Embryology

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.

Chapter: Embryology

Topic: Early Embryonic Development

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

Chapter: Embryology

Topic: Development of Pharyngeal Arches

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.

Chapter: Embryology

Topic: Neuroglial Cells

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.

Chapter: Embryology

Topic: Development of Interatrial Septum

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.

Chapter: Embryology

Topic: Germ Layer Derivatives

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.

Chapter: Embryology

Topic: Germ Layer Derivatives

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.

Chapter: Embryology

Topic: Body Cavities

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.

Chapter: Embyology

Topic: Trophoblast

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.

Chapter: Embryology

Topic: Venous System Formation

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.

Chapter: Cardiovascular System

Topic: Embryology of Heart

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