preparing the embryo for blastocyst formation and implantation readiness.
3) Clinical-type: A 3-day-old embryo in fallopian tube shows 16 cells. What is this stage called?
a) Zygote
b) Blastocyst
c) Morula
d) Gastrula
Explanation: A 3-day-old embryo with 16 cells represents the morula stage. It travels through the fallopian tube before entering the uterus. The compacted blastomeres prepare for differentiation into inner and outer layers, marking the first step toward formation of the blastocyst.
4) The outer cell mass of the blastocyst forms -
a) Embryo proper
b) Amniotic cavity
c) Trophoblast
d) Neural tube
Explanation: The outer cell mass of the blastocyst forms the trophoblast, which contributes to the development of the placenta. The trophoblast later differentiates into cytotrophoblast and syncytiotrophoblast, essential for implantation and nutrient exchange.
5) Clinical-type: A woman has ectopic pregnancy; the implanted stage observed was a blastocyst. Which stage preceded it?
a) Morula
b) Gastrula
c) 8-cell stage
d) Zygote
Explanation: The morula precedes the blastocyst stage. In ectopic pregnancy, this morula undergoes abnormal implantation in the fallopian tube. It marks an early post-cleavage phase before the blastocoel cavity forms, leading to trophoblast differentiation and eventual abnormal fixation.
6) The inner cell mass of blastocyst forms -
a) Embryo proper
b) Placenta
c) Amniotic fluid
d) Decidua
Explanation: The inner cell mass forms the embryo proper and extraembryonic membranes. It gives rise to all three germ layers — ectoderm, mesoderm, and endoderm. These layers later form organs, tissues, and body systems, marking it as a key step in embryogenesis.
7) Clinical-type: During IVF, an embryo ready for uterine transfer shows 16 cells. Which term describes it?
a) Zygote
b) Blastocyst
c) Morula
d) Gastrula
Explanation: A 16-celled embryo observed during in vitro fertilization corresponds to the morula stage. This is ideal for uterine transfer because it ensures early implantation success and correct endometrial synchronization. It indicates active cleavage with compacted cells prior to blastulation.
8) The zygote undergoes its first cleavage after how many hours?
a) 6 hours
b) 12 hours
c) 24 hours
d) 36 hours
Explanation: The first cleavage of the zygote occurs at approximately 24 hours post-fertilization, resulting in two blastomeres. This marks the beginning of rapid mitotic divisions that will ultimately lead to the morula and blastocyst stages, essential for implantation.
9) Clinical-type: A biopsy from early conceptus shows outer trophoblastic cells and inner mass. The developmental stage is -
a) Morula
b) Blastocyst
c) Gastrula
d) Neurula
Explanation: The described structure represents a blastocyst, characterized by a trophoblast and an inner cell mass. The trophoblast later invades the endometrium during implantation. This stage follows the morula, signifying the start of differentiation and cavity formation.
10) Zona pellucida is lost during which stage?
a) 2-cell stage
b) Morula
c) Blastocyst
d) Gastrula
Explanation: The zona pellucida is shed during the blastocyst stage in a process called hatching. This allows implantation into the uterine wall. The morula remains within the zona pellucida until fluid accumulation and expansion trigger the formation of the blastocyst cavity.
Chapter: Neuroanatomy; Topic: Brainstem; Subtopic: Developmental Origin of Medulla Oblongata
Keyword Definitions:
Medulla oblongata: The lower part of the brainstem responsible for autonomic functions like respiration, heart rate, and blood pressure.
Myelencephalon: The posterior part of the embryonic hindbrain that gives rise to the medulla oblongata.
Brainstem: The central trunk of the brain connecting the cerebrum with the spinal cord.
Embryonic vesicles: Developmental brain regions — prosencephalon, mesencephalon, and rhombencephalon — that differentiate into various brain structures.
Lead Question - 2014
Medulla oblongata is derived from ?
a) Telencephalon
b) Diencephalon
c) Mesencephalon
d) Myelencephalon
Explanation: The medulla oblongata develops from the myelencephalon, the caudal part of the rhombencephalon (hindbrain). During embryonic development, the rhombencephalon divides into the metencephalon (forming the pons and cerebellum) and the myelencephalon (forming the medulla). The medulla controls vital autonomic functions like heart rate, respiration, and reflexes such as coughing and vomiting.
1) The pons is derived from ?
a) Metencephalon
b) Myelencephalon
c) Diencephalon
d) Mesencephalon
Explanation: The pons originates from the metencephalon, the upper division of the rhombencephalon. It serves as a communication bridge between the cerebrum and cerebellum. Functionally, it assists in respiratory control and facial sensation. During embryogenesis, neural tube segmentation determines these structures' distinct developmental origins.
2) The midbrain originates from which embryonic vesicle?
a) Prosencephalon
b) Mesencephalon
c) Diencephalon
d) Rhombencephalon
Explanation: The midbrain arises from the mesencephalon. It contains important structures such as the superior and inferior colliculi, red nucleus, and substantia nigra. These regions regulate visual and auditory reflexes and coordinate motor control, linking sensory input to motor output through cranial nerve nuclei and tracts.
3) Clinical-type: A patient with lesions in the medulla shows respiratory arrest. Which embryonic structure was primarily affected?
a) Telencephalon
b) Myelencephalon
c) Mesencephalon
d) Metencephalon
Explanation: The myelencephalon forms the medulla oblongata, housing the respiratory and cardiac centers. Lesions here result in life-threatening respiratory and cardiovascular dysfunction. The medulla integrates autonomic signals and transmits them via cranial nerves IX, X, XI, and XII to maintain homeostasis.
4) The cerebellum develops from ?
a) Metencephalon
b) Myelencephalon
c) Mesencephalon
d) Diencephalon
Explanation: The cerebellum arises from the metencephalon during neural tube development. It plays a crucial role in balance, posture, and coordination. The cerebellar hemispheres form from dorsal outgrowths of the metencephalon, developing the vermis and cerebellar cortex for fine motor control.
5) Clinical-type: Damage to the olive of medulla affects which function?
a) Auditory processing
b) Coordination
c) Taste
d) Smell
Explanation: The inferior olivary nucleus in the medulla assists cerebellar coordination by relaying sensory and motor information. Lesions disrupt timing and precision of movements, causing ataxia. This nucleus originates embryologically within the myelencephalon, confirming its role in medullary circuitry.
6) The diencephalon gives rise to ?
a) Thalamus and hypothalamus
b) Pons and medulla
c) Cerebral cortex
d) Midbrain
Explanation: The diencephalon forms structures like the thalamus, hypothalamus, epithalamus, and subthalamus. These regulate sensory relay, endocrine control, and autonomic functions. Positioned between the midbrain and telencephalon, it plays a central role in sensory integration and emotional processing via hypothalamic connections.
7) Clinical-type: A newborn with Arnold–Chiari malformation shows medullary herniation. Which embryonic part was affected?
a) Myelencephalon
b) Metencephalon
c) Telencephalon
d) Mesencephalon
Explanation: Arnold–Chiari malformation involves herniation of medulla (derived from myelencephalon) into the foramen magnum, compressing brainstem structures. This congenital defect leads to respiratory and swallowing issues, reflecting the medulla’s role in autonomic and cranial nerve function.
8) Which of the following is not derived from the rhombencephalon?
a) Pons
b) Cerebellum
c) Medulla
d) Midbrain
Explanation: The midbrain develops from the mesencephalon, not the rhombencephalon. The rhombencephalon gives rise to the pons, cerebellum, and medulla, collectively forming the hindbrain responsible for coordination, autonomic control, and reflex activity.
9) Clinical-type: A patient with loss of gag reflex has lesion in which structure derived from myelencephalon?
a) Nucleus ambiguus
b) Red nucleus
c) Substantia nigra
d) Thalamus
Explanation: The nucleus ambiguus in the medulla, derived from the myelencephalon, controls muscles of the pharynx and larynx via cranial nerves IX and X. Lesions impair the gag reflex, swallowing, and phonation. This highlights the medulla’s role in cranial nerve integration.
10) The telencephalon develops into ?
a) Cerebral hemispheres
b) Pons
c) Midbrain
d) Cerebellum
Explanation: The telencephalon forms the cerebral hemispheres, basal ganglia, and olfactory bulbs. These structures handle higher cognitive, emotional, and voluntary motor functions. As the most anterior brain vesicle, it develops from the prosencephalon during week five of embryonic development.
Topic: Development of Kidneys and Their Blood Supply; Subtopic: Embryological Origin of Renal Arteries
Keyword Definitions:
Renal Arteries: Paired arteries arising from the abdominal aorta to supply the kidneys.
Common Iliac Artery: One of the terminal branches of the abdominal aorta dividing into internal and external iliac arteries.
Mesonephros: The embryonic kidney that functions temporarily before the metanephros develops.
Metanephros: The definitive kidney, developing in the pelvis and ascending during fetal life.
Aorta: The main arterial trunk supplying oxygenated blood to the systemic circulation.
Lead Question – 2014
Initially, renal arteries are branches of?
a) Internal pudendal artery
b) External iliac artery
c) Common iliac artery
d) Aorta
Explanation: In early embryonic life, kidneys develop in the pelvic region and receive their blood supply from branches of the common iliac arteries. As kidneys ascend, their arterial supply shifts sequentially to higher levels, finally deriving from the abdominal aorta. The transient arteries regress as the kidney ascends. Hence, the correct answer is c) Common iliac artery.
1. During kidney ascent, which artery becomes the final source of its blood supply?
a) Common iliac artery
b) Abdominal aorta
c) Internal iliac artery
d) Median sacral artery
Explanation: Initially supplied by branches from the common iliac artery, the kidney ascends to the lumbar region where it ultimately receives blood from the abdominal aorta. Lower vessels regress, and the renal arteries from the aorta become the definitive arterial supply. Therefore, the correct answer is b) Abdominal aorta.
2. Accessory renal arteries arise due to:
a) Failure of regression of primitive renal arteries
b) Abnormal division of the aorta
c) Persistent mesonephric arteries
d) Recanalization defects
Explanation: Accessory renal arteries result from the persistence of embryonic renal arteries that normally regress as the kidney ascends. They may arise from the aorta or iliac arteries and are common anatomical variations. These vessels are functionally important and supply specific kidney segments. Thus, the correct answer is a) Failure of regression of primitive renal arteries.
3. The kidney ascends from the pelvis to the lumbar region during which week of development?
a) 3rd week
b) 4th–5th week
c) 6th–9th week
d) 10th–12th week
Explanation: The metanephric kidneys initially lie in the pelvic region and ascend to their lumbar position between the 6th and 9th weeks of gestation. The ascent is due to body growth and decreased curvature of the embryo. Hence, the correct answer is c) 6th–9th week.
4. A patient with a pelvic kidney has its arterial supply most likely from:
a) Abdominal aorta
b) Common iliac artery
c) Superior mesenteric artery
d) Inferior mesenteric artery
Explanation: A pelvic kidney results when the kidney fails to ascend during development. It retains its early blood supply from the common iliac artery. The renal vessels are shorter, and this anomaly is often incidental but may cause ureteral obstruction. The correct answer is b) Common iliac artery.
5. During embryonic development, which structure gives rise to the definitive kidney?
a) Pronephros
b) Mesonephros
c) Metanephros
d) Wolffian duct
Explanation: The metanephros forms the permanent kidney. It appears in the 5th week, derived from the ureteric bud (collecting system) and metanephric blastema (nephrons). The pronephros and mesonephros regress. Thus, the answer is c) Metanephros.
6. (Clinical) An aberrant renal artery crossing the ureter anteriorly may cause:
a) Hydronephrosis
b) Renal vein thrombosis
c) Pyelonephritis
d) Renal failure
Explanation: An aberrant renal artery may cross the ureter anteriorly, compressing it and obstructing urine flow, leading to hydronephrosis. This condition causes flank pain and renal pelvis dilation visible on imaging. Thus, the correct answer is a) Hydronephrosis.
7. (Clinical) A 30-year-old male with pelvic kidney presents with hematuria. Imaging shows accessory arteries from the common iliac. The cause is:
a) Ectopic kidney with persistent early blood supply
b) Renal artery stenosis
c) Inferior mesenteric artery aneurysm
d) Abnormal ureteral insertion
Explanation: A pelvic kidney receives its blood supply from the arteries at its developmental level, usually the common iliac. Persistence of embryonic vessels leads to multiple accessory arteries. Hence, the correct answer is a) Ectopic kidney with persistent early blood supply.
8. (Clinical) A patient undergoing renal transplantation has the donor renal artery anastomosed with:
a) Internal iliac artery
b) Common iliac artery
c) External iliac artery
d) Inferior epigastric artery
Explanation: In renal transplantation, the donor renal artery is usually anastomosed to the external iliac artery because of its accessibility and size match. The renal vein is connected to the external iliac vein. This provides optimal graft perfusion. Therefore, the correct answer is c) External iliac artery.
9. (Clinical) During aortic aneurysm repair, which artery must be preserved to maintain kidney perfusion?
a) Mesenteric artery
b) Renal artery
c) Lumbar artery
d) Celiac trunk
Explanation: The kidneys are supplied by the renal arteries directly from the abdominal aorta. During aneurysm repair near the renal hilum, preserving these arteries is crucial to prevent renal ischemia or infarction. Hence, the correct answer is b) Renal artery.
10. (Clinical) A 40-year-old patient with renovascular hypertension is found to have stenosis of the renal artery. The cause of hypertension is due to:
a) Increased renin release
b) Decreased angiotensin II
c) Low aldosterone
d) Increased GFR
Explanation: Renal artery stenosis reduces renal perfusion pressure, stimulating the juxtaglomerular cells to release renin. This activates the renin-angiotensin-aldosterone system, increasing blood pressure. Hence, renovascular hypertension develops. The correct answer is a) Increased renin release.
Chapter: Embryology
Topic: Fertilization and Implantation
Subtopic: Time of Implantation
Keyword Definitions:
• Fertilization: Fusion of sperm and ovum forming a zygote.
• Implantation: Process where blastocyst embeds into the endometrium.
• Blastocyst: Early embryonic stage consisting of inner cell mass and trophoblast.
• Endometrium: Uterine lining prepared for embryo implantation.
• Trophoblast: Outer cell layer of blastocyst involved in implantation.
• Luteal phase: Phase of menstrual cycle dominated by progesterone.
• hCG: Hormone secreted by trophoblast to support pregnancy.
• Zona pellucida: Glycoprotein covering around ovum preventing polyspermy.
• Morula: Solid ball of blastomeres formed before blastocyst stage.
• Decidua: Endometrium during pregnancy responding to implantation.
Lead Question - 2013
Implantation occurs after how many days of fertilization?
a) 3-5 days
b) 5-7 days
c) 7-9 days
d) > 14 days
Explanation: Implantation occurs typically on the 6th or 7th day after fertilization, when the blastocyst penetrates the endometrium. Fertilization occurs in the ampulla, cleavage forms morula, which develops into a blastocyst by day 4-5, and implantation begins by day 6-7. Correct answer: 7-9 days (c).
1) Cleavage of zygote results in formation of:
a) Blastocyst
b) Morula
c) Trophoblast
d) Decidua
Explanation: Cleavage is the rapid mitotic division of zygote forming a morula around day 3. The morula later develops into a blastocyst. This process is essential for implantation. Correct answer: Morula (b).
2) Clinical case: A woman with luteal phase defect may have recurrent implantation failure due to deficiency of:
a) Estrogen
b) Progesterone
c) LH
d) FSH
Explanation: Progesterone secreted by corpus luteum maintains endometrium. In luteal phase defect, low progesterone leads to implantation failure and infertility. Treatment involves progesterone supplementation. Correct answer: Progesterone (b).
3) Zona pellucida prevents:
a) Cleavage
b) Polyspermy
c) Fertilization
d) Ovulation
Explanation: Zona pellucida is a glycoprotein coat around the ovum that blocks multiple sperm entry after fertilization by cortical reaction. This ensures normal chromosomal complement. Correct answer: Polyspermy (b).
4) Clinical case: A patient with ectopic pregnancy most commonly shows implantation at:
a) Ampulla
b) Isthmus
c) Cervix
d) Ovary
Explanation: Most ectopic pregnancies occur in the fallopian tube, especially the ampullary region. This abnormal implantation is life-threatening and requires urgent management. Correct answer: Ampulla (a).
5) Hormone responsible for endometrial preparation for implantation:
a) Progesterone
b) Estrogen
c) LH
d) Prolactin
Explanation: Progesterone secreted by corpus luteum converts proliferative endometrium into secretory endometrium, suitable for implantation. Estrogen only stimulates proliferation but progesterone maintains pregnancy. Correct answer: Progesterone (a).
6) Clinical case: A woman develops vaginal bleeding 8 days post-ovulation. This corresponds to:
a) Follicular phase
b) Ovulatory phase
c) Implantation bleeding
d) Menstrual bleeding
Explanation: Implantation bleeding may occur around 7–9 days after ovulation, due to invasion of blastocyst into endometrium and disruption of blood vessels. Correct answer: Implantation bleeding (c).
7) Trophoblast differentiates into:
a) Cytotrophoblast and syncytiotrophoblast
b) Epiblast and hypoblast
c) Morula and blastocyst
d) Decidua and chorion
Explanation: Trophoblast cells of blastocyst differentiate into cytotrophoblast and syncytiotrophoblast, which play roles in implantation and hormone secretion (hCG). Correct answer: Cytotrophoblast and syncytiotrophoblast (a).
8) Clinical case: hCG is detected in maternal blood earliest by:
a) 1 day post-fertilization
b) 4 days post-fertilization
c) 8-9 days post-fertilization
d) 20 days post-fertilization
Explanation: Syncytiotrophoblast secretes hCG once implantation begins, which can be detected in maternal blood about 8-9 days after fertilization. Correct answer: 8-9 days (c).
9) The decidua basalis contributes to formation of:
a) Chorionic villi
b) Placenta
c) Amnion
d) Yolk sac
Explanation: The decidua basalis is the part of maternal endometrium directly beneath the implanted blastocyst. It fuses with chorionic villi to form the placenta. Correct answer: Placenta (b).
10) Clinical case: A woman on day 21 of her menstrual cycle shows endometrium with coiled glands and glycogen. This indicates:
a) Follicular phase
b) Proliferative phase
c) Secretory phase
d) Menstrual phase
Explanation: On day 21, progesterone action makes the endometrium secretory, preparing for implantation. Glands are coiled and glycogen-rich. Correct answer: Secretory phase (c).
Keyword Definitions
• Spleen – Lymphoid organ in left upper abdomen; filters blood, immune surveillance, stores blood.
• White pulp – Lymphoid tissue surrounding central arteries; contains lymphocytes; immune function.
• Red pulp – Vascular sinusoids and cords; removes aged RBCs, stores platelets.
• Billroth’s cords – Also called splenic cords; connective tissue strands in red pulp containing macrophages, lymphocytes, and plasma cells.
• Central artery – Penetrates white pulp; surrounded by periarteriolar lymphoid sheath (PALS).
• Splenic sinusoids – Vascular channels in red pulp; allow filtration of blood cells.
• Capsule – Dense connective tissue surrounding spleen; provides protection and structure.
• Clinical relevance – Splenic injury affects hematological and immune function; red pulp disorders cause anemia.
• Embryology – Spleen develops from mesenchymal cells in dorsal mesogastrium during 5th week.
• Histology – Red pulp: cords and sinusoids; White pulp: lymphoid follicles with germinal centers.
Chapter: Histology / Embryology
Topic: Lymphoid Organs
Subtopic: Spleen Structure and Components
Lead Question – 2013
Billroth's cord are present in which part of spleen?
a) White pulp
b) Red pulp
c) Both
d) Capsule
Explanation: Billroth’s cords are connective tissue strands found in the red pulp of the spleen, containing macrophages, lymphocytes, plasma cells, and reticular fibers. Correct answer: Red pulp. They function in filtration and immune surveillance. White pulp contains lymphoid follicles; capsule is protective connective tissue. Damage can impair hematological and immune functions.
Guessed Questions for NEET PG
1) Central arteries are found in:
a) White pulp
b) Red pulp
c) Both
d) Capsule
Explanation: Central arteries pass through white pulp surrounded by periarteriolar lymphoid sheath (PALS). Correct answer: White pulp. Clinical: arterial occlusion can reduce immune cell activation.
2) Splenic sinusoids are located in:
a) Red pulp
b) White pulp
c) Capsule
d) Trabeculae
Explanation: Sinusoids are vascular channels in red pulp facilitating filtration of aged or damaged RBCs. Correct answer: Red pulp. Clinical: sinusoidal damage can lead to hemolytic anemia.
3) Periarteriolar lymphoid sheath (PALS) surrounds:
a) Central arteries
b) Red pulp cords
c) Capsule
d) Sinusoids
Explanation: PALS consists of T-lymphocytes surrounding central arteries in white pulp. Correct answer: Central arteries. Clinical: immune deficiencies can impair T-cell mediated responses.
4) Germinal centers are present in:
a) White pulp follicles
b) Red pulp
c) Capsule
d) Sinusoids
Explanation: Germinal centers in white pulp follicles are sites of B-cell proliferation and differentiation. Correct answer: White pulp. Clinical: germinal center hyperplasia occurs in infections or autoimmune diseases.
5) Trabeculae of spleen contain:
a) Connective tissue and vessels
b) White pulp only
c) Red pulp only
d) Sinusoids only
Explanation: Trabeculae provide structural support, carrying arteries and veins into spleen. Correct answer: Connective tissue and vessels. Clinical: trauma can rupture trabeculae, causing hemorrhage.
6) Macrophages in red pulp function to:
a) Phagocytose aged RBCs
b) Produce antibodies
c) Secrete collagen
d) Form germinal centers
Explanation: Macrophages in Billroth’s cords phagocytose old erythrocytes and pathogens. Correct answer: Phagocytose aged RBCs. Clinical: macrophage dysfunction leads to splenomegaly and anemia.
7) White pulp is rich in:
a) Lymphocytes
b) Erythrocytes
c) Platelets
d) Sinusoids
Explanation: White pulp contains lymphocytes around central arteries for immune surveillance. Correct answer: Lymphocytes. Clinical: loss leads to immunodeficiency.
8) Red pulp ratio to white pulp is approximately:
a) 3:1
b) 1:1
c) 1:3
d) 2:1
Explanation: Red pulp constitutes roughly 3/4 of splenic volume, responsible for filtration and blood storage. Correct answer: 3:1. Clinical: splenomegaly increases red pulp proportion causing anemia.
9) Capsule of spleen is composed of:
a) Dense connective tissue
b) Lymphoid tissue
c) Sinusoids
d) Cartilage
Explanation: Capsule is dense connective tissue surrounding spleen, providing protection and support. Correct answer: Dense connective tissue. Clinical: splenic rupture involves capsule laceration.
10) Accessory spleens are usually located near:
a) Hilum
b) Red pulp
c) White pulp
d) Capsule
Explanation: Accessory spleens develop near hilum, containing red and white pulp. Correct answer: Hilum. Clinically important in splenectomy to remove all functional splenic tissue.
Keyword Definitions
• Cartilage – Flexible connective tissue present in joints, rib cage, ear, nose, and respiratory tract.
• Hyaline cartilage – Most common cartilage; glassy matrix, found in nose, trachea, larynx, fetal skeleton, articular surfaces.
• Collagen types – Structural proteins; provide tensile strength. Type I (bone, tendon), Type II (cartilage), Type III (reticular), Type IV (basement membrane), Type V (cell surfaces).
• Type II collagen – Predominant in hyaline and elastic cartilage; forms fibrils providing resilience.
• Chondrocytes – Cartilage cells producing extracellular matrix including collagen and proteoglycans.
• Extracellular matrix – Gel-like substance containing collagen, proteoglycans, water; gives cartilage strength and elasticity.
• Articular cartilage – Covers joint surfaces; reduces friction; primarily hyaline cartilage.
• Clinical relevance – Collagen defects lead to skeletal dysplasia, osteoarthritis, or cartilage degeneration.
• Endochondral ossification – Process where hyaline cartilage is replaced by bone during fetal development.
• Cartilage repair – Limited due to avascularity; relies on chondrocytes and diffusion.
Chapter: Histology / Embryology
Topic: Connective Tissue
Subtopic: Cartilage Structure and Collagen Types
Lead Question – 2013
Collagen found in hyaline cartilage is?
a) Type I
b) Type II
c) Type IV
d) Type V
Explanation: Hyaline cartilage primarily contains type II collagen, forming fibrils that provide tensile strength and resilience to the extracellular matrix. Correct answer: Type II. Type I is in bone and tendon, Type IV in basement membrane, Type V in cell surfaces. Collagen defects can cause skeletal abnormalities or early osteoarthritis.
Guessed Questions for NEET PG
1) Elastic cartilage contains which type of collagen?
a) Type I
b) Type II
c) Type IV
d) Type V
Explanation: Elastic cartilage contains type II collagen along with abundant elastin fibers. Correct answer: Type II. Found in ear pinna and epiglottis. Clinical: defects in type II collagen lead to structural weakness and potential deformities.
2) Fibrocartilage contains predominant collagen:
a) Type I
b) Type II
c) Type IV
d) Type V
Explanation: Fibrocartilage is rich in type I collagen, giving it high tensile strength for intervertebral discs, menisci, and pubic symphysis. Correct answer: Type I. Clinical: degeneration leads to disc herniation and joint instability.
3) Articular cartilage in joints is primarily:
a) Hyaline
b) Elastic
c) Fibrocartilage
d) Atavistic
Explanation: Articular cartilage is hyaline type with type II collagen. Correct answer: Hyaline. Provides low-friction, resilient surfaces. Damage leads to osteoarthritis.
4) Collagen in basement membrane is:
a) Type I
b) Type II
c) Type IV
d) Type V
Explanation: Type IV collagen forms non-fibrillar network in basement membranes. Correct answer: Type IV. Clinical: defects cause Alport syndrome and kidney dysfunction.
5) Type II collagen defect causes:
a) Chondrodysplasia
b) Osteogenesis imperfecta
c) Ehlers-Danlos
d) Marfan
Explanation: Type II collagen mutation leads to chondrodysplasia, skeletal abnormalities, and early-onset osteoarthritis. Correct answer: Chondrodysplasia.
6) Proteoglycan in hyaline cartilage:
a) Aggrecan
b) Decorin
c) Fibronectin
d) Laminin
Explanation: Aggrecan is the major proteoglycan in hyaline cartilage, binding water and contributing to compressive strength. Correct answer: Aggrecan. Clinical: degradation leads to cartilage wear in arthritis.
7) Chondrocytes reside in:
a) Lacunae
b) Canaliculi
c) Haversian canals
d) Interstitial spaces
Explanation: Chondrocytes are housed in lacunae within the cartilage matrix. Correct answer: Lacunae. Clinical: chondrocyte death contributes to cartilage degeneration.
8) Cartilage avascularity implies:
a) Nutrients diffuse from perichondrium
b) Blood vessels penetrate matrix
c) Direct innervation
d) Lymphatic supply
Explanation: Cartilage receives nutrients by diffusion from the perichondrium. Correct answer: Nutrients diffuse from perichondrium. Clinical: slow healing of cartilage injuries.
9) Endochondral ossification replaces:
a) Hyaline cartilage
b) Fibrocartilage
c) Elastic cartilage
d) Bone marrow
Explanation: Hyaline cartilage serves as a template in endochondral ossification. Correct answer: Hyaline cartilage. Clinical: disturbances lead to growth plate disorders and short stature.
10) Nasal septum cartilage is:
a) Hyaline
b) Elastic
c) Fibrocartilage
d) Atavistic
Explanation: Nasal septum is hyaline cartilage with type II collagen. Correct answer: Hyaline. Clinical: trauma or septal perforation affects airflow and nasal support.
Keyword Definitions
• Epiphysis – Secondary ossification center at the end of long or irregular bones.
• Traction epiphysis – Develops at site of muscle or tendon attachment; ossification influenced by pulling forces.
• Pressure epiphysis – Forms at sites subjected to articular pressure, e.g., head of femur.
• Atavistic epiphysis – Rare, evolutionary remnant epiphysis; may not appear in all individuals.
• Aberrant epiphysis – Epiphysis occurring at unusual location, not typically present.
• Mastoid process – Part of temporal bone; develops as traction epiphysis for sternocleidomastoid attachment.
• Ossification – Process of bone formation, primary and secondary centers.
• Clinical relevance – Abnormal development leads to delayed ossification or deformity; relevant in surgery or trauma.
• Sternocleidomastoid – Muscle inserting on mastoid process; traction epiphysis responds to muscular forces.
• Embryology of skull – Bones form by intramembranous and endochondral ossification.
Chapter: Embryology
Topic: Skeletal System Development
Subtopic: Epiphysis Types and Development
Lead Question – 2013
Mastoid process is which type of epiphysis?
a) Pressure
b) Aberrant
c) Atavistic
d) Traction
Explanation: The mastoid process develops as a traction epiphysis where the sternocleidomastoid muscle attaches. Correct answer: Traction. Traction epiphyses form under tensile forces, unlike pressure epiphyses which develop under joint loading. Clinical relevance: mastoiditis or congenital hypoplasia can affect muscle function and cranial anatomy.
Guessed Questions for NEET PG
1) Head of femur is which epiphysis?
a) Traction
b) Pressure
c) Aberrant
d) Atavistic
Explanation: Head of femur is a pressure epiphysis, forming under joint load to articulate with acetabulum. Correct answer: Pressure. Clinical: Slipped capital femoral epiphysis occurs in adolescents due to weak epiphyseal plate.
2) Greater trochanter of femur is:
a) Traction epiphysis
b) Pressure epiphysis
c) Atavistic epiphysis
d) Aberrant epiphysis
Explanation: Greater trochanter forms a traction epiphysis at muscle attachment sites. Correct answer: Traction. Clinical: avulsion fractures may occur in athletic adolescents.
3) Sesamoid bones are considered:
a) Traction epiphysis
b) Aberrant epiphysis
c) Pressure epiphysis
d) Atavistic epiphysis
Explanation: Sesamoid bones (e.g., patella) develop under mechanical stress at tendon insertions, thus traction epiphyses. Correct answer: Traction epiphysis. Clinical: sesamoiditis causes forefoot pain.
4) Os trigonum of ankle is which type?
a) Aberrant
b) Atavistic
c) Pressure
d) Traction
Explanation: Os trigonum is an atavistic epiphysis, present in some individuals as a remnant accessory bone. Correct answer: Atavistic. Clinical: may cause posterior ankle impingement.
5) Calcaneal tuberosity is:
a) Pressure epiphysis
b) Traction epiphysis
c) Aberrant
d) Atavistic
Explanation: Calcaneal tuberosity is a traction epiphysis for Achilles tendon attachment. Correct answer: Traction. Clinical: Sever’s disease occurs here in adolescents with repetitive stress.
6) Epiphysis of distal tibia articulating with talus is:
a) Pressure
b) Traction
c) Aberrant
d) Atavistic
Explanation: The distal tibial epiphysis is a pressure epiphysis forming the ankle joint. Correct answer: Pressure. Clinical: trauma can cause growth disturbances leading to angular deformity.
7) Pisiform is classified as:
a) Traction
b) Pressure
c) Aberrant
d) Atavistic
Explanation: Pisiform is a traction epiphysis within tendon of flexor carpi ulnaris. Correct answer: Traction. Clinical: pisiform fractures are rare but affect wrist function.
8) Epiphysis absent in most individuals and variable is:
a) Atavistic
b) Traction
c) Pressure
d) Aberrant
Explanation: Atavistic epiphyses are evolutionary remnants, variable in occurrence. Correct answer: Atavistic. Clinical: accessory bones may be mistaken for fractures on X-ray.
9) Clavicular epiphysis in late adolescence is:
a) Traction
b) Pressure
c) Aberrant
d) Atavistic
Explanation: Clavicular epiphysis is a traction epiphysis forming for sternocleidomastoid and trapezius attachment. Correct answer: Traction. Clinical: delayed ossification may mimic fracture on imaging.
10) Patella develops as:
a) Traction epiphysis
b) Aberrant
c) Pressure epiphysis
d) Atavistic
Explanation: Patella is a traction epiphysis within quadriceps tendon. Correct answer: Traction. Clinical: Osgood-Schlatter-like stress affects traction epiphyses in lower limb.
Keyword Definitions
• Sinus venosus – Embryonic structure that collects blood from veins and directs it into primitive atrium.
• Vitelline veins – Carry nutrient-rich blood from yolk sac to sinus venosus.
• Umbilical veins – Carry oxygenated blood from placenta to sinus venosus.
• Common cardinal veins – Return deoxygenated blood from body to sinus venosus.
• Subcardinal veins – Contribute to formation of inferior vena cava, renal veins, not directly to sinus venosus.
• Sinuatrial node – Pacemaker tissue develops near right sinus venosus.
• Right horn of sinus venosus – Becomes part of right atrium and smooth-walled portion (sinus venarum).
• Left horn of sinus venosus – Forms coronary sinus and oblique vein of left atrium.
• Embryonic veins – Vitelline, umbilical, cardinal, subcardinal, sacrocardinal systems in fetal circulation.
• Clinical relevance – Abnormal venous development causes persistent left superior vena cava or venous anomalies.
Chapter: Embryology
Topic: Cardiovascular System Development
Subtopic: Development of Venous System
Lead Question – 2013
Sinus venosus receives blood from all except?
a) Vitelline vein
b) Umbilical vein
c) Common cardinal vein
d) Subcardinal vein
Explanation: The sinus venosus receives blood from vitelline, umbilical, and common cardinal veins. Subcardinal veins do not directly drain into sinus venosus; they contribute to the formation of the inferior vena cava. Correct answer: Subcardinal vein. Clinically, abnormal venous connections may lead to persistent left superior vena cava or systemic venous anomalies.
Guessed Questions for NEET PG
1) The right horn of sinus venosus contributes to:
a) Right atrium smooth part
b) Left atrium
c) Ventricular septum
d) Pulmonary veins
Explanation: The right horn becomes the smooth-walled portion of the right atrium (sinus venarum). Correct answer: Right atrium smooth part. Clinically, defects here may alter atrial conduction pathways.
2) Left horn of sinus venosus forms:
a) Coronary sinus
b) Inferior vena cava
c) Superior vena cava
d) Right atrial appendage
Explanation: The left horn becomes the coronary sinus and oblique vein of left atrium. Correct answer: Coronary sinus. Abnormal development can result in persistent left superior vena cava.
3) Vitelline veins contribute to:
a) Portal vein
b) Pulmonary veins
c) Subclavian veins
d) Coronary sinus
Explanation: Vitelline veins form portal vein, part of inferior vena cava, and hepatic veins. Correct answer: Portal vein. Clinical: vitelline anomalies can cause portal vein malformations.
4) Umbilical vein develops into:
a) Ligamentum teres hepatis
b) Superior vena cava
c) Subclavian vein
d) Inferior vena cava
Explanation: The left umbilical vein persists and becomes ligamentum teres hepatis after birth. Correct answer: Ligamentum teres hepatis. Clinical: failure of obliteration causes patent umbilical vein in neonates.
5) Common cardinal veins form:
a) Superior vena cava
b) Inferior vena cava
c) Pulmonary vein
d) Coronary sinus
Explanation: Common cardinal veins drain into sinus venosus and contribute to SVC and part of IVC. Correct answer: Superior vena cava. Clinical: anomalies can cause SVC duplication.
6) Subcardinal veins contribute to formation of:
a) Inferior vena cava
b) Superior vena cava
c) Coronary sinus
d) Pulmonary veins
Explanation: Subcardinal veins form the renal segment of IVC and renal veins. Correct answer: Inferior vena cava. Abnormalities may lead to retrocaval ureter.
7) Sacrocardinal veins contribute to:
a) Inferior vena cava lower portion
b) Superior vena cava
c) Pulmonary veins
d) Coronary sinus
Explanation: Sacrocardinal veins form the distal IVC and common iliac veins. Correct answer: Inferior vena cava lower portion. Clinical: anomalies cause double IVC.
8) Sinuatrial node develops near:
a) Right sinus venosus
b) Left atrium
c) Left horn
d) Right ventricle
Explanation: SA node develops near right sinus venosus at junction with primitive atrium. Correct answer: Right sinus venosus. Clinical: congenital arrhythmias can arise from SA node maldevelopment.
9) Persistent left superior vena cava results from:
a) Left common cardinal vein
b) Right cardinal vein
c) Subcardinal vein
d) Vitelline vein
Explanation: Persistent left SVC occurs when left common cardinal vein fails to regress. Correct answer: Left common cardinal vein. Clinically relevant in central line placement and cardiac surgery.
10) Portal vein forms from:
a) Vitelline veins
b) Umbilical veins
c) Subcardinal veins
d) Common cardinal veins
Explanation: Portal vein originates from vitelline veins during embryogenesis. Correct answer: Vitelline veins. Clinical: anomalies lead to portal vein agenesis or malformations, affecting hepatic blood flow.
Keyword Definitions
• Pharyngeal arches – Embryonic structures forming muscles, arteries, cartilage, and nerves of head and neck.
• First arch – Gives muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani, tensor palati.
• Second arch – Muscles of facial expression, stapedius, stylohyoid, posterior belly of digastric.
• Third arch – Gives rise to stylopharyngeus muscle, supplied by glossopharyngeal nerve (CN IX).
• Fourth arch – Cricothyroid, pharyngeal constrictors, soft palate muscles (except tensor palati).
• Sixth arch – Intrinsic laryngeal muscles except cricothyroid.
• Stylopharyngeus – Elevates pharynx during swallowing, only muscle of third arch.
• Cranial nerves – Each arch linked to a nerve: V, VII, IX, X.
• Arch anomalies – Defective arch development causes syndromes (DiGeorge, Treacher Collins).
• Clinical importance – Lesions of CN IX affect gag reflex and swallowing.
Chapter: Embryology
Topic: Pharyngeal Apparatus
Subtopic: Muscular Derivatives of Pharyngeal Arches
Lead Question – 2013
Muscle of third arch?
a) Tensor tympani
b) Stylopharyngeus
c) Cricothyroid
d) None
Explanation: The third arch forms only the stylopharyngeus muscle, innervated by CN IX (glossopharyngeal). Correct answer: Stylopharyngeus. It plays a role in elevating pharynx during swallowing. Lesions impair gag reflex. Tensor tympani (1st arch), cricothyroid (4th arch) are incorrect.
Guessed Questions for NEET PG
1) Muscles of mastication are derived from:
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The first arch produces muscles of mastication along with tensor palati, tensor tympani, mylohyoid. Correct answer: First arch. Clinical: V3 nerve injury causes jaw deviation and chewing weakness.
2) Which arch forms muscles of facial expression?
a) First
b) Second
c) Third
d) Fourth
Explanation: Second arch forms muscles of facial expression and stapedius, supplied by facial nerve (CN VII). Correct answer: Second arch. Clinical: Bell’s palsy causes facial droop due to CN VII dysfunction.
3) Cricothyroid is derived from:
a) Second arch
b) Third arch
c) Fourth arch
d) Sixth arch
Explanation: Cricothyroid belongs to fourth arch derivatives, innervated by external laryngeal branch of vagus. Correct answer: Fourth arch. Injury leads to inability to produce high-pitched sounds.
4) All intrinsic laryngeal muscles except cricothyroid develop from:
a) Fourth arch
b) Sixth arch
c) First arch
d) Second arch
Explanation: The sixth arch gives rise to intrinsic laryngeal muscles (except cricothyroid), supplied by recurrent laryngeal nerve. Correct answer: Sixth arch. Injury results in hoarseness or stridor.
5) Mylohyoid belongs to which arch?
a) First
b) Second
c) Third
d) Fourth
Explanation: The mylohyoid muscle is a derivative of the first arch, innervated by mandibular nerve (V3). Correct answer: First arch. Weakness causes impaired swallowing and tongue movements.
6) A patient with glossopharyngeal nerve lesion will show paralysis of:
a) Stylopharyngeus
b) Cricothyroid
c) Buccinator
d) Mylohyoid
Explanation: Glossopharyngeal nerve supplies stylopharyngeus (third arch). Correct answer: Stylopharyngeus. Clinical finding: absent gag reflex and swallowing difficulty.
7) Stapedius arises from which arch?
a) First
b) Second
c) Third
d) Fourth
Explanation: The stapedius is a derivative of the second arch, supplied by facial nerve. Correct answer: Second arch. Injury causes hyperacusis due to loss of dampening of sound vibrations.
8) Which muscle is supplied by mandibular nerve but not part of mastication?
a) Tensor tympani
b) Masseter
c) Temporalis
d) Medial pterygoid
Explanation: Tensor tympani, a first arch derivative, is innervated by mandibular nerve but not a muscle of mastication. Correct answer: Tensor tympani. Dysfunction causes abnormal sound sensitivity.
9) Pharyngeal constrictors are derived from:
a) First arch
b) Third arch
c) Fourth arch
d) Sixth arch
Explanation: The pharyngeal constrictors come from the fourth arch, supplied by pharyngeal branches of vagus. Correct answer: Fourth arch. Dysfunction produces dysphagia and aspiration risk.
10) Neonatal stridor due to recurrent laryngeal nerve injury involves muscles from:
a) Fourth arch
b) Sixth arch
c) Second arch
d) Third arch
Explanation: Sixth arch gives intrinsic laryngeal muscles except cricothyroid. Correct answer: Sixth arch. Recurrent laryngeal palsy causes hoarseness and airway compromise post-thyroid surgery.
Keyword Definitions
• Aortic arches – Embryonic vascular structures connecting the truncus arteriosus with the dorsal aortae.
• Arch of aorta – Major systemic artery arch formed mainly from the left 4th aortic arch.
• Dorsal aorta – Paired embryonic vessels that later fuse to form the descending aorta.
• Truncus arteriosus – Primitive outflow tract of the heart, later forming the aorta and pulmonary artery.
• Right subclavian artery – Derived from right 4th arch and part of dorsal aorta.
• Left common carotid – Derived from the left 3rd arch.
• Pulmonary arteries – Derived from the 6th aortic arch.
• Patent ductus arteriosus – Persistence of the distal left 6th arch, connecting aorta and pulmonary artery.
• Double aortic arch – Vascular ring anomaly due to persistence of both 4th arches.
• Coarctation of aorta – Congenital narrowing of the aortic lumen, often at ductus arteriosus site.
• Interrupted aortic arch – Rare defect due to abnormal regression of 4th aortic arch.
Chapter: Embryology
Topic: Cardiovascular System Development
Subtopic: Development of Aortic Arches
Lead Question – 2013
Arch of Aorta develops from which aortic arch artery?
a) Right Pt
b) Right 3rd
c) Left 4th
d) Left 3rd
Explanation: The arch of the aorta is derived primarily from the left 4th aortic arch. This embryonic vessel contributes to the definitive systemic circulation. Correct answer: Left 4th arch. Clinically, abnormal development may result in anomalies like double aortic arch or interrupted aortic arch, causing airway/esophageal compression.
Guessed Questions for NEET PG
1) The right subclavian artery is derived from:
a) Right 3rd arch
b) Right 4th arch
c) Left 4th arch
d) Right 6th arch
Explanation: The right subclavian artery forms from the right 4th aortic arch and a part of the right dorsal aorta. Correct answer: Right 4th arch. Clinical note: abnormal regression may cause aberrant right subclavian artery, compressing the esophagus (dysphagia lusoria).
2) The common carotid artery is derived from:
a) 1st arch
b) 2nd arch
c) 3rd arch
d) 4th arch
Explanation: Both right and left common carotid arteries develop from the 3rd aortic arches. Correct answer: 3rd arch. Clinical note: anomalies can alter carotid bifurcation, relevant in vascular surgery.
3) Pulmonary arteries develop from:
a) 4th arch
b) 6th arch
c) 2nd arch
d) Dorsal aorta only
Explanation: The proximal part of the 6th aortic arches form the proximal pulmonary arteries. Correct answer: 6th arch. Clinical: persistence of distal left 6th arch forms patent ductus arteriosus (PDA).
4) Which arch gives rise to maxillary artery?
a) 1st arch
b) 2nd arch
c) 3rd arch
d) 4th arch
Explanation: The 1st aortic arch largely disappears, but remnants contribute to the maxillary artery. Correct answer: 1st arch. Clinical relevance: early vascular anomalies in the head and neck may involve this origin.
5) Stapedial artery arises from which arch?
a) 1st arch
b) 2nd arch
c) 3rd arch
d) 4th arch
Explanation: The stapedial artery develops from the 2nd arch artery, though it regresses later. Correct answer: 2nd arch. Persistent stapedial artery may cause conductive hearing loss.
6) The ductus arteriosus develops from:
a) Right 4th arch
b) Left 6th arch
c) Right 6th arch
d) Left 3rd arch
Explanation: The ductus arteriosus, an essential fetal shunt, originates from the distal part of the left 6th arch. Correct answer: Left 6th arch. Clinical: persistence after birth leads to PDA, causing left-to-right shunt.
7) Double aortic arch is due to persistence of:
a) Right 6th arch
b) Both 4th arches
c) Left 3rd arch
d) Right 2nd arch
Explanation: Failure of regression of the right 4th arch alongside the left 4th arch causes double aortic arch. Correct answer: Both 4th arches. Clinically, this creates a vascular ring compressing trachea and esophagus.
8) The external carotid artery develops from:
a) Ventral part of 3rd arch
b) Ventral part of 1st arch
c) Dorsal part of 2nd arch
d) Dorsal aorta
Explanation: The external carotid artery arises as a branch from the ventral part of the 3rd arch. Correct answer: Ventral part of 3rd arch. Clinical note: variations important in carotid endarterectomy.
9) Interrupted aortic arch type B is due to regression of:
a) Left 3rd arch
b) Left 4th arch
c) Left 6th arch
d) Right 4th arch
Explanation: In type B interrupted aortic arch, the defect is due to abnormal regression of the left 4th arch. Correct answer: Left 4th arch. Clinical: presents with severe neonatal heart failure.
10) The vertebral arteries are derived from:
a) Intersegmental arteries
b) 3rd arch
c) 4th arch
d) 6th arch
Explanation: The vertebral arteries are formed by longitudinal anastomosis of cervical intersegmental arteries, not aortic arches. Correct answer: Intersegmental arteries. Clinical: anomalies may contribute to vertebrobasilar insufficiency syndromes.
Keyword Definitions
• Retina – Light-sensitive tissue lining the back of the eye, derived from neuroectoderm.
• Optic vesicle – Outgrowth from the diencephalon that develops into the retina.
• Neuroectoderm – Embryonic tissue forming nervous system structures, including retina.
• Diencephalon – Part of the forebrain giving rise to retina, thalamus, and hypothalamus.
• Mesencephalon – Midbrain, involved in visual and auditory pathways.
• Telencephalon – Forebrain region developing into cerebral hemispheres.
• Optic cup – Double-layered structure from optic vesicle forming neural and pigmented retina.
• Lens placode – Surface ectoderm thickening forming the lens.
• Choroid fissure – Temporary groove in optic cup for hyaloid artery entry.
• Coloboma – Defect due to failure of choroid fissure closure.
• Retinoblastoma – Malignant retinal tumor from embryonic retinal cells.
Chapter: Embryology
Topic: Nervous System Development
Subtopic: Development of Eye
Lead Question – 2013
The retina is an outgrowth of the?
a) Mesencephalon
b) Diencephalon
c) Telencephalon
d) Pons
Explanation: The retina originates from the optic vesicle, which is a direct outgrowth of the diencephalon. This neuroectodermal origin distinguishes it from mesodermal or surface ectodermal derivatives. Correct answer: Diencephalon. Clinical relevance: optic nerve hypoplasia results from defective diencephalic outgrowth.
Guessed Questions for NEET PG
1) The optic nerve develops from:
a) Mesoderm
b) Diencephalon
c) Optic stalk
d) Surface ectoderm
Explanation: The optic nerve develops from the optic stalk, which connects the optic vesicle to the brain. Correct answer: Optic stalk. Clinically, optic nerve coloboma occurs if the choroid fissure fails to close.
2) The lens of the eye develops from:
a) Surface ectoderm
b) Neural crest
c) Diencephalon
d) Mesoderm
Explanation: The lens is derived from surface ectoderm as the lens placode, induced by the optic vesicle. Correct answer: Surface ectoderm. Clinical note: congenital cataract results from abnormal lens development.
3) Pigmented layer of retina develops from:
a) Surface ectoderm
b) Inner layer of optic cup
c) Outer layer of optic cup
d) Neural crest cells
Explanation: The outer layer of the optic cup forms the retinal pigmented epithelium. Correct answer: Outer layer of optic cup. Defects may cause albinism due to melanin pathway abnormalities.
4) Failure of choroid fissure closure leads to:
a) Retinoblastoma
b) Coloboma
c) Cataract
d) Aniridia
Explanation: Incomplete closure of the choroid fissure results in a coloboma, seen as a keyhole defect in the iris or retina. Correct answer: Coloboma.
5) Corneal endothelium and stroma are derived from:
a) Neural crest cells
b) Surface ectoderm
c) Diencephalon
d) Mesoderm only
Explanation: Neural crest cells migrate to form corneal stroma and endothelium. Correct answer: Neural crest cells. Clinical note: abnormal migration causes congenital corneal opacities.
6) Which of the following is a neuroectodermal derivative?
a) Lens
b) Retina
c) Corneal epithelium
d) Conjunctiva
Explanation: The retina arises from neuroectoderm, specifically the diencephalic optic vesicle. Correct answer: Retina. Clinical relevance: retinoblastoma arises from retinal neuroectodermal cells.
7) The ciliary body muscles are derived from:
a) Neuroectoderm
b) Neural crest
c) Surface ectoderm
d) Mesoderm
Explanation: Ciliary body muscles are unusual because they are neuroectodermal in origin, unlike most smooth muscles. Correct answer: Neuroectoderm. Clinical note: dysfunction leads to impaired accommodation.
8) Aniridia results from mutation in:
a) PAX6 gene
b) PAX2 gene
c) SHH gene
d) RET gene
Explanation: PAX6 is the master gene for eye development. Its mutation causes aniridia, characterized by absence of iris. Correct answer: PAX6 gene.
9) Persistent hyaloid artery may cause:
a) Cataract
b) Coloboma
c) Aniridia
d) Retinitis pigmentosa
Explanation: If the embryonic hyaloid artery fails to regress, it leads to persistent fetal vasculature causing cataract. Correct answer: Cataract.
10) Which part of the brain gives rise to the pineal gland and retina both?
a) Mesencephalon
b) Diencephalon
c) Telencephalon
d) Myelencephalon
Explanation: Both pineal gland and retina originate from the diencephalon, showing its key role in sensory organ development. Correct answer: Diencephalon.
Keyword Definitions
• Heart tube – Primitive structure that gives rise to the adult heart.
• Cardiac jelly – Gelatinous connective tissue surrounding the early heart tube, aiding septation and valve formation.
• Mesocardium – Mesodermal tissue suspending the developing heart tube.
• Myocardium – Muscular layer of the heart derived from splanchnic mesoderm.
• Endocardium – Inner endothelial lining of the heart tube.
• Pericardium – Fibroserous sac enclosing the heart.
• Endocardial cushions – Thickenings in cardiac jelly that contribute to septa and valves.
• Septation – Partitioning process forming atria, ventricles, and outflow tracts.
• Splanchnic mesoderm – Embryonic layer giving rise to myocardium and epicardium.
• Conotruncal ridges – Structures contributing to aorticopulmonary septum.
• Congenital heart disease – Malformations due to abnormal heart tube development.
Chapter: Embryology
Topic: Cardiovascular Development
Subtopic: Development of Heart Tube
Lead Question – 2013
Jelly formed around the heart tube during early development, contributes to the formation of:
a) Pericardium
b) Mesocardium
c) Myocardium
d) Endocardium
Explanation: The jelly around the early heart tube is known as cardiac jelly. It plays a crucial role in septation and valve formation. It contributes to the development of the endocardial cushions, which later form septa and valves. Correct answer: Endocardium. Clinical relevance: abnormal cushions cause atrioventricular septal defects.
Guessed Questions for NEET PG
1) The myocardium of the heart develops from:
a) Neural crest cells
b) Splanchnic mesoderm
c) Cardiac jelly
d) Endocardial cushions
Explanation: The myocardium develops from the splanchnic mesoderm surrounding the heart tube. Neural crest cells contribute to outflow tract formation. Correct answer: Splanchnic mesoderm. Clinically, failure of proper myocardial compaction leads to non-compaction cardiomyopathy.
2) Endocardial cushions are primarily derived from:
a) Cardiac jelly
b) Neural crest
c) Paraxial mesoderm
d) Somites
Explanation: Endocardial cushions arise from cardiac jelly with contribution from neural crest cells. They form atrial and ventricular septa, as well as atrioventricular valves. Correct answer: Cardiac jelly. Maldevelopment causes atrioventricular septal defects.
3) The epicardium of the heart develops from:
a) Neural crest
b) Splanchnic mesoderm (proepicardial organ)
c) Cardiac jelly
d) Endocardium
Explanation: The epicardium arises from mesothelial cells of the proepicardial organ derived from splanchnic mesoderm. Correct answer: Splanchnic mesoderm. Epicardial defects can impair coronary vessel development.
4) Which embryological structure gives rise to the sinoatrial node?
a) Sinus venosus
b) Endocardial cushion
c) Cardiac jelly
d) Conotruncal ridge
Explanation: The sinoatrial node develops from the sinus venosus and atrial wall junction. Correct answer: Sinus venosus. Clinical importance: abnormalities cause arrhythmias and conduction defects.
5) Cardiac looping establishes which relation of ventricles?
a) Left ventricle anterior, right ventricle posterior
b) Right ventricle anterior, left ventricle posterior
c) Both anterior
d) Both posterior
Explanation: During cardiac looping, the primitive ventricle moves left and inferior, right ventricle moves anteriorly. Correct answer: Right ventricle anterior, left ventricle posterior. Abnormal looping causes congenital malpositions.
6) Failure of endocardial cushion fusion results in:
a) Tetralogy of Fallot
b) Transposition of great arteries
c) Atrioventricular septal defect
d) Patent ductus arteriosus
Explanation: Endocardial cushions are essential for atrioventricular septation. Their failure causes AV septal defect. Correct answer: Atrioventricular septal defect. Seen in Down syndrome.
7) Neural crest cells contribute to formation of:
a) Interventricular septum muscular part
b) Aorticopulmonary septum
c) Endocardial cushions
d) Cardiac jelly
Explanation: Neural crest cells form the aorticopulmonary septum, which separates aorta and pulmonary trunk. Correct answer: Aorticopulmonary septum. Defects cause persistent truncus arteriosus and conotruncal anomalies.
8) Which embryological structure forms the coronary arteries?
a) Endocardial cushions
b) Proepicardial organ
c) Cardiac jelly
d) Sinus venosus
Explanation: Coronary vessels develop from mesenchymal cells of the proepicardial organ. Correct answer: Proepicardial organ. Defects cause coronary artery anomalies leading to ischemia.
9) Which part of the heart develops last embryologically?
a) Left atrium
b) Right atrium
c) Ventricles
d) Outflow tracts
Explanation: Outflow tracts are the last structures to complete development with neural crest contribution. Correct answer: Outflow tracts. Defects cause conotruncal malformations like transposition of great arteries.
10) Abnormality of cardiac jelly primarily affects formation of:
a) Pericardium
b) Myocardium
c) Valves and septa
d) Coronary arteries
Explanation: Cardiac jelly is key in valve and septum development. Defects in its formation or migration result in septal defects. Correct answer: Valves and septa.
Keyword Definitions
• Inferior vena cava (IVC) – Main vein returning deoxygenated blood from lower body to heart.
• Cardinal veins – Primitive venous system of embryo including anterior, posterior, common cardinal veins.
• Subcardinal veins – Embryonic veins contributing to renal, gonadal, and IVC formation.
• Supracardinal veins – Embryonic veins forming azygos, hemiazygos, and part of IVC.
• Sacrocardinal veins – Veins draining lower limbs, contribute to distal IVC.
• Anastomosis – Connection between vessels ensuring proper venous return.
• Venous anomalies – Variations due to abnormal regression or persistence of embryonic veins.
• Double IVC – Persistence of bilateral supracardinal or subcardinal channels resulting in two IVCs.
• Left IVC – Occurs when left supracardinal persists instead of regressing.
• Retroaortic renal vein – Venous anomaly from altered regression of subcardinal/supracardinal veins.
• Clinical relevance – Important for imaging, renal surgery, and catheter placement.
Chapter: Embryology
Topic: Development of Venous System
Subtopic: Inferior Vena Cava and Variants
Lead Question - 2013
Double inferior vena cava is formed due to?
a) Persistence of sacrocardinal veins
b) Persistence of supracardinal veins
c) Persistence of subcardinal veins
d) Persistence of both supracardinal and subcardinal veins
Explanation: A double inferior vena cava results when both right and left supracardinal veins persist instead of regression. This anomaly is clinically significant in radiology and surgical planning. Correct answer: Persistence of supracardinal veins. It may mimic lymphadenopathy or retroperitoneal mass on imaging.
Question 2
Which embryonic vein forms the hepatic segment of the inferior vena cava?
a) Right vitelline vein
b) Left vitelline vein
c) Subcardinal vein
d) Supracardinal vein
Explanation: The hepatic segment of the IVC develops from the right vitelline vein, which contributes to liver sinusoids and portal vein. Correct answer: Right vitelline vein. Defects may present as interrupted IVC with azygos continuation.
Question 3
The renal segment of the IVC is formed by?
a) Subcardinal vein
b) Supracardinal vein
c) Sacrocardinal vein
d) Vitelline vein
Explanation: The renal segment of IVC is formed from subcardinal veins and their anastomosis with supracardinal veins. Correct answer: Subcardinal vein. Developmental errors can cause retroaortic left renal vein anomaly.
Question 4
Which embryonic structure gives rise to the azygos and hemiazygos veins?
a) Subcardinal veins
b) Supracardinal veins
c) Vitelline veins
d) Sacrocardinal veins
Explanation: The azygos and hemiazygos veins develop from supracardinal veins. Correct answer: Supracardinal veins. These provide alternate pathways for venous return in IVC obstruction.
Question 5
A retroaortic left renal vein develops due to abnormal persistence of?
a) Dorsal arch of subcardinal–supracardinal anastomosis
b) Ventral arch of subcardinal–supracardinal anastomosis
c) Sacrocardinal venous loop
d) Left vitelline venous loop
Explanation: Retroaortic left renal vein arises from persistence of dorsal limb of subcardinal–supracardinal anastomosis. Correct answer: Dorsal arch of subcardinal–supracardinal anastomosis. It has clinical implications during renal transplantation and surgery.
Question 6
Which part of the IVC is derived from the sacrocardinal veins?
a) Suprarenal segment
b) Renal segment
c) Hepatic segment
d) Postrenal segment
Explanation: Sacrocardinal veins contribute to the postrenal segment of the IVC, responsible for draining lower limbs. Correct answer: Postrenal segment. Persistence of abnormal channels here can cause double IVC.
Question 7
A left-sided inferior vena cava develops from persistence of?
a) Left supracardinal vein
b) Left subcardinal vein
c) Left sacrocardinal vein
d) Left vitelline vein
Explanation: Persistence of left supracardinal vein causes a left-sided IVC. Correct answer: Left supracardinal vein. It may complicate retroperitoneal surgery and is important in radiological diagnosis.
Question 8
Which clinical condition is associated with azygos continuation of IVC?
a) Persistence of left vitelline vein
b) Absence of hepatic segment of IVC
c) Absence of sacrocardinal segment
d) Failure of renal anastomosis
Explanation: Azygos continuation occurs when hepatic segment of IVC is absent, blood drains through azygos vein. Correct answer: Absence of hepatic segment of IVC. This anomaly is often detected incidentally on imaging.
Question 9
Which embryonic vein mainly contributes to gonadal veins?
a) Subcardinal vein
b) Supracardinal vein
c) Vitelline vein
d) Sacrocardinal vein
Explanation: Gonadal veins develop from subcardinal veins. Correct answer: Subcardinal vein. Left gonadal vein drains into left renal vein, while right drains directly into IVC, explaining asymmetry in varicocele prevalence.
Question 10
Which anomaly results from persistence of both supracardinal veins?
a) Double IVC
b) Left renal vein anomaly
c) Retroaortic renal vein
d) Interrupted IVC
Explanation: Double IVC arises when both right and left supracardinal veins persist. Correct answer: Double IVC. Clinically, it is important in IVC filter placement and radiology to avoid misdiagnosis as a pathological mass.
Question 11
Interrupted IVC with azygos continuation is most associated with which syndrome?
a) Down syndrome
b) Turner syndrome
c) Polysplenia syndrome
d) Patau syndrome
Explanation: Interrupted IVC with azygos continuation is a classic feature of polysplenia syndrome, a heterotaxy disorder. Correct answer: Polysplenia syndrome. Awareness is crucial during cardiac and abdominal imaging to prevent misinterpretation.
Keyword Definitions
• Somites – Paired blocks of paraxial mesoderm forming vertebrae, ribs, skeletal muscle, dermis.
• Paraxial mesoderm – Mesodermal tissue flanking the neural tube forming somites.
• Cervical somites – First somites to appear, giving rise to occipital and cervical structures.
• Thoracic somites – Form thoracic vertebrae, ribs, and associated muscles.
• Lumbar somites – Form lumbar vertebrae and trunk musculature.
• Sacral somites – Contribute to sacrum and pelvic structures.
• Dermatome – Somite portion forming dermis.
• Myotome – Somite portion forming skeletal muscles.
• Sclerotome – Somite portion forming vertebrae and ribs.
• Somitogenesis – Sequential formation of somites in cranio-caudal direction.
• Neural crest – Migrating cells associated with somite development.
Chapter: Embryology
Topic: Development of Musculoskeletal System
Subtopic: Somite Formation
Lead Question
Which level do somites initially form?
a) Thoracic level
b) Cervical level
c) Lumbar level
d) Sacral level
Explanation: Somites appear first in the cervical region around day 20 of development, and then proceed sequentially in a cranio-caudal direction. They differentiate into dermatome, myotome, and sclerotome. Correct answer: Cervical level. Clinical correlation: abnormal somitogenesis can cause congenital vertebral anomalies like scoliosis.
Question 2
At which day of embryonic development do the first somites appear?
a) Day 10
b) Day 15
c) Day 20
d) Day 25
Explanation: The first somites appear around day 20 of development in the cervical region. This marks the beginning of segmentation in the embryo. Correct answer: Day 20.
Question 3
How many pairs of somites are typically formed in humans?
a) 31
b) 33
c) 42-44
d) 28
Explanation: Humans develop about 42–44 pairs of somites, though some regress, leaving 31 pairs of spinal nerves. Correct answer: 42-44 pairs. Somite count is a reliable indicator of embryonic age.
Question 4
Which portion of a somite forms the vertebrae and ribs?
a) Dermatome
b) Myotome
c) Sclerotome
d) Neural crest
Explanation: The sclerotome differentiates into vertebrae and ribs. Myotome forms skeletal muscles, while dermatome forms dermis of skin. Correct answer: Sclerotome.
Question 5
Which somites contribute to the formation of limb muscles?
a) Cervical and thoracic
b) Lumbar and sacral
c) Thoracic and lumbar
d) Cervical and lumbar
Explanation: Limb muscles develop from myotomes of cervical and lumbar somites that migrate into limb buds. Correct answer: Cervical and lumbar. Defective migration may cause limb musculature anomalies.
Question 6
Dermatome cells derived from somites form which structure?
a) Epidermis
b) Dermis of skin
c) Cartilage
d) Skeletal muscle
Explanation: The dermatome portion of somites differentiates into dermis of the skin. Correct answer: Dermis of skin. This explains segmental dermatomal distribution of cutaneous nerves.
Question 7
The occipital somites contribute to which skeletal structures?
a) Mandible
b) Skull base and tongue muscles
c) Scapula
d) Sternum
Explanation: Occipital somites contribute to skull base bones and intrinsic tongue muscles. Correct answer: Skull base and tongue muscles. Their development is clinically significant in congenital craniovertebral anomalies.
Question 8
Failure of somite segmentation results in?
a) Scoliosis
b) Klippel-Feil syndrome
c) Spina bifida
d) Sirenomelia
Explanation: Failure of segmentation of cervical somites results in fused cervical vertebrae, seen in Klippel-Feil syndrome. Correct answer: Klippel-Feil syndrome. It presents with short neck, low hairline, and limited mobility.
Question 9
Which signaling pathway is crucial for somite formation?
a) Notch signaling
b) Hedgehog signaling
c) Wnt signaling
d) VEGF signaling
Explanation: Notch signaling plays a critical role in regulating segmentation and somitogenesis. Correct answer: Notch signaling. Its disruption can lead to congenital vertebral malformations.
Question 10
In congenital scoliosis, abnormal development of which somite derivative is implicated?
a) Dermatome
b) Myotome
c) Sclerotome
d) Neural crest
Explanation: Congenital scoliosis occurs due to defective vertebral formation from sclerotome. Correct answer: Sclerotome. Hemivertebrae or block vertebrae may cause lateral spinal curvature.
Question 11
Which clinical condition is associated with defective migration of hypoglossal nerve-related somites?
a) Micrognathia
b) Ankyloglossia
c) Tongue muscular hypoplasia
d) Cleft palate
Explanation: Defective migration of occipital somites, which form tongue muscles, can cause tongue muscular hypoplasia. Correct answer: Tongue muscular hypoplasia. It may impair swallowing and speech in infants.
Keyword Definitions
• Pronephros – The earliest, rudimentary kidney structure, nonfunctional in humans.
• Mesonephros – The second temporary kidney, functions briefly during embryogenesis.
• Metanephros – The permanent kidney that develops during the 5th week of gestation.
• Ureteric bud – Outgrowth of mesonephric duct forming collecting system of kidney.
• Metanephric blastema – Mesenchymal tissue forming nephrons of the kidney.
• Nephron – Functional unit of kidney, includes glomerulus, tubules, loop of Henle.
• Collecting ducts – Structures draining urine from nephrons to renal pelvis.
• Oligohydramnios – Low amniotic fluid due to defective fetal renal function.
• Potter sequence – Clinical syndrome from renal agenesis causing oligohydramnios and limb deformities.
• Wilm’s tumor – Pediatric renal tumor derived from metanephric blastema.
• Polycystic kidney disease – Inherited disorder with cystic dilation of nephrons and collecting ducts.
Chapter: Embryology
Topic: Development of the Urinary System
Subtopic: Kidney Development
Lead Question - 2013
Collecting part of kidney develops from?
a) Pronephros
b) Mesonephros
c) Metanephros
d) Ureteric bud
Explanation: The collecting system of the kidney, including collecting ducts, calyces, pelvis, and ureter, develops from the ureteric bud. Nephrons arise from the metanephric blastema. Correct answer: Ureteric bud. Clinical correlation: failure of ureteric bud-metanephric interaction causes renal agenesis and Potter sequence.
Question 2
Which embryonic structure gives rise to the nephron?
a) Ureteric bud
b) Metanephric blastema
c) Mesonephric duct
d) Cloaca
Explanation: Nephrons including glomerulus, proximal tubule, loop of Henle, and distal tubule originate from the metanephric blastema. Correct answer: Metanephric blastema. Wilm’s tumor arises from abnormal proliferation of blastemal tissue.
Question 3
Failure of ureteric bud to develop results in?
a) Multicystic dysplastic kidney
b) Renal agenesis
c) Horseshoe kidney
d) Polycystic kidney disease
Explanation: If ureteric bud fails to form, the collecting system and kidney do not develop, leading to renal agenesis. Correct answer: Renal agenesis. Bilateral cases cause Potter sequence with pulmonary hypoplasia.
Question 4
Which structure forms the ureter?
a) Metanephric blastema
b) Ureteric bud
c) Mesonephros
d) Cloacal membrane
Explanation: The ureter, renal pelvis, calyces, and collecting ducts are derived from the ureteric bud. Correct answer: Ureteric bud. Anomalies may cause duplicated ureters or obstructive uropathy.
Question 5
A newborn with Potter sequence most likely had failure of?
a) Mesonephric duct development
b) Ureteric bud induction of metanephric blastema
c) Pronephros degeneration
d) Cloacal partitioning
Explanation: Potter sequence arises due to oligohydramnios from bilateral renal agenesis. This occurs when ureteric bud fails to induce metanephric blastema. Correct answer: Ureteric bud induction failure.
Question 6
Which week does the permanent kidney (metanephros) begin to develop?
a) 3rd
b) 4th
c) 5th
d) 8th
Explanation: Metanephros, the permanent kidney, begins development in the 5th week of gestation and becomes functional by the 10th week. Correct answer: 5th week.
Question 7
Multicystic dysplastic kidney results from abnormal interaction between?
a) Cloaca and allantois
b) Metanephric blastema and ureteric bud
c) Mesonephric duct and pronephros
d) Nephron and somites
Explanation: Multicystic dysplastic kidney occurs due to defective interaction between ureteric bud and metanephric blastema. Correct answer: Metanephric blastema and ureteric bud.
Question 8
Which structure contributes to formation of efferent arteriole of glomerulus?
a) Metanephric blastema
b) Ureteric bud
c) Mesonephric duct
d) Dorsal aorta branches
Explanation: Renal vasculature including afferent and efferent arterioles develops from branches of dorsal aorta. Correct answer: Dorsal aorta branches. This ensures blood supply to developing glomeruli.
Question 9
In horseshoe kidney, fusion occurs at which pole?
a) Upper pole
b) Lower pole
c) Mid pole
d) Both poles
Explanation: In horseshoe kidney, the lower poles fuse, preventing ascent due to inferior mesenteric artery obstruction. Correct answer: Lower pole. It may predispose to obstruction, stones, or infection.
Question 10
Polycystic kidney disease is associated with defective development of?
a) Collecting ducts
b) Proximal tubules
c) Loop of Henle
d) Renal pelvis
Explanation: Polycystic kidney disease involves abnormal development of nephrons and collecting ducts, leading to multiple fluid-filled cysts. Correct answer: Collecting ducts. It can cause hypertension and renal failure.
Question 11
A child presents with a duplicated ureter. This anomaly is due to?
a) Early splitting of ureteric bud
b) Failure of mesonephros regression
c) Persistence of pronephros
d) Cloacal membrane defect
Explanation: Duplicated ureter results from premature bifurcation of the ureteric bud before penetrating the metanephric blastema. Correct answer: Early splitting of ureteric bud. Clinically, it may predispose to reflux or obstruction.
Keyword Definitions
• Neural tube – Embryonic precursor of brain and spinal cord.
• Neural crest cells – Cells giving rise to peripheral nervous system and craniofacial structures.
• Somites – Mesodermal blocks forming vertebrae and skeletal muscles.
• Myelination – Process of forming myelin sheath around axons for faster conduction.
• Prosencephalon – Forebrain region forming cerebrum and diencephalon.
• Mesencephalon – Midbrain responsible for vision and auditory reflexes.
• Rhombencephalon – Hindbrain forming pons, medulla, and cerebellum.
• Central canal – Cavity of neural tube forming spinal cord canal.
• White matter – Myelinated axonal tracts in CNS.
• Grey matter – Neuronal cell bodies in CNS.
• Spina bifida – Neural tube closure defect affecting vertebral arches.
Chapter: Embryology
Topic: Development of Nervous System
Subtopic: Spinal Cord Development
Lead Question - 2013
Spinal cord develops from?
a) Neural tube
b) Mesencephalon
c) Rhombencephalon
d) Prosencephalon
Explanation: The spinal cord originates from the caudal portion of the neural tube during neurulation. Brain regions like mesencephalon, rhombencephalon, and prosencephalon develop into higher centers, not the spinal cord. Correct answer: Neural tube. Clinical relevance includes spina bifida, a defect from improper neural tube closure.
Question 2
Which cells form the dorsal root ganglia during spinal cord development?
a) Ectodermal placodes
b) Neural crest cells
c) Mesodermal somites
d) Endodermal cells
Explanation: Dorsal root ganglia arise from neural crest cells, which migrate bilaterally from the neural tube. They form sensory neurons, Schwann cells, and sympathetic ganglia. Correct answer: Neural crest cells. Defects may result in peripheral neuropathies or autonomic dysfunctions.
Question 3
The central canal of the spinal cord is derived from which embryonic structure?
a) Notochord
b) Somites
c) Lumen of neural tube
d) Amniotic cavity
Explanation: The central canal forms from the lumen of the neural tube. This canal remains continuous with the ventricular system of the brain. Correct answer: Lumen of neural tube. Its abnormal dilatation can lead to syringomyelia, presenting with dissociated sensory loss.
Question 4
Which glial cells are responsible for myelination in the spinal cord?
a) Schwann cells
b) Astrocytes
c) Oligodendrocytes
d) Microglia
Explanation: In the CNS, including the spinal cord, myelination is carried out by oligodendrocytes. Schwann cells perform the same role in the peripheral nervous system. Correct answer: Oligodendrocytes. Demyelinating disorders like multiple sclerosis highlight the importance of these cells.
Question 5
The motor neurons of the spinal cord develop from which plate of the neural tube?
a) Alar plate
b) Basal plate
c) Roof plate
d) Floor plate
Explanation: Motor neurons of the anterior horn arise from the basal plate of the neural tube. The alar plate gives rise to sensory neurons. Correct answer: Basal plate. Damage leads to motor weakness, as seen in anterior horn cell diseases like poliomyelitis.
Question 6
Which vitamin deficiency is strongly linked with neural tube defects like spina bifida?
a) Vitamin B12
b) Folic acid
c) Vitamin D
d) Vitamin C
Explanation: Maternal folic acid deficiency is a major risk factor for neural tube defects including spina bifida and anencephaly. Correct answer: Folic acid. Supplementation during preconception and early pregnancy prevents these anomalies effectively.
Question 7
In syringomyelia, which part of the spinal cord is commonly affected?
a) Dorsal horn
b) Anterior horn
c) Central canal region
d) White matter tracts
Explanation: Syringomyelia involves cystic dilatation of the central canal of the spinal cord, often at the cervical region. Correct answer: Central canal region. Clinically, it produces cape-like loss of pain and temperature sensation while sparing touch and vibration.
Question 8
Which primary brain vesicle is continuous with the neural tube cranially during development?
a) Mesencephalon
b) Prosencephalon
c) Rhombencephalon
d) All of the above
Explanation: All three primary brain vesicles—prosencephalon, mesencephalon, and rhombencephalon—are continuous cranially with the neural tube, forming higher brain regions. Correct answer: All of the above. This shows the continuity of CNS development from neural tube.
Question 9
Which clinical condition results from failure of the neural tube to close at the cranial end?
a) Spina bifida occulta
b) Syringomyelia
c) Anencephaly
d) Meningomyelocele
Explanation: Failure of the neural tube to close at the cranial neuropore results in anencephaly, a lethal anomaly characterized by absence of cranial vault and brain tissue. Correct answer: Anencephaly.
Question 10
Which part of the neural tube gives rise to sensory neurons of the spinal cord?
a) Basal plate
b) Alar plate
c) Roof plate
d) Floor plate
Explanation: Sensory neurons of the dorsal horn arise from the alar plate of the neural tube. Correct answer: Alar plate. This structural differentiation explains the anatomical segregation of motor and sensory pathways in the spinal cord.
Question 11
A newborn with meningomyelocele most likely has defective development of which structure?
a) Mesodermal somites
b) Neural tube
c) Notochord
d) Amnion
Explanation: Meningomyelocele results from defective closure of the caudal neural tube, leading to herniation of meninges and spinal cord contents. Correct answer: Neural tube. It is associated with neurological deficits and requires early surgical intervention.
Keyword Definitions
• Pharyngeal arches – Embryonic structures forming head and neck components.
• Muscles of mastication – Muscles responsible for chewing, derived from 1st arch.
• Facial nerve – 7th cranial nerve, supplies muscles of facial expression.
• Stylopharyngeus – A muscle derived from 3rd pharyngeal arch.
• Recurrent laryngeal nerve – Branch of vagus nerve supplying intrinsic laryngeal muscles.
• Cranial nerves – Nerves emerging from brainstem supplying head, neck, thorax.
• Branchial apparatus – Collective term for arches, pouches, grooves, membranes.
• Palatine tonsil – Lymphoid tissue derived from 2nd pharyngeal pouch.
• Cleft palate – Developmental defect from failed fusion of palatal shelves.
• Treacher Collins syndrome – 1st arch developmental disorder with craniofacial anomalies.
• DiGeorge syndrome – Disorder from 3rd & 4th pouch failure, thymic hypoplasia.
Chapter: Embryology
Topic: Pharyngeal Apparatus
Subtopic: Pharyngeal Arches and Derivatives
Lead Question - 2013
Pharyngeal muscles are derived from which pharyngeal arch?
a) 1st
b) 2nd
c) 3rd
d) 5th
Explanation: The pharyngeal constrictor muscles originate from the 4th and 6th pharyngeal arches, supplied by branches of vagus nerve. Options provided omit the correct arches, but clinically, these muscles develop from the 4th and 6th arches. Correct interpretation emphasizes the vagus nerve contribution and arch differentiation.
Question 2
Which muscle is derived from the 1st pharyngeal arch?
a) Stylopharyngeus
b) Masseter
c) Buccinator
d) Cricothyroid
Explanation: The first pharyngeal arch gives rise to muscles of mastication, including masseter, temporalis, and pterygoids, supplied by mandibular nerve. Stylopharyngeus derives from 3rd arch, buccinator from 2nd, and cricothyroid from 4th. Correct answer: Masseter.
Question 3
The facial nerve supplies muscles originating from which arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: The second pharyngeal arch forms muscles of facial expression, stapedius, stylohyoid, and posterior belly of digastric, all supplied by facial nerve (cranial nerve VII). Correct answer: 2nd arch.
Question 4
Stylopharyngeus muscle is derived from which arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: Stylopharyngeus originates from the 3rd pharyngeal arch and is supplied by glossopharyngeal nerve (cranial nerve IX). This muscle plays a role in elevating the pharynx during swallowing. Correct answer: 3rd arch.
Question 5
The cricothyroid muscle originates from which pharyngeal arch?
a) 2nd
b) 3rd
c) 4th
d) 6th
Explanation: The cricothyroid muscle arises from the 4th pharyngeal arch and is innervated by the external branch of superior laryngeal nerve (branch of vagus). This distinguishes it from other intrinsic laryngeal muscles, which are from 6th arch. Correct answer: 4th arch.
Question 6
Which pharyngeal pouch gives rise to the palatine tonsil?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: The palatine tonsil develops from the endoderm of the 2nd pharyngeal pouch. It plays a role in immune defense and is part of Waldeyer’s ring. Correct answer: 2nd pouch.
Question 7
DiGeorge syndrome results from abnormal development of which pharyngeal pouches?
a) 1st & 2nd
b) 2nd & 3rd
c) 3rd & 4th
d) 4th only
Explanation: DiGeorge syndrome arises due to failure of 3rd and 4th pharyngeal pouches, leading to thymic hypoplasia, hypocalcemia, and cardiac defects. Correct answer: 3rd & 4th.
Question 8
Which cranial nerve innervates most intrinsic laryngeal muscles from the 6th arch?
a) Glossopharyngeal
b) Vagus - recurrent laryngeal
c) Hypoglossal
d) Accessory
Explanation: Intrinsic laryngeal muscles, except cricothyroid, are derived from 6th pharyngeal arch and supplied by recurrent laryngeal nerve (branch of vagus). Correct answer: Vagus - recurrent laryngeal.
Question 9
Treacher Collins syndrome results from maldevelopment of which arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: Treacher Collins syndrome (mandibulofacial dysostosis) results from abnormal neural crest cell migration affecting the 1st arch. It causes craniofacial abnormalities, micrognathia, and cleft palate. Correct answer: 1st arch.
Question 10
Cleft palate is most directly related to abnormal fusion of which structures?
a) Pharyngeal arches
b) Maxillary processes
c) Mandibular processes
d) Hyoid arches
Explanation: Cleft palate results from failure of fusion of the maxillary processes and palatal shelves during embryogenesis, not directly from arch failure. Correct answer: Maxillary processes.
Question 11
Which nerve is associated with the 3rd pharyngeal arch?
a) Trigeminal
b) Facial
c) Glossopharyngeal
d) Vagus
Explanation: The 3rd pharyngeal arch is associated with glossopharyngeal nerve (cranial nerve IX), which supplies stylopharyngeus muscle and contributes to oropharyngeal sensation. Correct answer: Glossopharyngeal.
Chapter: Embryology
Topic: Germ Cell Development
Subtopic: Origin and Migration of Primordial Germ Cells
Keywords:
Primordial germ cells: Precursors of gametes (sperm and ova) that originate outside the gonads.
Yolk sac: Extraembryonic structure providing nutrition and site of origin of primordial germ cells.
Genital ridge: Area where primordial germ cells migrate and form future gonads.
Neural crest: Source of melanocytes, craniofacial structures, and peripheral neurons, not germ cells.
Somatopleuritic mesoderm: Contributes to body wall and limbs, not germ cell origin.
Clinical relevance: Errors in germ cell migration can lead to gonadal dysgenesis or germ cell tumors.
Lead Question - 2012
Primordial germ cells are derived from:
a) Neural crest
b) Genital ridge
c) Somatopleuritic mesoderm
d) Yolk sac
Explanation: Primordial germ cells originate in the endoderm of the yolk sac, migrate through the dorsal mesentery, and settle in the genital ridge to form gonads. This migration is crucial for gametogenesis. Correct answer is Yolk sac.
Guessed Question 1
At what week do primordial germ cells migrate to the genital ridge?
a) 2nd week
b) 4th week
c) 6th week
d) 8th week
Explanation: Primordial germ cells migrate from the yolk sac to the genital ridge by the 6th week of embryonic development. Their arrival triggers differentiation into oogonia or spermatogonia. Correct answer is 6th week.
Guessed Question 2
Failure of primordial germ cell migration can result in?
a) Turner's syndrome
b) Germ cell tumors
c) Neural tube defects
d) Holoprosencephaly
Explanation: If primordial germ cells fail to migrate properly, ectopic germ cells may persist and transform into germ cell tumors like teratomas, often seen in sacrococcygeal regions. Correct answer is Germ cell tumors.
Guessed Question 3
The genital ridge differentiates into?
a) Kidneys
b) Gonads
c) Adrenal cortex
d) Pancreas
Explanation: The genital ridge, after receiving migrating primordial germ cells, develops into testes in males or ovaries in females depending on genetic and hormonal influences. Correct answer is Gonads.
Guessed Question 4
Which structure guides the migration of primordial germ cells?
a) Amnion
b) Dorsal mesentery
c) Neural crest
d) Umbilical cord
Explanation: Primordial germ cells migrate via the dorsal mesentery of the hindgut to reach the genital ridge. This pathway is essential for normal gonadal development. Correct answer is Dorsal mesentery.
Guessed Question 5
Which tumor commonly arises from misplaced primordial germ cells?
a) Osteosarcoma
b) Teratoma
c) Medulloblastoma
d) Neuroblastoma
Explanation: Teratomas arise from pluripotent primordial germ cells that fail to reach their destination. They can contain tissues from all germ layers. Correct answer is Teratoma.
Guessed Question 6
Primordial germ cells first appear in which layer?
a) Mesoderm
b) Endoderm
c) Ectoderm
d) Neural crest
Explanation: Primordial germ cells originate from the endoderm of the yolk sac wall before migrating to the genital ridge. Correct answer is Endoderm.
Guessed Question 7
Abnormal location of primordial germ cells can lead to?
a) Gonadal dysgenesis
b) Renal agenesis
c) Adrenal hyperplasia
d) Anencephaly
Explanation: Misplaced germ cells that fail to colonize the genital ridge may result in gonadal dysgenesis or infertility. Correct answer is Gonadal dysgenesis.
Guessed Question 8
Which signaling pathway is critical for primordial germ cell specification?
a) Sonic Hedgehog
b) BMP (Bone Morphogenetic Protein)
c) Notch
d) Wnt
Explanation: Bone Morphogenetic Protein (BMP) signaling from extraembryonic tissues plays a central role in specifying primordial germ cells. Correct answer is BMP.
Guessed Question 9
In which clinical condition are primordial germ cells absent in the gonads?
a) Klinefelter syndrome
b) Turner syndrome
c) Androgen insensitivity
d) Down syndrome
Explanation: In Turner syndrome (45,X), streak ovaries form due to failure of primordial germ cell colonization. Correct answer is Turner syndrome.
Guessed Question 10
Primordial germ cells give rise to?
a) Spermatogonia and Oogonia
b) Sertoli and Granulosa cells
c) Leydig and Theca cells
d) Adrenal cortical cells
Explanation: Primordial germ cells differentiate into spermatogonia in males and oogonia in females, initiating gametogenesis. Correct answer is Spermatogonia and Oogonia.
Subtopic: Blastocyst Formation and Differentiation
Keywords & Definitions:
Blastocyst: A structure formed in early embryogenesis, consisting of an outer layer and an inner cell mass.
Trophoblast: Outer layer of blastocyst that contributes to placenta formation.
Primitive streak: A structure that forms on the blastodisc and initiates gastrulation.
Yolk sac: An extraembryonic membrane involved in nutrient transfer in early development.
Embryo proper: The developing organism itself, arising from the inner cell mass.
Gastrulation: Process in which the three germ layers form from the epiblast.
Inner cell mass (ICM): Cluster of cells inside the blastocyst that gives rise to the embryo proper.
Placenta: Organ that develops from trophoblast and maternal tissue, facilitating nutrient exchange.
Extraembryonic membranes: Structures like yolk sac, amnion, and chorion that support the embryo.
Implantation: Process by which the blastocyst attaches to the uterine wall.
Lead Question - 2012:
The outer layer of the blastocyst forms ?
a) Primitive streak
b) Yolk sac
c) Embryo proper
d) Trophoblast
Explanation & Answer:
The correct answer is d) Trophoblast. The outer layer of the blastocyst is called the trophoblast, which plays a critical role in implantation and forms the fetal part of the placenta. The inner cell mass develops into the embryo proper, while the yolk sac and primitive streak arise later during development.
Q2. Which structure arises from the inner cell mass of the blastocyst?
a) Trophoblast
b) Primitive streak
c) Embryo proper
d) Chorion
Explanation & Answer:
The inner cell mass (ICM) of the blastocyst gives rise to the embryo proper (option c), which will develop into the fetus and some extraembryonic tissues. The trophoblast forms the outer layer, contributing to placenta formation.
Q3. The primitive streak appears during which embryonic stage?
a) Morula
b) Blastocyst
c) Gastrulation
d) Neurulation
Explanation & Answer:
The primitive streak forms during gastrulation (option c), marking the beginning of germ layer formation. It is not present at the morula or blastocyst stage and precedes neurulation.
Q4 (Clinical). Failure of proper trophoblast invasion can lead to which condition?
a) Ectopic pregnancy
b) Pre-eclampsia
c) Hydatidiform mole
d) Placenta previa
Explanation & Answer:
Insufficient trophoblast invasion into the uterine wall can cause pre-eclampsia (option b), a pregnancy complication characterized by hypertension and organ dysfunction.
Q5. The yolk sac in humans is primarily responsible for?
a) Formation of placenta
b) Early hematopoiesis
c) Neural tube development
d) Formation of amniotic fluid
Explanation & Answer:
The yolk sac (option b) acts as a site for early blood cell formation (hematopoiesis) and nutrient transfer during early embryonic life before the placenta fully develops.
Q6. During implantation, the trophoblast differentiates into?
a) Cytotrophoblast and syncytiotrophoblast
b) Epiblast and hypoblast
c) Amnion and yolk sac
d) Mesoderm and endoderm
Explanation & Answer:
The trophoblast differentiates into cytotrophoblast and syncytiotrophoblast (option a), which facilitate embryo implantation and invasion into the uterine lining.
Q7. Which layer eventually forms the amnion?
a) Inner cell mass
b) Trophoblast
c) Primitive streak
d) Hypoblast
Explanation & Answer:
The amnion develops from the epiblast, which is part of the inner cell mass (option a), forming a fluid-filled cavity that protects the embryo.
Q8. Which hormone is secreted by the trophoblast soon after implantation?
a) Estrogen
b) Progesterone
c) Human chorionic gonadotropin (hCG)
d) Luteinizing hormone (LH)
Explanation & Answer:
The syncytiotrophoblast secretes human chorionic gonadotropin (hCG) (option c), which maintains the corpus luteum and supports early pregnancy.
Q9. Primitive streak formation marks the beginning of which process?
a) Fertilization
b) Cleavage
c) Gastrulation
d) Organogenesis
Explanation & Answer:
The appearance of the primitive streak (option c) initiates gastrulation, during which the three germ layers—ectoderm, mesoderm, and endoderm—are formed.
Q10 (Clinical). Hydatidiform mole arises due to abnormal proliferation of which embryonic layer?
a) Inner cell mass
b) Trophoblast
c) Primitive streak
d) Hypoblast
Explanation & Answer:
Hydatidiform mole results from abnormal trophoblastic proliferation (option b), leading to a mass of swollen chorionic villi and pregnancy loss
Subtopic: Parathyroid Gland Development
Keywords & Definitions:
Pharyngeal arches: Embryonic structures that give rise to head and neck components.
Inferior parathyroid gland: Endocrine glands regulating calcium homeostasis, derived embryonically from the 3rd pharyngeal pouch.
Superior parathyroid gland: Derived from the 4th pharyngeal pouch.
Pharyngeal pouches: Internal endodermal outpouchings between pharyngeal arches.
Thymus: Develops from the 3rd pharyngeal pouch along with inferior parathyroids.
Branchial apparatus: Includes arches, pouches, clefts, and membranes involved in neck and facial development.
Calcium regulation: Parathyroid glands secrete parathyroid hormone (PTH) to maintain blood calcium levels.
Embryonic migration: Inferior parathyroids migrate downward with the thymus during development.
Developmental anomalies: Can lead to conditions like DiGeorge syndrome (3rd and 4th pouch defects).
Endoderm: The inner germ layer lining pharyngeal pouches, source of parathyroids and thymus.
Lead Question - 2012:
Inferior parathyroid develops from which arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation & Answer:
The correct answer is c) 3rd arch (more precisely, the 3rd pharyngeal pouch). The inferior parathyroid glands arise embryologically from the endoderm of the 3rd pouch, along with the thymus. During development, they migrate caudally to their final position, which is lower than the superior parathyroids derived from the 4th pouch.
Q2. The superior parathyroid gland develops from which pharyngeal pouch?
a) 2nd
b) 3rd
c) 4th
d) 1st
Explanation & Answer:
The superior parathyroid gland develops from the 4th pharyngeal pouch (option c). It remains superior in position as compared to the inferior parathyroids which migrate downward.
Q3. Which structure develops from the 3rd pharyngeal pouch along with the inferior parathyroids?
a) Thymus
b) Thyroid
c) Parafollicular cells
d) Auditory tube
Explanation & Answer:
The thymus develops from the 3rd pharyngeal pouch along with the inferior parathyroid glands (option a). Both structures migrate caudally during embryogenesis.
Q4 (Clinical). DiGeorge syndrome is caused by developmental failure of which pharyngeal pouches?
a) 1st and 2nd
b) 3rd and 4th
c) 2nd and 3rd
d) 4th and 5th
Explanation & Answer:
DiGeorge syndrome results from failure of development of the 3rd and 4th pharyngeal pouches (option b), causing defects in the thymus and parathyroid glands leading to immunodeficiency and hypocalcemia.
Q5. Which germ layer forms the parathyroid glands?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Neural crest cells
Explanation & Answer:
The parathyroid glands develop from the endoderm (option c) lining the pharyngeal pouches. Neural crest cells contribute to other structures but not the parathyroids themselves.
Q6. During migration, the inferior parathyroid glands move alongside which organ?
a) Thyroid gland
b) Thymus
c) Parotid gland
d) Larynx
Explanation & Answer:
Inferior parathyroids migrate with the thymus (option b) from the 3rd pharyngeal pouch to their final lower position near the lower pole of the thyroid gland.
Q7. Which artery supplies the inferior parathyroid gland?
a) Superior thyroid artery
b) Inferior thyroid artery
c) Lingual artery
d) Facial artery
Explanation & Answer:
The inferior thyroid artery (option b) supplies the inferior parathyroid glands, which is important clinically during thyroid surgeries to avoid hypoparathyroidism.
Q8. Hypocalcemia in a newborn may result from failure of development of which structure?
a) Superior parathyroid
b) Inferior parathyroid
c) Both parathyroids
d) Adrenal medulla
Explanation & Answer:
Failure of development of either the inferior or superior parathyroids (option c) can lead to hypocalcemia due to decreased parathyroid hormone production.
Q9. The 1st pharyngeal pouch gives rise to?
a) Middle ear cavity and auditory tube
b) Thymus
c) Inferior parathyroid
d) Superior parathyroid
Explanation & Answer:
The 1st pharyngeal pouch (option a) forms the middle ear cavity and auditory (Eustachian) tube, not the parathyroid glands.
Q10 (Clinical). A patient with absent thymus and hypoparathyroidism may have a deletion of which chromosome region?
a) 22q11.2
b) 15q11
c) 7q31
d) 11p15
Explanation & Answer:
Deletion of chromosome 22q11.2 (option a) causes DiGeorge syndrome, characterized by absent thymus, hypoparathyroidism, and cardiac defects.
Subtopic: Origin of Glial Cells
Keywords & Definitions:
Mesoderm: The middle germ layer giving rise to muscles, blood vessels, connective tissue, and microglia.
Ectoderm: The outer germ layer from which neurons and most glial cells (astrocytes, oligodendrocytes, ependymal cells) develop.
Microglial cells: CNS immune cells derived from mesodermal origin (yolk sac macrophages).
Astrocytes: Star-shaped glial cells providing structural and metabolic support, derived from neuroectoderm.
Oligodendrocytes: Myelin-forming cells in CNS, originating from neuroectoderm.
Ependymal cells: Line ventricles and central canal of spinal cord; derived from neuroectoderm.
Neuroglia: Supporting cells of nervous system including astrocytes, oligodendrocytes, microglia, and ependymal cells.
Yolk sac macrophages: Early embryonic mesodermal cells that migrate to CNS as microglia.
CNS immune surveillance: Microglia function as resident macrophages in brain and spinal cord.
Neuroectoderm: Specialized ectoderm that forms the nervous system structures.
Lead Question - 2012:
Mesodermal in origin?
a) Astrocytes
b) Oligodendrocytes
c) Ependymal cells
d) Microglial cells
Explanation & Answer:
The correct answer is d) Microglial cells. Microglia are the only glial cells derived from the mesoderm, specifically from yolk sac macrophages. All other glial cells such as astrocytes, oligodendrocytes, and ependymal cells originate from the neuroectoderm (ectodermal layer). Microglia act as the resident immune cells in the central nervous system, providing defense and cleanup.
Q2. Which glial cell is responsible for myelin formation in the CNS?
a) Microglia
b) Oligodendrocytes
c) Astrocytes
d) Ependymal cells
Explanation & Answer:
Oligodendrocytes (option b) produce myelin sheaths around axons in the CNS, increasing conduction velocity. Unlike Schwann cells in the peripheral nervous system, oligodendrocytes can myelinate multiple axons simultaneously.
Q3. Which cells line the ventricles of the brain?
a) Astrocytes
b) Oligodendrocytes
c) Ependymal cells
d) Microglia
Explanation & Answer:
Ependymal cells (option c) line the ventricular system and central canal of the spinal cord. They facilitate cerebrospinal fluid circulation and act as a barrier between CSF and nervous tissue.
Q4. Which glial cell provides structural and metabolic support to neurons?
a) Astrocytes
b) Microglia
c) Oligodendrocytes
d) Ependymal cells
Explanation & Answer:
Astrocytes (option a) support neurons structurally and metabolically by maintaining the blood-brain barrier, regulating ion balance, and supplying nutrients.
Q5 (Clinical). Microglial activation is primarily seen in which condition?
a) Multiple sclerosis
b) Alzheimer's disease
c) Meningitis
d) Parkinson’s disease
Explanation & Answer:
Microglial activation (option b) is a hallmark of Alzheimer’s disease, where these immune cells contribute to neuroinflammation and clearance of amyloid plaques.
Q6. Which cell type forms the blood-brain barrier?
a) Microglia
b) Astrocytes
c) Ependymal cells
d) Oligodendrocytes
Explanation & Answer:
Astrocyte end-feet (option b) contribute to the blood-brain barrier by surrounding endothelial cells and regulating molecule passage from blood to brain.
Q7. The primary immune defense cells in the CNS are:
a) Oligodendrocytes
b) Microglia
c) Astrocytes
d) Ependymal cells
Explanation & Answer:
Microglia (option b) serve as the resident macrophages of the CNS, performing immune surveillance, phagocytosis, and release of cytokines.
Q8. Which glial cells originate from the neuroectoderm?
a) Microglia only
b) Astrocytes, oligodendrocytes, ependymal cells
c) Microglia and astrocytes
d) All glial cells
Explanation & Answer:
Astrocytes, oligodendrocytes, and ependymal cells (option b) develop from the neuroectoderm, whereas microglia are mesoderm-derived.
Q9 (Clinical). Which glial cell dysfunction is implicated in demyelinating diseases?
a) Astrocytes
b) Oligodendrocytes
c) Microglia
d) Ependymal cells
Explanation & Answer:
Oligodendrocyte damage (option b) leads to demyelination in diseases like multiple sclerosis, impairing nerve conduction.
Q10. Which cells contribute to cerebrospinal fluid (CSF) production?
a) Microglia
b) Ependymal cells
c) Astrocytes
d) Oligodendrocytes
Explanation & Answer:
Ependymal cells (option b), especially specialized choroid plexus epithelium, secrete cerebrospinal fluid and line the ventricles.
Subtopic: Formation and Closure of Fossa Ovalis
Keywords & Definitions:
Fossa ovalis: A depression in the right atrium, remnant of the fetal foramen ovale.
Foramen ovale: A fetal opening in the interatrial septum allowing blood to bypass lungs.
Septum primum: The first interatrial septum, grows downward towards endocardial cushions.
Septum secundum: The second crescent-shaped septum overlapping foramen ovale.
Endocardial cushion: Tissue in the atrioventricular canal that contributes to septa and valves.
Interatrial septum: The wall separating left and right atria in the heart.
Fusion: Joining of embryonic structures to form a definitive anatomical part.
Patent foramen ovale: Failure of the foramen ovale to close after birth.
Left atrial pressure: Pressure that pushes septa to fuse after birth.
Embryonic heart development: The process by which cardiac chambers and septa form.
Lead Question - 2012:
Fossa ovalis closes because of the fusion of?
a) Septum primum + Endocardial cushion
b) Septum secundum + Endocardial cushion
c) Septum primum + Septum secundum
d) None
Explanation & Answer:
The correct answer is c) Septum primum + Septum secundum. After birth, increased left atrial pressure pushes the septum primum against the septum secundum, leading to their fusion which closes the foramen ovale functionally and forms the fossa ovalis. The endocardial cushions contribute to atrioventricular septation but not directly to this fusion. Failure to close leads to a patent foramen ovale.
Q2. The foramen ovale allows blood flow between which two chambers in fetal life?
a) Right atrium to left atrium
b) Left atrium to right atrium
c) Right ventricle to left ventricle
d) Left ventricle to right ventricle
Explanation & Answer:
The foramen ovale (option a) permits oxygenated blood to flow from the right atrium directly to the left atrium, bypassing the nonfunctional fetal lungs.
Q3. Which embryonic structure forms the muscular part of the interventricular septum?
a) Endocardial cushions
b) Bulbus cordis
c) Primitive ventricle
d) Truncus arteriosus
Explanation & Answer:
The muscular interventricular septum (option c) develops from the primitive ventricle, separating left and right ventricles during heart development.
Q4. Patent foramen ovale can lead to which clinical condition?
a) Cyanotic congenital heart disease
b) Paradoxical embolism
c) Aortic stenosis
d) Mitral valve prolapse
Explanation & Answer:
Patent foramen ovale (option b) can allow venous thrombi to bypass the lungs and enter systemic circulation, causing paradoxical embolism, stroke, or transient ischemic attacks.
Q5 (Clinical). A newborn with persistent right-to-left shunt through foramen ovale may present with?
a) Cyanosis
b) Tachycardia
c) Hypertension
d) Bradycardia
Explanation & Answer:
Persistent right-to-left shunting (option a) causes deoxygenated blood to bypass lungs, resulting in cyanosis and hypoxemia after birth.
Q6. The endocardial cushions contribute to the formation of?
a) Interventricular septum only
b) Atrioventricular septum and valves
c) Aortic arch
d) Pulmonary veins
Explanation & Answer:
Endocardial cushions (option b) are vital for forming atrioventricular septum and valves, separating atria and ventricles and forming mitral and tricuspid valves.
Q7. Which septum forms the initial partition in the primitive atrium?
a) Septum secundum
b) Septum primum
c) Endocardial cushion
d) Ventricular septum
Explanation & Answer:
The septum primum (option b) is the first structure to grow downward from the atrial roof, starting the separation of the primitive atrium into right and left atria.
Q8. The septum secundum forms a partial wall on which side of the heart?
a) Left atrium
b) Right atrium
c) Left ventricle
d) Right ventricle
Explanation & Answer:
The septum secundum (option b) grows on the right atrial side, overlapping the foramen ovale, allowing a flap valve mechanism to regulate fetal blood flow.
Q9 (Clinical). Atrial septal defect is most commonly due to failure of?
a) Fusion of septum primum and secundum
b) Closure of ductus arteriosus
c) Formation of endocardial cushions
d) Septation of ventricles
Explanation & Answer:
Atrial septal defect (option a) often results from incomplete fusion of septum primum and septum secundum, causing persistent interatrial communication and left-to-right shunt.
Q10. After birth, the functional closure of the foramen ovale is primarily due to?
a) Increase in right atrial pressure
b) Increase in left atrial pressure
c) Decrease in systemic vascular resistance
d) Constriction of ductus arteriosus
Explanation & Answer:
The increased left atrial pressure after birth (option b) pushes the septum primum against septum secundum, functionally closing the foramen ovale and preventing blood flow between atria.
Subtopic: Ectodermal Derivatives
Keywords & Definitions:
Ectoderm: Outer germ layer forming skin, nervous system, and certain sensory organs.
Endoderm: Innermost germ layer forming the lining of the gut, respiratory tract, and glands.
Mesoderm: Middle germ layer forming muscles, bones, circulatory system, and connective tissues.
Lens: Transparent structure of the eye focusing light on the retina.
Eustachian tube: Tube connecting the middle ear to the nasopharynx, equalizing pressure.
Brain: Central organ of the nervous system derived from neural tube.
Retina: Light-sensitive tissue at the back of the eye derived from neural ectoderm.
Neural crest cells: Ectodermal cells contributing to peripheral nerves, melanocytes, and craniofacial structures.
Pharyngeal pouches: Endodermal outpocketings contributing to ear, tonsils, and glands.
Embryonic germ layers: Three primary cell layers in early development—ectoderm, mesoderm, endoderm.
Q1 (2012). All are derived from ectoderm except?
a) Lens
b) Eustachian tube
c) Brain
d) Retina
Explanation & Answer:
Correct answer: b) Eustachian tube.
The Eustachian tube develops from the first pharyngeal pouch, which is endodermal in origin. Lens, brain, and retina are ectodermal derivatives. Lens develops from surface ectoderm, brain and retina from neural ectoderm. Knowing germ layer origins helps in identifying congenital anomalies.
Q2. Which ectodermal structure forms the enamel of teeth?
a) Neural crest
b) Surface ectoderm
c) Endoderm
d) Mesoderm
Explanation & Answer:
Correct answer: b) Surface ectoderm.
Enamel is produced by ameloblasts derived from surface ectoderm. The underlying dentin and pulp originate from mesodermal tissues. This distinction is important in dental pathology and congenital tooth disorders.
Q3. The pituitary gland's anterior lobe develops from:
a) Neuroectoderm
b) Surface ectoderm
c) Endoderm
d) Mesoderm
Explanation & Answer:
Correct answer: b) Surface ectoderm.
The anterior pituitary (adenohypophysis) develops from Rathke’s pouch, an outgrowth of surface ectoderm from the stomodeum. The posterior pituitary (neurohypophysis) arises from neuroectoderm.
Q4 (Clinical). A newborn presents with congenital absence of the pineal gland. Which germ layer was likely affected?
a) Surface ectoderm
b) Neuroectoderm
c) Endoderm
d) Mesoderm
Explanation & Answer:
Correct answer: b) Neuroectoderm.
The pineal gland originates from neuroectoderm of the diencephalon. Damage to this layer during embryogenesis can impair melatonin production and disrupt circadian rhythm.
Q5. Which is NOT a derivative of neural crest cells?
a) Melanocytes
b) Adrenal medulla
c) Schwann cells
d) Retina
Explanation & Answer:
Correct answer: d) Retina.
Retina arises from neural ectoderm, not neural crest. Neural crest cells contribute to melanocytes, adrenal medulla, craniofacial cartilage, and Schwann cells.
Q6. Cornea is derived from:
a) Ectoderm and mesoderm
b) Endoderm
c) Mesoderm only
d) Ectoderm only
Explanation & Answer:
Correct answer: a) Ectoderm and mesoderm.
The corneal epithelium is derived from surface ectoderm, while stroma and endothelium arise from mesodermal mesenchyme.
Q7 (Clinical). A defect in neural tube closure will primarily affect which ectodermal derivatives?
a) Peripheral nerves
b) Brain and spinal cord
c) Adrenal cortex
d) Epidermis
Explanation & Answer:
Correct answer: b) Brain and spinal cord.
Neural tube defects, such as spina bifida or anencephaly, arise from failure of neural ectoderm closure, affecting the central nervous system.
Q8. Which pharyngeal pouch gives rise to the Eustachian tube?
a) First
b) Second
c) Third
d) Fourth
Explanation & Answer:
Correct answer: a) First.
The first pharyngeal pouch develops into the Eustachian tube and middle ear cavity, lined by endoderm.
Q9. Epidermis of skin is derived from:
a) Mesoderm
b) Endoderm
c) Surface ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: c) Surface ectoderm.
Surface ectoderm forms the epidermis, hair, nails, and glands of the skin. The dermis is mostly mesodermal in origin.
Q10. The inner ear’s membranous labyrinth develops from:
a) Endoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Surface ectoderm.
The otic placode, a thickening of surface ectoderm, invaginates to form the membranous labyrinth of the inner ear.
Q11. Which part of the eye is mesodermal in origin?
a) Lens
b) Retina
c) Choroid
d) Corneal epithelium
Explanation & Answer:
Correct answer: c) Choroid.
The choroid, sclera, and part of the cornea are mesodermal derivatives, providing vascular supply and structural support to the eye.
Subtopic: Endodermal Derivatives
Keywords & Definitions:
Endoderm: Innermost germ layer forming epithelial lining of the gastrointestinal tract, respiratory tract, and associated glands.
Gall bladder: A small sac beneath the liver storing and releasing bile, derived from endoderm.
Lens: Transparent biconvex structure of the eye, derived from surface ectoderm.
Spleen: Lymphoid organ derived from mesoderm, involved in immune response and RBC breakdown.
Lymph nodes: Secondary lymphoid organs derived from mesoderm, filtering lymph fluid.
Pharyngeal pouches: Endodermal outpocketings forming glands and ear structures.
Pancreas: Digestive and endocrine gland derived from endoderm.
Thyroid gland: Endocrine gland in the neck, derived from endoderm of the floor of the pharynx.
Respiratory tract: Airway system from nasal cavity to alveoli, derived from foregut endoderm.
Urinary bladder epithelium: Inner lining of the bladder derived from endoderm of the urogenital sinus.
Q1 (2012). Which of the following is derived from endoderm?
a) Gall bladder
b) Lens
c) Spleen
d) Lymph nodes
Explanation & Answer:
Correct answer: a) Gall bladder.
The gall bladder develops from the hepatic diverticulum of the foregut endoderm. Lens is from surface ectoderm, spleen and lymph nodes are mesodermal. Recognizing embryonic origins is crucial for understanding congenital malformations, such as biliary atresia, which arises from faulty endodermal development.
Q2. The epithelial lining of the trachea is derived from:
a) Mesoderm
b) Endoderm
c) Ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm.
The respiratory epithelium originates from the foregut endoderm, while surrounding cartilage and smooth muscle come from splanchnic mesoderm. This distinction explains why certain congenital airway defects have combined epithelial and structural abnormalities.
Q3. The thyroid gland originates from:
a) Endoderm of primitive pharynx
b) Mesoderm
c) Neural crest
d) Ectoderm
Explanation & Answer:
Correct answer: a) Endoderm of primitive pharynx.
The thyroid develops from a median endodermal thickening in the floor of the pharynx. Migration defects can cause ectopic thyroid tissue along the thyroglossal duct pathway.
Q4 (Clinical). A newborn with respiratory distress is found to have tracheoesophageal fistula. Which germ layer defect is implicated?
a) Ectoderm
b) Endoderm
c) Mesoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm.
Both trachea and esophagus arise from the foregut endoderm. Separation failure during development results in a fistula, causing aspiration and feeding difficulties in neonates.
Q5. Which is NOT an endodermal derivative?
a) Liver
b) Pancreas
c) Adrenal medulla
d) Gall bladder
Explanation & Answer:
Correct answer: c) Adrenal medulla.
Adrenal medulla originates from neural crest cells (ectodermal origin), while liver, pancreas, and gall bladder are from foregut endoderm.
Q6. Epithelial lining of the urinary bladder develops from:
a) Mesoderm
b) Endoderm of urogenital sinus
c) Ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm of urogenital sinus.
The inner epithelium of the bladder is from endoderm, while connective tissue and muscle layers are from splanchnic mesoderm.
Q7 (Clinical). A patient with chronic pancreatitis undergoes histological examination. The acinar cells are derived from which germ layer?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: a) Endoderm.
Both exocrine and endocrine parts of the pancreas originate from endodermal buds of the foregut, explaining the shared embryological basis for pancreatic and biliary anomalies.
Q8. Which part of the ear is endodermal in origin?
a) Tympanic membrane
b) Eustachian tube
c) Pinna
d) External auditory canal
Explanation & Answer:
Correct answer: b) Eustachian tube.
The Eustachian tube and middle ear cavity arise from the first pharyngeal pouch (endoderm), while pinna and external canal are ectodermal.
Q9. The epithelial lining of the anal canal above the pectinate line is derived from:
a) Ectoderm
b) Endoderm
c) Mesoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm.
Above the pectinate line, the anal canal develops from hindgut endoderm, while below it comes from ectoderm, explaining different lymphatic drainage and nerve supply.
Q10. Which pharyngeal pouch gives rise to the thymus?
a) First
b) Second
c) Third
d) Fourth
Explanation & Answer:
Correct answer: c) Third.
The thymus develops from the ventral part of the third pharyngeal pouch (endoderm), migrating to the anterior mediastinum.
Q11. Which of the following is an endodermal derivative?
a) Parathyroid gland
b) Epidermis
c) Skeletal muscle
d) Cornea
Explanation & Answer:
Correct answer: a) Parathyroid gland.
Parathyroid glands develop from the dorsal portions of the third and fourth pharyngeal pouches (endodermal origin), playing a key role in calcium regulation.
Subtopic: Development of the Peritoneal Cavity
Keywords & Definitions:
Mesenchyme: Embryonic connective tissue derived mainly from mesoderm, forming connective tissues, blood, and lymphatic structures.
Intraembryonic coelom: The cavity formed within the lateral plate mesoderm during embryonic folding, giving rise to body cavities.
Ectoderm: The outer germ layer forming the nervous system, epidermis, and related structures.
Endoderm: The innermost germ layer forming epithelial linings of the gastrointestinal tract, respiratory tract, and glands.
Peritoneal cavity: The space within the abdomen lined by peritoneum, housing abdominal organs.
Pleural cavity: Thoracic cavity surrounding each lung.
Pericardial cavity: Space enclosing the heart within the pericardium.
Lateral plate mesoderm: Mesoderm layer split into somatic and splanchnic layers, forming body cavities and their linings.
Septum transversum: Mesodermal tissue contributing to diaphragm formation.
Mesentery: Double layer of peritoneum that suspends and supports organs in the abdominal cavity.
Q1 (2012). Development of peritoneal cavity is from?
a) Mesenchyme
b) Intraembryonic coelom
c) Ectoderm
d) Endoderm
Explanation & Answer:
Correct answer: b) Intraembryonic coelom.
The peritoneal cavity originates from the intraembryonic coelom formed within the lateral plate mesoderm during the 3rd week. This cavity later partitions into the peritoneal, pleural, and pericardial cavities. Proper development is crucial, as abnormal folding or partitioning can lead to congenital diaphragmatic hernias.
Q2. The intraembryonic coelom first appears during:
a) 1st week
b) 2nd week
c) 3rd week
d) 4th week
Explanation & Answer:
Correct answer: c) 3rd week.
The intraembryonic coelom develops as spaces appear within the lateral plate mesoderm during the 3rd week of development, eventually fusing to form a horseshoe-shaped cavity that becomes the basis of the major body cavities.
Q3. Which embryonic layer forms the lining epithelium of the peritoneal cavity?
a) Somatic mesoderm
b) Splanchnic mesoderm
c) Ectoderm
d) Endoderm
Explanation & Answer:
Correct answer: a) Somatic mesoderm.
The parietal peritoneum is derived from somatic mesoderm, while visceral peritoneum is derived from splanchnic mesoderm. This explains why parietal peritoneum pain is sharp and well localized, while visceral pain is dull and poorly localized.
Q4 (Clinical). A neonate is diagnosed with omphalocele. The developmental defect primarily involves:
a) Ectodermal folding defect
b) Endodermal failure
c) Intraembryonic coelom partition defect
d) Failure of gut retraction
Explanation & Answer:
Correct answer: d) Failure of gut retraction.
In omphalocele, midgut fails to return to the peritoneal cavity after physiological herniation. The peritoneal cavity’s development and folding are essential to prevent this defect.
Q5. The septum transversum plays a major role in the formation of:
a) Peritoneal cavity
b) Diaphragm
c) Pleura
d) Pericardium
Explanation & Answer:
Correct answer: b) Diaphragm.
The septum transversum forms the central tendon of the diaphragm and partially separates the thoracic and abdominal cavities before complete partitioning by the pleuroperitoneal membranes.
Q6. Which structure separates the peritoneal cavity from the pleural cavities in early development?
a) Septum transversum
b) Pleuroperitoneal membranes
c) Diaphragmatic muscle
d) Mesentery
Explanation & Answer:
Correct answer: b) Pleuroperitoneal membranes.
These membranes grow to close the pericardioperitoneal canals, completing the separation of the pleural and peritoneal cavities.
Q7 (Clinical). A defect in closure of the pleuroperitoneal membrane results in:
a) Hiatal hernia
b) Bochdalek hernia
c) Morgagni hernia
d) Omphalocele
Explanation & Answer:
Correct answer: b) Bochdalek hernia.
Bochdalek hernia is a posterolateral congenital diaphragmatic hernia caused by failure of pleuroperitoneal membrane fusion, allowing abdominal organs into the thoracic cavity.
Q8. The mesentery suspending the midgut from the dorsal body wall is derived from:
a) Somatic mesoderm
b) Splanchnic mesoderm
c) Ectoderm
d) Endoderm
Explanation & Answer:
Correct answer: b) Splanchnic mesoderm.
The dorsal mesentery is from splanchnic mesoderm and provides a pathway for blood vessels, lymphatics, and nerves to the gut.
Q9. Which event marks the final separation of the peritoneal and pericardial cavities?
a) Folding of the embryo
b) Formation of the diaphragm
c) Closure of the neural tube
d) Formation of the gut tube
Explanation & Answer:
Correct answer: b) Formation of the diaphragm.
Completion of the diaphragm closes the communication between the thoracic and abdominal cavities.
Q10. The visceral peritoneum is derived from:
a) Somatic mesoderm
b) Splanchnic mesoderm
c) Endoderm
d) Ectoderm
Explanation & Answer:
Correct answer: b) Splanchnic mesoderm.
The splanchnic mesoderm forms the visceral layer of the peritoneum covering abdominal organs, in contrast to the somatic mesoderm-derived parietal layer.
Q11. The peritoneal cavity communicates with the extraembryonic coelom through:
a) Primitive streak
b) Umbilical ring
c) Neurenteric canal
d) Pharyngeal membrane
Explanation & Answer:
Correct answer: b) Umbilical ring.
Early in development, the intraembryonic coelom is continuous with the extraembryonic coelom at the umbilical ring, allowing passage of yolk sac and connecting stalk structures.
Subtopic: Cytotrophoblast Invasion
Keywords & Definitions:
Cytotrophoblast: Inner layer of trophoblast cells that proliferate and invade maternal tissues during implantation.
Decidua parietalis: The part of the decidua lining the non-placental regions of the uterus.
Decidua basalis: The part of the decidua beneath the implanted embryo, forming maternal part of the placenta.
Decidua capsularis: The decidual layer covering the implanted embryo and enclosing the conceptus.
Trophoblast: The outer cell layer of the blastocyst that participates in implantation and placenta formation.
Implantation: Process where the blastocyst embeds into the uterine lining.
Syncytiotrophoblast: Multinucleated outer layer of trophoblast responsible for invading the endometrium and producing hCG.
Uterine stroma: Connective tissue of the uterus that becomes decidua during pregnancy.
hCG (Human chorionic gonadotropin): Hormone secreted by syncytiotrophoblast sustaining early pregnancy.
Decidual reaction: Transformation of uterine stromal cells in response to implantation.
Q1 (2012). Cytotrophoblasts invades ?
a) Decidua parietalis
b) Decidua basalis
c) Decidua capsularis
d) None
Explanation & Answer:
Correct answer: b) Decidua basalis.
Cytotrophoblast cells proliferate and invade the decidua basalis, the maternal part beneath the implanted embryo. This invasion is critical for anchoring the placenta and remodeling maternal spiral arteries to establish adequate blood flow to the developing fetus.
Q2. The outer multinucleated trophoblast layer responsible for uterine invasion is called:
a) Cytotrophoblast
b) Syncytiotrophoblast
c) Epiblast
d) Hypoblast
Explanation & Answer:
Correct answer: b) Syncytiotrophoblast.
The syncytiotrophoblast is a multinucleated, invasive layer of trophoblast cells that erode maternal tissues during implantation and secrete human chorionic gonadotropin (hCG) to maintain pregnancy.
Q3. Which hormone is secreted by the trophoblast to maintain corpus luteum function?
a) Progesterone
b) Estrogen
c) hCG
d) Prolactin
Explanation & Answer:
Correct answer: c) hCG.
Human chorionic gonadotropin (hCG) is secreted by the syncytiotrophoblast and maintains the corpus luteum, which produces progesterone vital for sustaining the endometrium during early pregnancy.
Q4 (Clinical). Defective cytotrophoblast invasion can lead to:
a) Placenta previa
b) Ectopic pregnancy
c) Preeclampsia
d) Molar pregnancy
Explanation & Answer:
Correct answer: c) Preeclampsia.
Inadequate invasion of cytotrophoblasts into maternal spiral arteries results in poor placental perfusion, leading to preeclampsia characterized by hypertension and proteinuria in pregnancy.
Q5. The decidua capsularis is located:
a) Beneath the implanted embryo
b) Covering the embryo and enclosing the gestational sac
c) Lining the uterine cavity away from implantation site
d) Forming the maternal placenta
Explanation & Answer:
Correct answer: b) Covering the embryo and enclosing the gestational sac.
The decidua capsularis covers the implanted embryo and separates it from the uterine cavity, eventually fusing with decidua parietalis as the embryo grows.
Q6. The decidua parietalis is:
a) The decidua beneath the implanted blastocyst
b) The decidua opposite the implantation site
c) The fetal component of the placenta
d) The site of trophoblast invasion
Explanation & Answer:
Correct answer: b) The decidua opposite the implantation site.
The decidua parietalis lines the remainder of the uterine cavity away from the implantation site and eventually fuses with the decidua capsularis.
Q7 (Clinical). Which of the following cells fuse to form the syncytiotrophoblast?
a) Cytotrophoblasts
b) Epiblast cells
c) Mesodermal cells
d) Endodermal cells
Explanation & Answer:
Correct answer: a) Cytotrophoblasts.
Cytotrophoblasts proliferate and fuse to form the multinucleated syncytiotrophoblast, which invades the uterine lining during implantation.
Q8. Which of the following best describes the function of the cytotrophoblast?
a) Hormone secretion
b) Proliferative and invasive layer
c) Formation of amnion
d) Formation of yolk sac
Explanation & Answer:
Correct answer: b) Proliferative and invasive layer.
The cytotrophoblast acts as the source of cells for the expanding syncytiotrophoblast and is actively involved in invading maternal tissues during early pregnancy.
Q9. Which maternal tissue undergoes decidual reaction in response to implantation?
a) Endometrial stromal cells
b) Myometrium
c) Perimetrium
d) Ovarian stroma
Explanation & Answer:
Correct answer: a) Endometrial stromal cells.
The decidual reaction involves transformation of endometrial stromal cells into large, secretory decidual cells that support embryo implantation and placental formation.
Q10. Human chorionic gonadotropin (hCG) is detected in maternal blood by:
a) 5th day after fertilization
b) 7th-10th day after fertilization
c) 15th day after fertilization
d) 21st day after fertilization
Explanation & Answer:
Correct answer: b) 7th-10th day after fertilization.
hCG secretion by syncytiotrophoblast begins shortly after implantation, around 7-10 days post fertilization, and can be detected in maternal serum and urine to confirm pregnancy.
Subtopic: Coronary Sinus Development
Keywords & Definitions:
Coronary sinus: A large venous channel collecting blood from coronary veins and draining into the right atrium.
Truncus arteriosus: Embryonic arterial outflow tract that later divides into aorta and pulmonary artery.
Conus: Also called conus arteriosus, part of the embryonic outflow tract of the heart.
Sinus venosus: Embryonic structure receiving systemic venous blood, contributes to parts of atria and venous valves.
Atrioventricular (AV) canal: The embryonic heart canal between atria and ventricles, precursor to AV valves.
Embryonic heart: The developing heart in the fetus, undergoing morphogenesis to form adult heart structures.
Venous system: Network of veins returning deoxygenated blood to the heart.
Right atrium: Chamber of the heart receiving systemic venous blood.
Cardiac morphogenesis: Process of heart development and formation of chambers and vessels.
Endocardial cushions: Tissue masses important for septation and valve formation.
Q1 (2012). Coronary sinus develops from?
a) Truncus arteriosus
b) Conus
c) Sinus venosus
d) AV canal
Explanation & Answer:
The correct answer is c) Sinus venosus.
The coronary sinus arises from the left horn of the sinus venosus during embryonic heart development. It serves as the major venous drainage channel for the heart muscle, emptying into the right atrium. The truncus arteriosus and conus are involved in arterial outflow tract formation, while the AV canal develops into the atrioventricular valves.
Q2. The left horn of the sinus venosus forms which adult structure?
a) Coronary sinus
b) Left atrium
c) Pulmonary vein
d) Right atrium
Explanation & Answer:
The left horn of the sinus venosus develops into the coronary sinus, which collects venous blood from the heart muscle. The right horn contributes mainly to the smooth part of the right atrium.
Q3. The smooth part of the right atrium develops from:
a) Truncus arteriosus
b) Left horn of sinus venosus
c) Right horn of sinus venosus
d) AV canal
Explanation & Answer:
The smooth portion of the right atrium (sinus venarum) is derived from the right horn of the sinus venosus as it becomes incorporated into the atrial wall during development.
Q4 (Clinical). Persistent left superior vena cava draining into the coronary sinus is due to failure of regression of:
a) Left anterior cardinal vein
b) Right anterior cardinal vein
c) Sinus venosus
d) AV canal
Explanation & Answer:
Persistent left superior vena cava results from failure of the left anterior cardinal vein to regress. It typically drains into the coronary sinus, which is derived from the left horn of sinus venosus, potentially causing coronary sinus enlargement.
Q5. The atrioventricular canal contributes to:
a) Formation of AV valves
b) Formation of coronary sinus
c) Formation of pulmonary veins
d) Formation of truncus arteriosus
Explanation & Answer:
The AV canal gives rise to endocardial cushions that participate in forming the atrioventricular septum and valves, but it does not contribute to the coronary sinus.
Q6. The truncus arteriosus gives rise to:
a) Pulmonary artery and aorta
b) Coronary sinus
c) Left atrium
d) Right atrium
Explanation & Answer:
The truncus arteriosus divides into the ascending aorta and pulmonary trunk, forming the arterial outflow tracts of the heart, unrelated to venous structures like the coronary sinus.
Q7 (Clinical). An absent coronary sinus may be due to:
a) Agenesis of left horn of sinus venosus
b) Abnormal AV canal development
c) Truncus arteriosus defect
d) Conus malformation
Explanation & Answer:
Agenesis or maldevelopment of the left horn of sinus venosus can result in absent or hypoplastic coronary sinus, affecting venous drainage from the heart muscle.
Q8. The sinus venosus initially receives blood from all except:
a) Common cardinal veins
b) Umbilical veins
c) Vitelline veins
d) Pulmonary veins
Explanation & Answer:
The sinus venosus receives blood from common cardinal, vitelline, and umbilical veins, but pulmonary veins drain separately into the left atrium.
Q9. The venous valves of the heart develop from:
a) Endocardial cushions
b) Sinus venosus
c) AV canal
d) Truncus arteriosus
Explanation & Answer:
Venous valves such as the valve of the inferior vena cava develop from tissues near the sinus venosus region during cardiac development.
Q10. The conus arteriosus contributes to:
a) Right ventricular outflow tract
b) Coronary sinus
c) Left atrium
d) AV valves
Explanation & Answer:
The conus arteriosus forms the smooth part of the right ventricular outflow tract, directing blood into the pulmonary trunk.
Subtopic: Interatrial Septum Formation
Keywords & Definitions:
Fossa ovalis: Oval depression in the right atrium, remnant of fetal foramen ovale.
Septum primum: First interatrial septum growing downward during fetal heart development.
Septum secundum: Second crescent-shaped septum overlapping septum primum, forming the foramen ovale.
Ductus arteriosus: Vessel connecting pulmonary artery to aorta in fetus, bypassing lungs.
Ductus venosus: Vessel shunting blood from umbilical vein to inferior vena cava in fetus.
Foramen ovale: Opening in fetal heart allowing blood flow between atria, closes after birth.
Remnant: Vestigial structure from fetal life.
Interatrial septum: Wall between left and right atria.
Embryology: Study of prenatal development.
Patent foramen ovale (PFO): Incomplete closure of foramen ovale after birth.
Lead Question - 2012:
Fossa ovalis is a remnant of?
a) Septum primum
b) Septum secundum
c) Ductus arteriosus
d) Ductus venosus
Explanation & Answer:
The correct answer is a) Septum primum. The fossa ovalis represents the closed remnant of the foramen ovale, which is originally formed by the septum primum during fetal development. After birth, increased left atrial pressure causes fusion of septum primum and septum secundum, closing the foramen ovale and leaving the fossa ovalis.
Q2. What is the function of foramen ovale in fetal circulation?
a) Connects left and right ventricles
b) Allows blood to bypass lungs by flowing between atria
c) Connects pulmonary artery and aorta
d) Connects umbilical vein to inferior vena cava
Explanation & Answer:
Foramen ovale allows oxygenated blood to bypass the non-functioning fetal lungs by flowing directly from right atrium to left atrium, essential for fetal circulation.
Q3. Which structure closes shortly after birth due to increased left atrial pressure?
a) Foramen ovale
b) Ductus arteriosus
c) Ductus venosus
d) Umbilical vein
Explanation & Answer:
The foramen ovale closes functionally shortly after birth as increased pulmonary blood flow raises left atrial pressure, pressing septum primum against septum secundum.
Q4 (Clinical). Patent foramen ovale (PFO) may cause which clinical condition?
a) Stroke due to paradoxical embolism
b) Pulmonary hypertension
c) Aortic stenosis
d) Coarctation of aorta
Explanation & Answer:
PFO can allow venous emboli to bypass lungs and enter systemic circulation causing paradoxical embolism and ischemic stroke, especially after activities increasing right atrial pressure.
Q5. Which fetal vessel connects pulmonary artery to descending aorta?
a) Ductus arteriosus
b) Ductus venosus
c) Foramen ovale
d) Umbilical artery
Explanation & Answer:
The ductus arteriosus shunts blood from pulmonary artery to aorta, bypassing fetal lungs. It normally closes after birth to become ligamentum arteriosum.
Q6. The septum secundum forms which part of the interatrial septum?
a) Thin membranous part
b) Thick muscular ridge
c) Valve of foramen ovale
d) None of the above
Explanation & Answer:
The septum secundum is a thick muscular ridge that overlaps the foramen ovale and works with septum primum to prevent backflow after birth.
Q7. Ductus venosus connects which vessels in fetal circulation?
a) Umbilical vein to inferior vena cava
b) Pulmonary artery to aorta
c) Right atrium to left atrium
d) Umbilical artery to placenta
Explanation & Answer:
Ductus venosus bypasses the liver by connecting umbilical vein directly to the inferior vena cava, facilitating rapid oxygenated blood flow to the heart.
Q8 (Clinical). Which congenital defect results from failure of fusion of septum primum and secundum?
a) Atrial septal defect (ostium secundum type)
b) Ventricular septal defect
c) Patent ductus arteriosus
d) Tetralogy of Fallot
Explanation & Answer:
Failure of septum primum and secundum fusion causes atrial septal defect of ostium secundum type, leading to left-to-right shunt and possible right heart overload.
Q9. Which adult structure corresponds to the ductus arteriosus?
a) Ligamentum arteriosum
b) Ligamentum venosum
c) Fossa ovalis
d) Median umbilical ligament
Explanation & Answer:
After birth, the ductus arteriosus closes and becomes ligamentum arteriosum, a fibrous remnant connecting pulmonary artery and aorta.
Q10. Which statement about fetal circulation is TRUE?
a) Foramen ovale allows blood flow from left atrium to right atrium
b) Ductus arteriosus carries blood from aorta to pulmonary artery
c) Ductus venosus bypasses fetal liver
d) Umbilical arteries carry oxygenated blood
Explanation & Answer:
The ductus venosus connects the umbilical vein to inferior vena cava, allowing oxygen-rich blood to bypass the liver and enter systemic circulation rapidly.
Chapter: Embryology
Topic: Vertebral Column Development
Subtopic: Role of Notochord and Sclerotome
Keyword Definitions:
Notochord: rod-like embryonic structure inducing neural tube development and forming the nucleus pulposus.
Sclerotome: portion of somite forming vertebrae, ribs, and annulus fibrosus.
Annulus fibrosus: outer fibrous ring of the intervertebral disc.
Nucleus pulposus: gelatinous inner core of the intervertebral disc.
Neural tube: embryonic precursor to the brain and spinal cord.
Somites: segmented mesodermal blocks forming musculoskeletal structures.
Mesoderm: germ layer giving rise to muscle, bone, and connective tissues.
Vertebral arch: posterior element of vertebra enclosing the spinal cord.
Chondrification centers: initial sites of cartilage formation before ossification.
Ossification: process of bone tissue formation from cartilage or fibrous tissue.
Lead Question - 2012:
Which of the following is true about vertebral development?
a) The notochord forms the annulus fibrosus
b) The sclerotome forms the nucleus pulposus
c) The sclerotome surrounds the notochord only
d) The sclerotome surrounds the notochord and the neural tube
The correct answer is d) The sclerotome surrounds the notochord and the neural tube. In vertebral embryogenesis, sclerotome cells migrate medially to encircle both structures. The notochord persists as the nucleus pulposus, while the sclerotome forms vertebral bodies, arches, and annulus fibrosus. This organization is vital for spinal support and nerve protection.
1. Which embryonic structure forms the nucleus pulposus?
a) Notochord
b) Sclerotome
c) Dermomyotome
d) Myotome
Answer: Notochord. It persists in the adult as the gelatinous nucleus pulposus, cushioning the spine and enabling movement. Its embryonic role also includes inducing neural plate formation through signaling molecules.
2. The annulus fibrosus is derived from:
a) Notochord
b) Neural crest
c) Sclerotome
d) Endoderm
Answer: Sclerotome. Mesenchymal cells from sclerotome wrap around the notochord to form the annulus fibrosus, which supports and encloses the nucleus pulposus.
3. The myotome of the somite develops into:
a) Vertebrae
b) Skeletal muscles
c) Dermis
d) Nucleus pulposus
Answer: Skeletal muscles. The myotome gives rise to voluntary muscles of the trunk and limbs, distinct from sclerotome (bone) and dermatome (skin dermis).
4. Congenital vertebral fusion in Klippel-Feil syndrome is due to failure of:
a) Notochord segmentation
b) Sclerotome resegmentation
c) Myotome migration
d) Neural tube closure
Answer: Sclerotome resegmentation. This step allows for nerve root exit and intervertebral disc formation. Failure results in fused cervical vertebrae with limited neck motion.
5. Sclerotome differentiation is induced by signals from:
a) Neural crest
b) Ectoderm
c) Notochord and neural tube floor plate
d) Endoderm
Answer: Notochord and neural tube floor plate. They secrete Sonic hedgehog (Shh), triggering sclerotome gene expression for vertebral development.
6. First chondrification centers in vertebrae appear in:
a) Centrum and neural arches
b) Spinous process
c) Transverse process
d) Costal elements
Answer: Centrum and neural arches. These primary cartilage centers fuse later to form complete vertebrae.
7. A tumor from persistent notochordal tissue is:
a) Osteosarcoma
b) Chordoma
c) Meningioma
d) Astrocytoma
Answer: Chordoma. This slow-growing malignant tumor occurs in midline locations such as sacrum and clivus, reflecting its notochordal origin.
8. Failure of vertebral arch fusion leads to:
a) Spina bifida
b) Scoliosis
c) Kyphosis
d) Lordosis
Answer: Spina bifida. In this defect, the vertebral arch remains incomplete, potentially exposing spinal structures.
9. Vertebral column originates from which germ layer?
a) Ectoderm
b) Endoderm
c) Paraxial mesoderm
d) Intermediate mesoderm
Answer: Paraxial mesoderm. This mesoderm forms somites, which later specialize into sclerotome, myotome, and dermatome.
10. Ossification of vertebrae begins in which fetal month?
a) 1st month
b) 2nd month
c) 3rd month
d) 5th month
Answer: 3rd month. Ossification centers appear in the centrum and arches, enabling vertebral maturation before birth.
Chapter: Embryology
Topic: Development of Breast
Subtopic: Congenital Anomalies of the Mammary Gland
Keyword Definitions:
Amastia: complete absence of breast tissue and nipple.
Polymastia: presence of more than two breasts.
Polythelia: presence of additional nipples without extra breast tissue.
Mastitis: inflammation of breast tissue, usually due to infection.
Mammary ridge: embryonic thickening of ectoderm from which breasts develop.
Congenital anomaly: defect present at birth due to developmental disturbance.
Galactorrhea: inappropriate milk secretion unrelated to pregnancy.
Accessory breast tissue: extra breast tissue along the mammary line.
Hypoplasia: underdevelopment of a tissue or organ.
Neonatal mastitis: breast inflammation in newborns, often due to staphylococcal infection.
Lead Question - 2012:
Which of the following is not a congenital anomaly?
a) Amastia
b) Polymastia
c) Polythelia
d) Mastitis
The correct answer is d) Mastitis. Mastitis is an acquired inflammatory condition, most commonly due to bacterial infection during lactation. Amastia, polymastia, and polythelia result from developmental abnormalities of the mammary ridge. Mastitis can occur at any age and is not a structural defect present at birth.
1. Amastia occurs due to failure of:
a) Mammary ridge formation
b) Mammary ridge involution
c) Nipple eversion
d) Milk duct formation
Answer: Mammary ridge formation. If the mammary ridge fails to develop during embryogenesis, breast tissue and nipple are absent. This may occur unilaterally or bilaterally and can be associated with other syndromes such as ectodermal dysplasia.
2. Polymastia results from persistence of:
a) Entire mammary ridge
b) Single mammary placode
c) Accessory milk ducts
d) Nipple-areola complex
Answer: Entire mammary ridge. Normally, the mammary ridge regresses except at the site of future breasts. Failure of regression in other areas leads to accessory breasts.
3. Which is the most common congenital breast anomaly?
a) Amastia
b) Polymastia
c) Polythelia
d) Hypoplasia
Answer: Polythelia. Extra nipples without associated glandular tissue are the most frequent anomaly. They often occur along the “milk line” and are usually asymptomatic.
4. In which syndrome is amastia commonly seen?
a) Poland syndrome
b) Turner syndrome
c) Klinefelter syndrome
d) Marfan syndrome
Answer: Poland syndrome. This rare congenital condition involves unilateral chest wall and breast muscle hypoplasia or absence, sometimes associated with amastia.
5. Mastitis is most common in which period?
a) Neonatal
b) Puberty
c) Lactational
d) Post-menopause
Answer: Lactational. Cracks in the nipple during breastfeeding allow bacterial entry, leading to inflammation and infection, usually by Staphylococcus aureus.
6. Which breast condition can present as a midline chest wall swelling at birth?
a) Polymastia
b) Polythelia
c) Amastia
d) Mastitis neonatorum
Answer: Mastitis neonatorum. Caused by maternal hormones crossing the placenta, it can result in breast enlargement and sometimes infection in newborns.
7. Polythelia may be mistaken for:
a) Lipoma
b) Mole
c) Sebaceous cyst
d) All of the above
Answer: All of the above. Supernumerary nipples can be small, pigmented, and mistaken for skin lesions; histology confirms nipple structures.
8. Breast tissue along the axilla is usually due to:
a) Polymastia
b) Lymphadenopathy
c) Fibroadenoma
d) Fat necrosis
Answer: Polymastia. Accessory breast tissue can develop in the axilla and respond to hormonal changes during puberty and pregnancy.
9. Which hormone stimulates breast development during puberty?
a) Estrogen
b) Progesterone
c) Prolactin
d) Oxytocin
Answer: Estrogen. It stimulates ductal growth, while progesterone promotes lobuloalveolar development. Both act synergistically for breast maturation.
10. Which congenital breast anomaly is associated with urinary tract malformations?
a) Polythelia
b) Amastia
c) Polymastia
d) Hypoplasia
Answer: Polythelia. Embryologically, mammary and urinary systems may share developmental signaling pathways; polythelia has been linked to renal anomalies in some cases.
Chapter: Embryology
Topic: Development of Gastrointestinal Tract
Subtopic: Development of Rectum and Anal Canal
Keyword Definitions:
Rectum: terminal part of the large intestine between sigmoid colon and anal canal.
Cloaca: common cavity in embryo for urinary, genital, and digestive tracts.
Hindgut: posterior portion of primitive gut tube giving rise to distal colon and rectum.
Allantois: embryonic diverticulum involved in early urine collection.
Urogenital sinus: embryonic structure that develops into urinary bladder and urethra.
Anal canal: terminal part of digestive tract distal to rectum.
Proctodeum: ectodermal depression forming lower anal canal.
Pectinate line: junction between endodermal and ectodermal anal canal.
Imperforate anus: congenital absence of anal opening.
Cloacal membrane: embryonic membrane separating cloaca from exterior.
Lead Question - 2012:
Rectum develops from
a) Cloaca
b) Hind gut
c) Allantoic remnants
d) Urogenital sinus
The correct answer is b) Hind gut. The rectum develops from the endodermal hindgut. During embryogenesis, the cloaca divides into the urogenital sinus and the anorectal canal by the urorectal septum. The upper anal canal and rectum are derived from hindgut, whereas lower anal canal is from ectodermal proctodeum.
1. The cloaca is divided into the urogenital sinus and anorectal canal by:
a) Cloacal membrane
b) Urorectal septum
c) Pectinate line
d) Allantoic duct
Answer: Urorectal septum. It is a mesodermal structure that grows to separate the cloaca into the anterior urogenital sinus and posterior anorectal canal, preventing communication between urinary and digestive tracts in normal development.
2. The lower anal canal develops from:
a) Hindgut
b) Cloaca
c) Proctodeum
d) Allantois
Answer: Proctodeum. The lower one-third of the anal canal originates from the ectodermal proctodeum, which invaginates to meet the endodermal upper canal at the pectinate line.
3. Which embryonic germ layer forms the epithelium of the rectum?
a) Mesoderm
b) Endoderm
c) Ectoderm
d) Neural crest
Answer: Endoderm. The lining epithelium of the rectum and most of the anal canal above the pectinate line arises from the endoderm of the hindgut.
4. A newborn with imperforate anus likely has failure of:
a) Cloacal membrane rupture
b) Pectinate line formation
c) Proctodeum invagination
d) Hindgut rotation
Answer: Cloacal membrane rupture. Normally, the cloacal membrane degenerates to create an opening; persistence leads to imperforate anus, often associated with other anomalies.
5. Hirschsprung’s disease results from failure of migration of:
a) Mesodermal cells
b) Neural crest cells
c) Endodermal epithelium
d) Myoblasts
Answer: Neural crest cells. Absence of ganglion cells in the distal colon leads to functional obstruction due to failure of peristalsis.
6. Which structure marks the junction of endodermal and ectodermal parts of the anal canal?
a) Dentate line
b) Pectinate line
c) Anocutaneous line
d) Anal verge
Answer: Pectinate line. This line is important for differences in blood supply, innervation, and lymphatic drainage between upper and lower anal canal.
7. Which artery supplies the upper rectum?
a) Superior rectal artery
b) Middle rectal artery
c) Inferior rectal artery
d) Internal pudendal artery
Answer: Superior rectal artery. It is a continuation of the inferior mesenteric artery and supplies the rectum above the pectinate line.
8. The anorectal canal is lined by:
a) Simple squamous epithelium
b) Columnar epithelium above, stratified squamous below
c) Transitional epithelium
d) Pseudostratified ciliated columnar
Answer: Columnar epithelium above, stratified squamous below. This change occurs at the pectinate line, correlating with embryonic origin.
9. Which venous drainage is associated with internal hemorrhoids?
a) Inferior rectal vein
b) Middle rectal vein
c) Superior rectal vein
d) External pudendal vein
Answer: Superior rectal vein. It drains into the portal system, and its dilatation above the pectinate line causes internal hemorrhoids.
10. The urogenital sinus gives rise to all except:
a) Urinary bladder
b) Urethra
c) Lower anal canal
d) Prostate
Answer: Lower anal canal. This structure arises from the proctodeum, not the urogenital sinus. The urogenital sinus forms urinary and part of reproductive structures.
Chapter: Embryology
Topic: Pharyngeal Arches
Subtopic: Skeletal Derivatives of Pharyngeal Arches
Keyword Definitions:
Pharyngeal arches: Mesodermal and neural crest cell-derived structures in the embryonic head and neck region.
Second pharyngeal arch: Also called the hyoid arch, contributes to parts of the hyoid bone, stapes, and facial muscles.
Malleus: Middle ear ossicle derived from the first pharyngeal arch.
Incus: Middle ear ossicle derived from the first pharyngeal arch.
Stapes: Middle ear ossicle partly derived from the second pharyngeal arch.
Maxilla: Upper jaw bone derived from the first pharyngeal arch.
Reichert’s cartilage: Cartilage of the second arch forming specific skeletal elements.
Hyoid bone: Bone in the neck supporting the tongue and swallowing muscles.
Facial nerve (CN VII): Nerve of the second pharyngeal arch, supplying facial muscles.
Styloid process: Bony projection from temporal bone derived from the second pharyngeal arch.
Lead Question - 2012:
Skeletal derivative of 2nd pharyngeal arch -
a) Malleus
b) Incus
c) Stapes
d) Maxilla
The correct answer is c) Stapes. The second pharyngeal arch, also known as the hyoid arch, contains Reichert’s cartilage. It forms the stapes of the middle ear, styloid process of the temporal bone, stylohyoid ligament, and parts of the hyoid bone (lesser horn and upper body). Malleus and incus are first arch derivatives.
1. The nerve associated with the second pharyngeal arch is:
a) Trigeminal nerve
b) Facial nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Answer: Facial nerve. The second arch is innervated by cranial nerve VII, responsible for motor supply to muscles of facial expression and taste from the anterior two-thirds of the tongue via the chorda tympani.
2. Reichert’s cartilage develops from which pharyngeal arch?
a) First
b) Second
c) Third
d) Fourth
Answer: Second. Reichert’s cartilage gives rise to several skeletal derivatives including stapes, styloid process, and part of the hyoid bone, highlighting the role of the second pharyngeal arch in craniofacial development.
3. The lesser horn of the hyoid bone is derived from:
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Answer: Second arch. The lesser horn and upper part of the body of the hyoid bone are derivatives of Reichert’s cartilage from the second pharyngeal arch.
4. Which arch anomaly is associated with congenital stapes fixation?
a) First
b) Second
c) Third
d) Fourth
Answer: Second arch. Abnormal development of Reichert’s cartilage can lead to stapes fixation, resulting in conductive hearing loss.
5. Which muscle group arises from the second pharyngeal arch?
a) Muscles of mastication
b) Muscles of facial expression
c) Pharyngeal constrictors
d) Intrinsic tongue muscles
Answer: Muscles of facial expression. The second arch forms muscles for facial expressions, stapedius, stylohyoid, and posterior belly of the digastric.
6. The stapes footplate is related embryologically to:
a) First arch mesoderm
b) Second arch cartilage
c) Otic capsule
d) Nasal capsule
Answer: Otic capsule. While the stapes suprastructure comes from the second arch, the footplate originates from the otic capsule surrounding the developing inner ear.
7. Which pharyngeal arch abnormality can cause microtia with middle ear anomalies?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Answer: Second arch. Malformations can affect auricular hillocks (external ear) and ossicles like stapes, causing hearing defects.
8. The stylohyoid ligament develops from:
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Answer: Second arch. The stylohyoid ligament is derived from Reichert’s cartilage, which also forms the styloid process and parts of the hyoid bone.
9. Which cranial nerve is affected in Bell’s palsy, a condition involving muscles of facial expression?
a) CN V
b) CN VII
c) CN IX
d) CN X
Answer: CN VII (Facial nerve). Bell’s palsy is a lower motor neuron lesion affecting the nerve of the second arch, leading to unilateral facial muscle weakness.
10. In development, the second pharyngeal arch overgrows the third and fourth arches to form:
a) Cervical sinus
b) External auditory canal
c) Submandibular gland
d) Carotid sheath
Answer: Cervical sinus. This overgrowth creates a temporary space that normally disappears; persistence can cause branchial cleft cysts.
Chapter: Embryology
Topic: Germ Layer Derivatives
Subtopic: Ectoderm, Mesoderm, and Endoderm Origins
Keyword Definitions:
Ectoderm: The outermost germ layer forming skin, nervous system, and certain sensory organs.
Endoderm: The innermost germ layer forming gastrointestinal tract lining and respiratory epithelium.
Mesoderm: The middle germ layer forming muscles, bones, blood vessels, and connective tissues.
Hypophysis (pituitary gland): Formed partly from ectoderm (Rathke’s pouch) and partly from neuroectoderm.
Retina: Derived from neuroectoderm of the forebrain.
Spinal cord: Derived from neuroectoderm.
Adrenal cortex: Derived from mesoderm, specifically intermediate mesoderm.
Neural crest cells: Specialized ectodermal cells giving rise to diverse structures including melanocytes and adrenal medulla.
Surface ectoderm: Ectoderm forming epidermis, hair, nails, and glands of the skin.
Neuroectoderm: Specialized ectoderm forming the brain, spinal cord, and retina.
Lead Question - 2012:
All are derived from ectoderm except -
a) Hypophysis
b) Retina
c) Spinal cord
d) Adrenal cortex
The correct answer is d) Adrenal cortex. The adrenal cortex is derived from mesoderm, while the adrenal medulla comes from neural crest cells (ectoderm). Hypophysis, retina, and spinal cord are all ectodermal derivatives, specifically neuroectoderm or surface ectoderm in the case of Rathke’s pouch. This distinction is key in embryology MCQs.
1. The adrenal medulla is derived from:
a) Surface ectoderm
b) Neuroectoderm
c) Neural crest cells
d) Mesoderm
Answer: Neural crest cells. The medulla’s chromaffin cells originate from neural crest ectoderm, explaining their neuroendocrine function in secreting catecholamines like epinephrine and norepinephrine.
2. Rathke’s pouch gives rise to which structure?
a) Neurohypophysis
b) Adenohypophysis
c) Pineal gland
d) Retina
Answer: Adenohypophysis. Rathke’s pouch is an ectodermal outgrowth from the roof of the mouth, forming the anterior pituitary, which secretes hormones like GH, ACTH, and prolactin.
3. Which germ layer forms the lens of the eye?
a) Surface ectoderm
b) Neuroectoderm
c) Mesoderm
d) Endoderm
Answer: Surface ectoderm. The lens develops from a placode of surface ectoderm induced by the optic vesicle derived from neuroectoderm.
4. Which of the following is a mesodermal derivative?
a) Retina
b) Dermis of skin
c) Epidermis of skin
d) Anterior pituitary
Answer: Dermis of skin. While epidermis is from ectoderm, dermis is largely mesodermal in origin except in certain craniofacial regions.
5. Which embryonic layer forms the thyroid follicular cells?
a) Ectoderm
b) Endoderm
c) Mesoderm
d) Neural crest cells
Answer: Endoderm. Follicular cells derive from endodermal epithelium of the pharyngeal floor, while parafollicular cells come from neural crest cells.
6. Melanocytes originate from:
a) Surface ectoderm
b) Mesoderm
c) Neural crest cells
d) Endoderm
Answer: Neural crest cells. Melanocytes are pigment-producing cells found in the skin, hair, and eyes, and their origin explains disorders like vitiligo.
7. A newborn presents with aniridia (absence of iris). This defect most likely involves which embryonic derivative?
a) Neuroectoderm
b) Surface ectoderm
c) Mesoderm
d) Endoderm
Answer: Neuroectoderm. The iris stroma is mesodermal, but the iris epithelium and muscles are from neuroectoderm, explaining the visual defect.
8. The spinal cord originates from:
a) Surface ectoderm
b) Neuroectoderm
c) Mesoderm
d) Endoderm
Answer: Neuroectoderm. It forms from the neural tube, which develops from ectoderm after neural plate folding during neurulation.
9. The epithelial lining of the respiratory tract is derived from:
a) Surface ectoderm
b) Neuroectoderm
c) Endoderm
d) Mesoderm
Answer: Endoderm. Endoderm forms the epithelium of the respiratory and gastrointestinal tracts, while mesoderm forms their connective and muscular tissues.
10. Which embryonic origin best explains congenital absence of sweat glands (anhidrosis)?
a) Mesoderm
b) Surface ectoderm
c) Neuroectoderm
d) Endoderm
Answer: Surface ectoderm. Sweat glands are epidermal derivatives, and ectodermal dysplasia can lead to absence or dysfunction of these glands.
Chapter: Embryology
Topic: Development of External Genitalia
Subtopic: Female External Genitalia Derivatives
Keyword Definitions:
Labia majora: Paired folds of skin in the female external genitalia derived from genital swellings.
Urogenital sinus: Endodermal structure forming parts of the urethra, vagina, and vestibule.
Müllerian duct: Paramesonephric duct forming uterus, fallopian tubes, and upper vagina.
Genital ridge: Mesodermal structure giving rise to gonads.
Genital swelling: Embryonic structure forming labia majora in females and scrotum in males.
Labia minora: Derived from genital folds (urogenital folds).
Clitoris: Derived from genital tubercle.
Hypospadias: Urethral opening defect due to incomplete fusion of urogenital folds in males.
Neuroectoderm: Specialized ectoderm forming CNS structures.
Mesoderm: Middle germ layer forming muscles, connective tissue, and some reproductive structures.
Lead Question - 2012:
Development of labia majora is from -
a) Urogenital sinus
b) Mullerian duct
c) Genital ridge
d) Genital swelling
The correct answer is d) Genital swelling. In females, genital swellings enlarge and form the labia majora. In males, these swellings fuse in the midline to form the scrotum. This is an important embryological distinction when differentiating homologous male and female structures in developmental anatomy.
1. Labia minora are derived from:
a) Genital tubercle
b) Genital folds
c) Genital swelling
d) Urogenital sinus
Answer: Genital folds. The urogenital folds in females persist as the labia minora, while in males they fuse to form the penile urethra. This is a classic example of sexual homology in embryology.
2. The clitoris develops from:
a) Genital folds
b) Genital swelling
c) Genital tubercle
d) Urogenital sinus
Answer: Genital tubercle. The genital tubercle elongates to form the clitoris in females and the penis in males. Its growth is influenced by sex hormones during development.
3. The male homolog of the labia majora is:
a) Penis
b) Scrotum
c) Urethra
d) Glans penis
Answer: Scrotum. Genital swellings fuse in males to form the scrotum, making it the male counterpart of the labia majora in females.
4. Which structure arises from the urogenital sinus in females?
a) Clitoris
b) Lower vagina
c) Labia majora
d) Mons pubis
Answer: Lower vagina. The lower one-third of the vagina develops from the endodermal urogenital sinus, while the upper two-thirds come from the Müllerian ducts.
5. A newborn female presents with fused labia majora. This condition is likely due to:
a) Excess estrogen exposure
b) Androgen excess in utero
c) Müllerian agenesis
d) Gonadal dysgenesis
Answer: Androgen excess in utero. Virilization due to congenital adrenal hyperplasia can cause fusion of labia majora and other masculinization features.
6. Which embryonic structure forms the mons pubis?
a) Genital swelling
b) Genital folds
c) Genital tubercle
d) Urogenital sinus
Answer: Genital swelling. Along with forming the labia majora, genital swellings contribute to the development of the mons pubis in females.
7. The male homolog of the clitoris is:
a) Glans penis
b) Corpus spongiosum
c) Urethra
d) Scrotum
Answer: Glans penis. Both glans penis and clitoris originate from the genital tubercle, highlighting their homologous nature.
8. Which germ layer primarily contributes to the genital swellings?
a) Endoderm
b) Ectoderm
c) Mesoderm
d) Neural crest cells
Answer: Mesoderm. External genitalia structures like genital swellings are mesodermal in origin, with surface ectoderm covering.
9. A 46,XY DSD newborn has bifid scrotum resembling labia majora. This is due to:
a) Müllerian agenesis
b) Incomplete fusion of genital swellings
c) Failure of genital tubercle elongation
d) Cloacal membrane persistence
Answer: Incomplete fusion of genital swellings. In males, unfused genital swellings result in bifid scrotum, resembling female labia majora.
10. In androgen insensitivity syndrome (AIS), the labia majora develop from:
a) Müllerian ducts
b) Urogenital folds
c) Genital swellings
d) Genital tubercle
Answer: Genital swellings. Even in AIS where testes are present, external genitalia develop along the female pathway, with labia majora from genital swellings.
Chapter: Embryology
Topic: Early Development
Subtopic: Implantation and Blastocyst Formation
Keyword Definitions:
Blastocyst: Stage of embryonic development after morula, with an inner cell mass and a fluid-filled cavity (blastocoel).
Endometrium: Inner lining of the uterus, prepared for implantation under progesterone influence.
Implantation: Process of embedding the blastocyst into the endometrial lining.
Trophoblast: Outer cell layer of the blastocyst that forms placenta components.
Zona pellucida: Glycoprotein coat surrounding the early embryo, shed before implantation.
Morula: Solid ball of cells formed after cleavage of the zygote.
Hatching: Process by which the blastocyst emerges from the zona pellucida.
Syncytiotrophoblast: Multinucleated trophoblast cells invading the endometrium.
Cytotrophoblast: Inner trophoblast layer with mitotic activity.
Luteal phase: Phase of menstrual cycle dominated by progesterone secretion.
Lead Question - 2012:
Blastocyst makes contact with endometrium on ?
a) < 3 days
b) 5 - 7 days
c) 8 - 11 days
d) 15 -16 days
The correct answer is b) 5 - 7 days. The blastocyst reaches the uterine cavity around day 5 after fertilization and begins attaching to the endometrial epithelium between days 5 and 7. This timing ensures optimal endometrial receptivity, which is hormonally regulated, primarily by progesterone from the corpus luteum.
1. The zona pellucida disappears during which stage?
a) Zygote
b) Morula
c) Early blastocyst
d) Late blastocyst
Answer: Early blastocyst. Hatching occurs when the blastocyst breaks free from the zona pellucida around day 5, enabling direct contact with the endometrium for implantation.
2. Which layer of the trophoblast invades the endometrium?
a) Cytotrophoblast
b) Syncytiotrophoblast
c) Hypoblast
d) Epiblast
Answer: Syncytiotrophoblast. This multinucleated layer secretes enzymes and hCG, aiding in embedding the embryo into maternal tissue.
3. Clinical: A woman undergoes IVF and embryo transfer. The best day for transfer to mimic natural implantation is:
a) Day 2
b) Day 3
c) Day 5
d) Day 10
Answer: Day 5. A day-5 blastocyst transfer aligns with the natural implantation window, increasing pregnancy rates.
4. The inner cell mass of the blastocyst forms:
a) Placenta
b) Amniotic sac only
c) Embryo proper
d) Decidua basalis
Answer: Embryo proper. The inner cell mass differentiates into epiblast and hypoblast, forming all embryonic tissues.
5. Which hormone maintains endometrial receptivity for implantation?
a) Estrogen
b) Progesterone
c) LH
d) FSH
Answer: Progesterone. Secreted by the corpus luteum, it converts the endometrium to a secretory phase, crucial for implantation.
6. The decidua basalis develops from:
a) Embryonic mesoderm
b) Maternal endometrium
c) Chorionic villi
d) Cytotrophoblast
Answer: Maternal endometrium. The decidua basalis is the maternal portion of the placenta, forming at the site of implantation.
7. Clinical: An ectopic pregnancy in the fallopian tube occurs because implantation happens:
a) Too early
b) Too late
c) Before blastocyst reaches uterus
d) After corpus luteum regression
Answer: Before blastocyst reaches uterus. If zona pellucida sheds prematurely, implantation can occur in abnormal sites like the fallopian tube.
8. Which of the following occurs last in early embryonic development?
a) Cleavage
b) Morula formation
c) Blastocyst formation
d) Implantation
Answer: Implantation. Cleavage → morula → blastocyst → implantation is the correct sequence.
9. The blastocoel is:
a) Space between amnion and chorion
b) Cavity within blastocyst
c) Fluid-filled yolk sac
d) Maternal blood-filled lacuna
Answer: Cavity within blastocyst. It helps separate the inner cell mass from the trophoblast layer.
10. Clinical: Which marker confirms trophoblastic activity soon after implantation?
a) Progesterone
b) Estrogen
c) hCG
d) Inhibin B
Answer: hCG. Secreted by syncytiotrophoblast cells, detectable in maternal blood within days after implantation.