Chapter: Embryology; Topic: Cell Division; Subtopic: Meiotic Prophase I – Stages and Significance
Key Definitions:
• Meiosis: A specialized form of cell division that reduces the chromosome number by half, producing haploid gametes.
• Prophase I: The first and longest stage of meiosis I, during which homologous chromosomes pair and exchange genetic material through crossing over.
• Synapsis: The pairing of homologous chromosomes during zygotene stage of prophase I.
• Crossing over: Exchange of genetic material between non-sister chromatids of homologous chromosomes during pachytene, leading to genetic variation.
Lead Question (NEET PG 2015):
1. Which is not a stage of prophase?
a) Diakinesis
b) Leptotene
c) Zygotene
d) Arachytene
Answer: d) Arachytene
Explanation: Prophase I of meiosis is divided into five distinct stages — leptotene, zygotene, pachytene, diplotene, and diakinesis. Each stage has unique events: pairing of homologous chromosomes, synapsis, and crossing over occur sequentially. The term “Arachytene” is incorrect and does not exist as a recognized substage of prophase I. During this prolonged phase, the genetic material undergoes condensation, recombination, and preparation for segregation. This stage is crucial for ensuring genetic variability and accurate chromosome segregation during gametogenesis.
Guessed Questions (Related to Meiotic Prophase I and Cell Division):
2. Crossing over occurs during which stage of prophase I?
a) Leptotene
b) Zygotene
c) Pachytene
d) Diplotene
Answer: c) Pachytene
Explanation: Crossing over occurs during pachytene, where homologous chromosomes exchange genetic material between non-sister chromatids at chiasmata. This process contributes to genetic diversity among gametes and is mediated by the enzyme recombinase.
3. Synapsis or pairing of homologous chromosomes occurs during:
a) Leptotene
b) Zygotene
c) Diplotene
d) Metaphase
Answer: b) Zygotene
Explanation: During zygotene, homologous chromosomes begin to pair along their lengths through a protein structure called the synaptonemal complex. This pairing is essential for crossing over in the next stage, pachytene.
4. Clinical: Nondisjunction leading to Down syndrome usually occurs during:
a) Prophase I
b) Metaphase I
c) Anaphase I
d) Telophase I
Answer: c) Anaphase I
Explanation: Nondisjunction, the failure of homologous chromosomes to separate properly, occurs during anaphase I of meiosis. This results in aneuploidy, such as trisomy 21 (Down syndrome), when a gamete with an extra chromosome fuses during fertilization.
5. Diplotene stage of prophase I is characterized by:
a) Disappearance of chiasmata
b) Terminalization of chiasmata
c) Separation of homologous chromosomes except at chiasmata
d) Formation of spindle fibers
Answer: c) Separation of homologous chromosomes except at chiasmata
Explanation: In the diplotene stage, homologous chromosomes begin to separate but remain attached at chiasmata — the sites of crossing over. This stage may be prolonged, especially in oocytes, where it can last until puberty.
6. Clinical: Arrest of oocytes in females occurs at which stage of meiosis?
a) Pachytene
b) Diplotene
c) Diakinesis
d) Anaphase I
Answer: b) Diplotene
Explanation: Primary oocytes in females remain arrested in diplotene stage of prophase I from fetal life until puberty. Meiosis resumes during each menstrual cycle after hormonal stimulation by LH.
7. The disappearance of the nuclear membrane and nucleolus occurs during which substage of prophase I?
a) Pachytene
b) Diplotene
c) Diakinesis
d) Leptotene
Answer: c) Diakinesis
Explanation: Diakinesis is the final stage of prophase I, marked by maximal chromosome condensation and disappearance of the nuclear membrane and nucleolus. The spindle apparatus begins to form, preparing for metaphase I alignment.
8. Clinical: A woman’s oocytes remaining arrested for decades may accumulate DNA damage. This increases risk of:
a) Monosomy
b) Polyploidy
c) Aneuploidy
d) Triploidy
Answer: c) Aneuploidy
Explanation: Oocytes arrested in diplotene for prolonged periods are prone to errors during chromosome segregation when meiosis resumes, leading to aneuploidy (e.g., trisomy 21, 18, 13). This risk increases with maternal age.
9. The synaptonemal complex first appears during:
a) Leptotene
b) Zygotene
c) Pachytene
d) Diakinesis
Answer: b) Zygotene
Explanation: The synaptonemal complex, a tripartite protein structure, forms during zygotene and facilitates homologous chromosome pairing and recombination during pachytene.
10. Clinical: A 40-year-old woman gives birth to a baby with trisomy 21. The error most likely occurred during:
a) Maternal meiosis I
b) Maternal meiosis II
c) Spermatogenesis
d) Zygotic mitosis
Answer: a) Maternal meiosis I
Explanation: In most cases of Down syndrome, nondisjunction occurs during maternal meiosis I due to aging oocytes and improper homologous chromosome separation during prophase I and anaphase I.
11. During which meiotic stage does chromosomal recombination (genetic exchange) take place?
a) Leptotene
b) Zygotene
c) Pachytene
d) Diplotene
Answer: c) Pachytene
Explanation: Chromosomal recombination occurs during pachytene as homologous chromosomes exchange segments of genetic material at chiasmata. This ensures genetic diversity among gametes, a fundamental outcome of meiosis.
Chapter: Embryology; Topic: Cardiovascular System; Subtopic: Development of Interatrial Septum
Key Definitions:
• Fossa ovalis: A depression in the interatrial septum of the adult heart, representing the closed foramen ovale of the fetal heart.
• Foramen ovale: An opening in the fetal interatrial septum that allows blood to pass from the right atrium to the left atrium, bypassing the nonfunctional fetal lungs.
• Septum primum: The first septum to develop in the atrium, forming the floor of the fossa ovalis in adults.
• Septum secundum: A muscular septum that grows to the right of septum primum and forms the foramen ovale margin.
Lead Question (NEET PG 2015):
1. Fossa ovalis is a remnant of:
a) Septum primum
b) Septum secundum
c) Septum spurium
d) AV cushion
Answer: a) Septum primum
Explanation: The fossa ovalis, located in the interatrial septum, is the remnant of the foramen ovale which closes after birth. The foramen ovale is formed between the septum primum and septum secundum in the fetus, allowing right-to-left shunting of oxygenated blood. After birth, when pulmonary circulation begins, increased left atrial pressure closes the foramen ovale functionally, and later anatomically, leaving the fossa ovalis as a depression. The floor of the fossa ovalis represents the septum primum, while the upper ridge (limbus fossa ovalis) corresponds to the septum secundum.
Guessed Questions (Related to Fetal Circulation and Atrial Septum):
2. The foramen ovale in fetal life allows blood to flow from:
a) Left atrium to right atrium
b) Right atrium to left atrium
c) Right ventricle to left atrium
d) Pulmonary artery to aorta
Answer: b) Right atrium to left atrium
Explanation: The foramen ovale shunts oxygenated blood from the right atrium to the left atrium, bypassing the fetal lungs which are nonfunctional before birth. This ensures oxygen-rich blood from the placenta reaches systemic circulation efficiently.
3. Closure of foramen ovale after birth occurs primarily due to:
a) Decrease in right atrial pressure
b) Increase in right atrial pressure
c) Increase in right ventricular pressure
d) Increase in pulmonary resistance
Answer: a) Decrease in right atrial pressure
Explanation: After birth, the first breath expands the lungs, decreasing pulmonary resistance and right atrial pressure while increasing left atrial pressure. This pressure difference forces the septum primum against the septum secundum, closing the foramen ovale.
4. Clinical: A patent foramen ovale may lead to which condition?
a) Left-to-right shunt
b) Right-to-left shunt
c) Cyanosis
d) Both b and c
Answer: d) Both b and c
Explanation: A patent foramen ovale allows right-to-left shunting of blood, especially during conditions increasing right atrial pressure. This can cause deoxygenated blood to enter systemic circulation, leading to cyanosis and paradoxical embolism.
5. The limbus fossa ovalis is derived from:
a) Septum primum
b) Septum secundum
c) AV cushion
d) Sinus venosus
Answer: b) Septum secundum
Explanation: The limbus fossa ovalis, a prominent margin around the fossa ovalis, is derived from the septum secundum. It forms the upper boundary of the fossa and ensures one-way flow of blood during fetal life.
6. Clinical: Failure of the foramen ovale to close after birth results in:
a) Tetralogy of Fallot
b) Patent foramen ovale
c) Transposition of great arteries
d) Aortic stenosis
Answer: b) Patent foramen ovale
Explanation: A patent foramen ovale (PFO) is caused by incomplete fusion of the septum primum and septum secundum. It is present in about 25% of adults and may lead to paradoxical emboli or transient ischemic attacks.
7. The interatrial septum develops from:
a) Septum primum and septum secundum
b) Septum spurium and AV cushion
c) Endocardial cushions only
d) Sinus venosus and truncus arteriosus
Answer: a) Septum primum and septum secundum
Explanation: The interatrial septum forms from two overlapping septa — septum primum (thin, membranous) and septum secundum (thick, muscular). Their interaction forms the foramen ovale, essential for fetal circulation.
8. Clinical: In fetal echocardiography, persistence of blood flow through the foramen ovale after birth indicates:
a) Congenital heart block
b) Patent foramen ovale
c) Pulmonary hypertension
d) Double outlet right ventricle
Answer: b) Patent foramen ovale
Explanation: Persistent flow through the foramen ovale after birth suggests incomplete closure, diagnosed as patent foramen ovale. It can predispose to paradoxical embolism where venous emboli pass into systemic circulation.
9. The septum spurium contributes to formation of which cardiac structure?
a) Right atrium roof
b) Left atrium floor
c) Coronary sinus
d) Fossa ovalis
Answer: a) Right atrium roof
Explanation: The septum spurium forms part of the roof of the right atrium by fusion of the right and left venous valves of the sinus venosus, but does not contribute directly to the interatrial septum.
10. Clinical: A patient with patent foramen ovale experiences a stroke following deep vein thrombosis. This is due to:
a) Pulmonary embolism
b) Paradoxical embolism
c) Coronary thrombosis
d) Cerebral aneurysm
Answer: b) Paradoxical embolism
Explanation: A paradoxical embolism occurs when a thrombus passes from the right to the left atrium via a patent foramen ovale, bypassing the lungs and entering systemic circulation, potentially causing a stroke.
11. The functional closure of the foramen ovale occurs:
a) Immediately after birth
b) After one week
c) After one month
d) During fetal life
Answer: a) Immediately after birth
Explanation: Functional closure of the foramen ovale occurs immediately after birth due to increased left atrial pressure as pulmonary circulation begins. Anatomical fusion of septa occurs later, usually within the first year of life, forming the fossa ovalis.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Development of Nephrons and Collecting System
Key Definitions:
• Nephron: The functional unit of the kidney, responsible for filtration, reabsorption, and secretion, composed of the glomerulus, tubules, and loop of Henle.
• Metanephros: The definitive kidney formed from the interaction between the ureteric bud and metanephric mesenchyme.
• Ureteric bud: An outgrowth from the mesonephric duct that gives rise to the ureter, renal pelvis, calyces, and collecting ducts.
• Mesonephros: A transient, intermediate kidney structure that functions temporarily during early embryonic life before the metanephros develops.
Lead Question (NEET PG 2015):
1. Nephron is derived from:
a) Ureteric bud
b) Mesonephric duct
c) Metanephros
d) Mesonephros
Answer: c) Metanephros
Explanation: The nephron, the functional unit of the kidney, develops from the metanephric blastema (metanephric mesenchyme), which arises from the intermediate mesoderm. The metanephric mesenchyme interacts with the ureteric bud to form nephrons, including the glomerulus, proximal tubule, loop of Henle, and distal convoluted tubule. The ureteric bud, on the other hand, forms the collecting system (collecting ducts, calyces, renal pelvis, and ureter). This reciprocal induction between the metanephric blastema and ureteric bud ensures proper nephron differentiation and renal development.
Guessed Questions (Related to Development of Urinary System):
2. The ureteric bud gives rise to all of the following except:
a) Collecting ducts
b) Renal pelvis
c) Loop of Henle
d) Ureter
Answer: c) Loop of Henle
Explanation: The loop of Henle develops from the metanephric mesenchyme, not the ureteric bud. The ureteric bud forms the collecting ducts, calyces, renal pelvis, and ureter, representing the collecting system of the kidney.
3. Clinical: A newborn presents with unilateral renal agenesis. The most likely embryological defect is:
a) Failure of metanephric blastema formation
b) Failure of ureteric bud formation
c) Failure of mesonephric duct development
d) Failure of pronephros formation
Answer: b) Failure of ureteric bud formation
Explanation: Unilateral renal agenesis occurs when the ureteric bud fails to develop or fails to contact the metanephric mesenchyme. As a result, nephron induction does not occur, leading to absence of one kidney.
4. The glomerulus and Bowman’s capsule are derived from:
a) Ureteric bud
b) Metanephric mesenchyme
c) Mesonephric duct
d) Cloaca
Answer: b) Metanephric mesenchyme
Explanation: Both the glomerulus and Bowman’s capsule originate from the metanephric mesenchyme, part of the metanephros. These structures form the filtration barrier crucial for renal function.
5. Clinical: Bilateral renal agenesis leads to which fetal condition?
a) Anencephaly
b) Oligohydramnios
c) Polyhydramnios
d) Hydrocephalus
Answer: b) Oligohydramnios
Explanation: Bilateral renal agenesis results in absence of urine formation, leading to oligohydramnios (reduced amniotic fluid). This causes pulmonary hypoplasia, limb deformities, and facial anomalies, collectively known as Potter sequence.
6. The collecting ducts of the kidney develop from:
a) Metanephric mesenchyme
b) Ureteric bud
c) Mesonephric duct
d) Intermediate mesoderm directly
Answer: b) Ureteric bud
Explanation: The collecting ducts originate from branching of the ureteric bud, which is an outgrowth of the mesonephric duct. This structure ultimately gives rise to the entire collecting system of the kidney.
7. Clinical: A cystic kidney in a newborn is caused by abnormal interaction between:
a) Metanephric blastema and ureteric bud
b) Pronephros and mesonephros
c) Ureter and cloaca
d) Glomerulus and collecting duct
Answer: a) Metanephric blastema and ureteric bud
Explanation: Improper reciprocal induction between the metanephric blastema and ureteric bud leads to polycystic or dysplastic kidneys. This defective signaling results in cystic dilation of renal tubules.
8. The mesonephric duct in males later forms:
a) Vas deferens and epididymis
b) Ureter
c) Prostate gland
d) Urethra
Answer: a) Vas deferens and epididymis
Explanation: The mesonephric (Wolffian) duct develops into male reproductive structures — epididymis, vas deferens, and seminal vesicles. In females, it regresses due to absence of testosterone.
9. Clinical: A child with a duplicated ureter likely had which developmental error?
a) Duplication of ureteric bud
b) Duplicated metanephric blastema
c) Fusion of mesonephric ducts
d) Early closure of cloaca
Answer: a) Duplication of ureteric bud
Explanation: Duplication of the ureteric bud before it contacts the metanephric blastema results in a duplicated ureter. The condition can be asymptomatic or lead to urinary obstruction.
10. The pronephros, mesonephros, and metanephros are derived from which embryonic tissue?
a) Intermediate mesoderm
b) Paraxial mesoderm
c) Lateral plate mesoderm
d) Endoderm
Answer: a) Intermediate mesoderm
Explanation: All three renal systems — pronephros, mesonephros, and metanephros — develop from the intermediate mesoderm. This tissue extends longitudinally along the dorsal body wall and differentiates into structures of the urinary and reproductive systems.
11. Clinical: An infant with Potter sequence most likely has which embryological defect?
a) Bilateral renal agenesis
b) Failure of ureteric bud branching
c) Persistence of pronephros
d) Early closure of cloacal membrane
Answer: a) Bilateral renal agenesis
Explanation: Potter sequence results from severe oligohydramnios due to bilateral renal agenesis. The absence of fetal urine causes pulmonary hypoplasia, limb deformities, and flattened facies — classic features of this syndrome.
Chapter: Embryology; Topic: Development of Digestive System; Subtopic: Development of Liver and Associated Structures
Key Definitions:
• Septum transversum: A thick mass of mesoderm between the heart and midgut that contributes to the diaphragm and gives rise to the fibrous stroma of the liver.
• Hepatic diverticulum: A ventral outgrowth from the foregut endoderm that gives rise to hepatocytes and bile ducts.
• Fibrous stroma: The connective tissue framework supporting liver parenchyma, derived from mesodermal cells.
• Foregut endoderm: The embryonic origin of epithelial liver cells, bile ducts, gallbladder, and pancreas.
Lead Question (NEET PG 2015):
1. Fibrous stroma of liver is derived from:
a) Foregut endoderm
b) Midgut endoderm
c) Hindgut endoderm
d) Septum transversum
Answer: d) Septum transversum
Explanation: The fibrous stroma and connective tissue framework of the liver originate from the mesoderm of the septum transversum. The liver parenchyma (hepatocytes) and biliary epithelium develop from endoderm of the foregut, while the stroma, Kupffer cells, and hemopoietic elements arise from mesodermal tissue. The septum transversum also contributes to the central tendon of the diaphragm, which later separates the thoracic and abdominal cavities. Thus, the liver has a dual origin — endodermal (epithelial) and mesodermal (supporting stroma).
Guessed Questions (Related to Development of Liver and Biliary System):
2. The hepatic cells of the liver are derived from:
a) Foregut endoderm
b) Septum transversum
c) Mesonephric duct
d) Hindgut endoderm
Answer: a) Foregut endoderm
Explanation: The hepatocytes and epithelial lining of bile ducts originate from the endoderm of the hepatic diverticulum, an outgrowth of the foregut. This diverticulum also forms the gallbladder and common bile duct.
3. Clinical: Incomplete closure of the connection between hepatic diverticulum and duodenum may lead to:
a) Biliary atresia
b) Choledochal cyst
c) Extrahepatic biliary fistula
d) Pancreatic duct anomaly
Answer: c) Extrahepatic biliary fistula
Explanation: Failure of proper separation between the hepatic diverticulum and duodenal endoderm during development can lead to abnormal communication, resulting in an extrahepatic biliary fistula.
4. The Kupffer cells of the liver are derived from:
a) Foregut endoderm
b) Septum transversum
c) Mesoderm of septum transversum
d) Yolk sac macrophages
Answer: d) Yolk sac macrophages
Explanation: Kupffer cells are liver macrophages derived from the monocyte lineage originating in the yolk sac mesoderm. They migrate to the liver during early hematopoiesis and remain as fixed macrophages in hepatic sinusoids.
5. Clinical: A newborn with jaundice and clay-colored stools is likely suffering from:
a) Biliary atresia
b) Pancreatitis
c) Duodenal stenosis
d) Hepatic cysts
Answer: a) Biliary atresia
Explanation: Biliary atresia results from failure of canalization of the extrahepatic bile ducts, leading to obstruction of bile flow, cholestasis, and jaundice. Clay-colored stools occur due to lack of bile pigments in the intestine.
6. The gallbladder develops from:
a) Foregut endoderm
b) Hindgut endoderm
c) Mesonephric duct
d) Septum transversum
Answer: a) Foregut endoderm
Explanation: The gallbladder and cystic duct arise from the cystic diverticulum, a part of the hepatic diverticulum from the ventral foregut endoderm. This endodermal origin gives rise to its epithelial lining.
7. Clinical: Accessory hepatic ducts result from:
a) Incomplete regression of biliary buds
b) Duplication of hepatic diverticulum
c) Defective bile canaliculi formation
d) Septum transversum anomalies
Answer: a) Incomplete regression of biliary buds
Explanation: Accessory hepatic ducts occur when additional biliary buds fail to regress during development, leading to extra bile ducts connecting to the gallbladder or common hepatic duct.
8. The liver bud grows into which embryonic structure?
a) Dorsal mesogastrium
b) Ventral mesogastrium
c) Septum transversum
d) Pleuroperitoneal membrane
Answer: c) Septum transversum
Explanation: The liver bud (hepatic diverticulum) grows into the septum transversum, where it differentiates into hepatic cords and bile ducts. The septum transversum provides the mesodermal stroma and the site for hepatic sinusoids.
9. Clinical: A congenital absence of gallbladder is due to failure of development of:
a) Cystic diverticulum
b) Hepatic diverticulum
c) Septum transversum
d) Common bile duct
Answer: a) Cystic diverticulum
Explanation: Agenesis of the gallbladder results from failure of cystic diverticulum formation or its degeneration during early embryonic life. It is usually asymptomatic and discovered incidentally.
10. The hepatic veins develop from:
a) Cardinal veins
b) Vitelline veins
c) Umbilical veins
d) Subcardinal veins
Answer: b) Vitelline veins
Explanation: The hepatic veins and sinusoids develop from the vitelline veins, which drain the yolk sac into the sinus venosus. These veins remodel to form the intrahepatic venous system of the liver.
11. Clinical: In a fetus with diaphragmatic hernia, part of the defect may involve improper development of which structure related to the liver?
a) Septum transversum
b) Pleuropericardial folds
c) Dorsal mesogastrium
d) Vitelline duct
Answer: a) Septum transversum
Explanation: The septum transversum forms the central tendon of the diaphragm. Failure in its complete formation or fusion with other diaphragmatic components can lead to congenital diaphragmatic hernia, sometimes affecting adjacent liver positioning.
Chapter: Embryology; Topic: Development of Pharyngeal Apparatus; Subtopic: Branchial Cleft Anomalies – Cysts, Sinuses, and Fistulae
Key Definitions:
• Branchial apparatus: A series of arches, pouches, and clefts that appear in the 4th week of embryonic life and contribute to the development of structures in the head and neck.
• Branchial cyst: A congenital epithelial cyst arising from incomplete obliteration of the second branchial cleft, typically located along the anterior border of the sternocleidomastoid muscle.
• Branchial sinus: A blind-ending tract that opens externally on the neck or internally into the pharynx.
• Branchial fistula: A complete tract connecting the skin to the pharynx, resulting from persistence of both branchial cleft and pouch.
Lead Question (NEET PG 2015, March 2013):
1. True about Branchial cyst is:
a) Cysts are more common than sinuses
b) Mostly arises from 2nd branchial system
c) Causes dysphagia and hoarseness
d) Sinus should always be operated
Answer: b) Mostly arises from 2nd branchial system
Explanation: A branchial cyst most commonly arises from remnants of the second branchial cleft or cervical sinus of His. It typically presents as a painless, fluctuant swelling in the upper lateral neck along the anterior border of the sternocleidomastoid. Cysts are less common than sinuses in general branchial anomalies, but among cysts, the second cleft origin predominates. These cysts may become infected or form fistulae. Dysphagia and hoarseness are rare since the lesion does not usually impinge upon deeper structures like the pharynx or larynx.
Guessed Questions (Related to Branchial Apparatus and Anomalies):
2. The second branchial cleft cyst is typically located:
a) Behind the auricle
b) Midline of neck
c) Along anterior border of sternocleidomastoid
d) Below the mandible
Answer: c) Along anterior border of sternocleidomastoid
Explanation: The second branchial cleft cyst lies along the anterior border of the upper third of the sternocleidomastoid muscle. It develops due to persistence of the cervical sinus formed between the 2nd and 4th branchial arches.
3. Clinical: A 12-year-old presents with a painless swelling in the lateral neck that moves neither with deglutition nor with tongue protrusion. The most likely diagnosis is:
a) Thyroglossal cyst
b) Branchial cyst
c) Dermoid cyst
d) Lymphangioma
Answer: b) Branchial cyst
Explanation: A branchial cyst presents as a painless, non-movable lateral neck mass that does not move with swallowing or tongue protrusion, distinguishing it from thyroglossal cysts, which are midline and move with tongue movements.
4. The first branchial cleft gives rise to which structure in normal development?
a) External auditory meatus
b) Middle ear cavity
c) Eustachian tube
d) Mastoid air cells
Answer: a) External auditory meatus
Explanation: The first branchial cleft forms the external auditory meatus, while the first branchial pouch forms the middle ear cavity and Eustachian tube. Persistence of the cleft can result in first branchial cleft anomalies near the ear or parotid gland.
5. Clinical: A patient with recurrent infections and a small opening along the anterior border of the sternocleidomastoid likely has:
a) Branchial sinus
b) Thyroglossal fistula
c) Dermoid sinus
d) Sebaceous cyst
Answer: a) Branchial sinus
Explanation: A branchial sinus is a blind tract opening on the lateral neck, commonly near the anterior border of the sternocleidomastoid, resulting from incomplete closure of the branchial cleft during development.
6. The internal opening of a complete branchial fistula opens into:
a) Tonsillar fossa
b) Pyriform fossa
c) Nasopharynx
d) Posterior pharyngeal wall
Answer: a) Tonsillar fossa
Explanation: A complete branchial fistula results from persistence of both the second branchial cleft and pouch. It extends from the skin externally to the tonsillar fossa internally, passing between the internal and external carotid arteries.
7. Clinical: Infection of a branchial cyst may present as:
a) Tender fluctuant neck swelling
b) Pain radiating to the ear
c) Fever and purulent discharge
d) All of the above
Answer: d) All of the above
Explanation: Secondary infection of a branchial cyst leads to tenderness, fluctuation, and abscess formation. Due to proximity to the glossopharyngeal nerve, pain may radiate to the ear. Surgical excision is the definitive treatment after infection subsides.
8. The branchial apparatus develops during which embryonic week?
a) 2nd week
b) 4th week
c) 6th week
d) 8th week
Answer: b) 4th week
Explanation: The branchial (pharyngeal) apparatus, comprising arches, clefts, and pouches, appears in the 4th week of development. It forms major structures of the head, neck, and face through endodermal, ectodermal, and mesodermal interactions.
9. The second branchial arch gives rise to all of the following except:
a) Stapes
b) Styloid process
c) Mandible
d) Lesser horn of hyoid
Answer: c) Mandible
Explanation: The mandible develops from the first branchial arch (Meckel’s cartilage), whereas the second arch (Reichert’s cartilage) gives rise to the stapes, styloid process, and lesser horn of hyoid.
10. Clinical: A patient presents with a cystic swelling just below the angle of the mandible that becomes inflamed intermittently. The most probable diagnosis is:
a) Branchial cyst
b) Parotid cyst
c) Thyroglossal cyst
d) Dermoid cyst
Answer: a) Branchial cyst
Explanation: A branchial cyst near the angle of the mandible is characteristic of a second branchial cleft remnant. Its typical lateral neck position and intermittent inflammation following upper respiratory infections make it pathognomonic.
11. Clinical: During surgery for a branchial fistula, injury to which nerve is most likely?
a) Hypoglossal nerve
b) Glossopharyngeal nerve
c) Facial nerve
d) Accessory nerve
Answer: b) Glossopharyngeal nerve
Explanation: The tract of a second branchial fistula passes between the internal and external carotid arteries and near the glossopharyngeal nerve. Hence, this nerve is at risk during surgical excision of the fistulous tract.
Chapter: Embryology; Topic: Early Embryonic Development; Subtopic: Notochord – Formation, Function, and Fate
Key Definitions:
• Notochord: A midline rod-like structure formed from mesodermal cells that serves as the primitive axis of the embryo and plays a key inductive role in neural development.
• Primary inductor: The notochord induces overlying ectoderm to form the neural plate, initiating neurulation.
• Hypoblast: The lower layer of the bilaminar embryonic disc, contributing to extraembryonic endoderm but not to the notochord.
• Nucleus pulposus: The central gelatinous core of the intervertebral disc, representing the remnant of the notochord in adults.
Lead Question (NEET PG 2015):
1. True about notochord are all except?
a) Defines axis of embryo
b) Serves as primary inductor
c) Derived from hypoblast
d) Remains as nucleus pulposus
Answer: c) Derived from hypoblast
Explanation: The notochord is derived from mesodermal cells migrating from the primitive node (Hensen’s node), not from the hypoblast. It defines the longitudinal axis of the embryo and induces the formation of the neural plate, marking it as the primary inductor in embryogenesis. Later in development, most of the notochord degenerates, but its remnants persist as the nucleus pulposus of intervertebral discs. The notochord also provides signals for differentiation of surrounding mesoderm into vertebral bodies and contributes to body plan organization.
Guessed Questions (Related to Notochord and Neural Induction):
2. The notochord develops from which embryonic structure?
a) Primitive node
b) Hypoblast
c) Amnion
d) Yolk sac
Answer: a) Primitive node
Explanation: The notochord arises from mesodermal cells migrating cranially from the primitive node. These cells form the notochordal process, which eventually develops into the solid notochordal rod that defines the embryonic midline.
3. Clinical: A congenital defect due to persistence of the notochord is known as:
a) Chordoma
b) Teratoma
c) Meningocele
d) Glioma
Answer: a) Chordoma
Explanation: Chordoma is a rare malignant tumor derived from remnants of the notochord, usually found at the base of the skull or sacrococcygeal region. It is slow-growing and locally invasive, arising from residual notochordal tissue that fails to regress completely.
4. The notochord induces the overlying ectoderm to form:
a) Neural plate
b) Neural crest
c) Somites
d) Myotome
Answer: a) Neural plate
Explanation: The notochord functions as a primary inductor by releasing signaling molecules that induce the overlying ectoderm to thicken and form the neural plate. This marks the beginning of neurulation and the development of the central nervous system.
5. Clinical: If notochordal induction fails, which of the following may result?
a) Neural tube defects
b) Craniofacial abnormalities
c) Hemivertebra
d) All of the above
Answer: d) All of the above
Explanation: Failure of notochordal induction disrupts neural tube formation, leading to neural tube defects such as spina bifida or anencephaly. It may also result in defective vertebral and craniofacial development due to its influence on mesodermal differentiation.
6. The notochord is located between:
a) Neural tube and endoderm
b) Ectoderm and mesoderm
c) Mesoderm and endoderm
d) Ectoderm and yolk sac
Answer: a) Neural tube and endoderm
Explanation: The notochord lies ventral to the neural tube and dorsal to the endoderm. This central position allows it to serve as an organizing center, influencing the development of both neural and mesodermal structures.
7. Clinical: A midline mass at the base of the skull extending into the nasopharynx could represent:
a) Chordoma
b) Meningocele
c) Craniopharyngioma
d) Lipoma
Answer: a) Chordoma
Explanation: Chordomas arise from persistent notochordal remnants and are often located in the clivus or sacrococcygeal region. They may present as midline masses with compressive symptoms in the cranial base or spine.
8. The notochord disappears during development except in which structure?
a) Vertebral body
b) Nucleus pulposus
c) Spinal cord
d) Neural crest
Answer: b) Nucleus pulposus
Explanation: Most of the notochord degenerates as vertebral bodies form, but remnants persist as the nucleus pulposus of intervertebral discs. This gelatinous core maintains flexibility and cushioning between vertebrae.
9. Which germ layer gives rise to the notochord?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) None of the above
Answer: b) Mesoderm
Explanation: The notochord is derived from mesodermal cells that migrate from the primitive node. This axial mesodermal structure is crucial for patterning the surrounding tissues during gastrulation and neurulation.
10. Clinical: A child presents with a dorsal midline sinus discharging mucoid material since birth. This may indicate persistence of:
a) Notochordal canal
b) Neural crest
c) Primitive streak
d) Neurenteric canal
Answer: d) Neurenteric canal
Explanation: Persistence of the neurenteric canal, which transiently connects the amniotic cavity with the yolk sac during notochord formation, may result in midline fistulae or cysts connecting spinal and gastrointestinal structures.
11. The notochordal process communicates transiently with the yolk sac via:
a) Neurenteric canal
b) Allantois
c) Cloacal membrane
d) Amniotic canal
Answer: a) Neurenteric canal
Explanation: During notochordal development, the notochordal process temporarily opens to the yolk sac through the neurenteric canal, maintaining continuity between the amniotic and yolk sac cavities until closure during normal development.
Chapter: Embryology; Topic: Ectodermal Derivatives; Subtopic: Neural Crest Cells – Migration and Derivatives
Key Definitions:
• Neural crest cells: A population of specialized cells derived from the ectoderm at the margins of the neural folds that migrate extensively and differentiate into diverse tissues throughout the body.
• Ectoderm: The outermost germ layer of the embryo, giving rise to the nervous system, epidermis, and various glands.
• Adrenal medulla: The inner region of the adrenal gland derived from neural crest cells, producing catecholamines like epinephrine and norepinephrine.
• Pia and arachnoid mater: Meningeal layers of neural crest origin surrounding the brain and spinal cord.
Lead Question (NEET PG 2015):
1. Structures derived from the neural crest are?
a) Pia
b) Dental papillae
c) Adrenal medulla
d) All of the above
Answer: d) All of the above
Explanation: Neural crest cells arise from the lateral edges of the neural folds during neurulation. They migrate throughout the body and give rise to multiple tissues, including melanocytes, dorsal root ganglia, sympathetic ganglia, Schwann cells, adrenal medulla, pia-arachnoid mater, and connective tissues of the head and neck. The dental papilla, which contributes to dentin formation, also originates from neural crest mesenchyme. Thus, all listed structures — pia, dental papilla, and adrenal medulla — are derived from neural crest cells, illustrating their remarkable multipotency and migratory capacity.
Guessed Questions (Related to Neural Crest Derivatives):
2. Which of the following is not derived from neural crest cells?
a) Melanocytes
b) Schwann cells
c) Anterior pituitary
d) Adrenal medulla
Answer: c) Anterior pituitary
Explanation: The anterior pituitary (adenohypophysis) is derived from ectoderm of Rathke’s pouch, not neural crest cells. The posterior pituitary arises from neuroectoderm. Neural crest cells, however, form melanocytes, Schwann cells, and adrenal medulla.
3. Clinical: A child presents with a tumor of the adrenal medulla. This tumor is derived from neural crest cells and is called:
a) Neuroblastoma
b) Wilms tumor
c) Nephroblastoma
d) Ependymoma
Answer: a) Neuroblastoma
Explanation: Neuroblastoma arises from neural crest-derived cells of the adrenal medulla or sympathetic ganglia. It secretes catecholamines and presents with hypertension, abdominal mass, and elevated urinary VMA levels.
4. The melanocytes of the skin are derived from which embryonic origin?
a) Surface ectoderm
b) Neural crest
c) Mesoderm
d) Endoderm
Answer: b) Neural crest
Explanation: Melanocytes arise from neural crest cells that migrate to the basal layer of the epidermis and produce melanin pigment. Defective migration results in hypopigmented conditions such as piebaldism or Waardenburg syndrome.
5. Clinical: Hirschsprung’s disease results from failure of migration of neural crest cells to form which structure?
a) Enteric ganglia
b) Dorsal root ganglia
c) Adrenal cortex
d) Motor neurons
Answer: a) Enteric ganglia
Explanation: Hirschsprung’s disease (congenital aganglionic megacolon) results from failure of neural crest cells to populate the wall of the distal colon, leading to absence of Auerbach’s and Meissner’s plexuses and functional obstruction.
6. Neural crest cells contribute to all of the following except:
a) Parafollicular cells of thyroid
b) Chromaffin cells of adrenal medulla
c) Odontoblasts
d) Hepatocytes
Answer: d) Hepatocytes
Explanation: Hepatocytes are derived from endoderm of the foregut. Neural crest cells give rise to parafollicular cells, chromaffin cells, odontoblasts, and various craniofacial connective tissues.
7. Clinical: A child with congenital absence of ganglion cells in the gut wall is likely to have defective migration of neural crest cells from:
a) Rhombencephalon
b) Telencephalon
c) Diencephalon
d) Mesencephalon
Answer: a) Rhombencephalon
Explanation: Neural crest cells originating from the rhombencephalon migrate caudally to form enteric ganglia. Defective migration results in Hirschsprung’s disease, leading to megacolon and constipation.
8. The meninges derived from neural crest cells are:
a) Dura mater
b) Pia and arachnoid mater
c) Only pia mater
d) All three layers
Answer: b) Pia and arachnoid mater
Explanation: The pia and arachnoid mater (leptomeninges) are derived from neural crest cells, while the dura mater arises from mesoderm. These layers protect the brain and spinal cord and contain cerebrospinal fluid within the subarachnoid space.
9. Neural crest cells contribute to formation of which cardiac structure?
a) Endocardial cushions
b) Aorticopulmonary septum
c) Myocardium
d) Pericardium
Answer: b) Aorticopulmonary septum
Explanation: Neural crest cells migrate into the truncus arteriosus and bulbus cordis to form the aorticopulmonary septum. Abnormal development leads to congenital heart defects such as Tetralogy of Fallot and transposition of great arteries.
10. Clinical: Waardenburg syndrome, characterized by heterochromia iridis, white forelock, and deafness, is caused by abnormal migration of:
a) Mesodermal cells
b) Neural crest cells
c) Endodermal cells
d) Neuroectodermal cells
Answer: b) Neural crest cells
Explanation: Waardenburg syndrome results from defective neural crest cell migration affecting melanocytes, craniofacial mesenchyme, and cochlear ganglion development. The disorder causes pigmentation anomalies and sensorineural deafness.
11. Neural crest derivatives include all except:
a) Schwann cells
b) Odontoblasts
c) Pia mater
d) Anterior horn motor neurons
Answer: d) Anterior horn motor neurons
Explanation: Motor neurons of the anterior horn are derived from neuroectoderm of the neural tube, not neural crest. Neural crest derivatives include Schwann cells, pia mater, odontoblasts, and sympathetic ganglia.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Formation of Heart Tube and Early Heart Development
Key Definitions:
• Cardiogenic area: The region of splanchnopleuric mesoderm located cranial to the neural plate where the heart begins to develop.
• Heart tube: A primitive linear structure formed by fusion of paired endocardial tubes during the 3rd week of development.
• Endocardial tube: Paired endothelial channels formed from the splanchnic mesoderm that fuse to form the primitive heart.
• Looping of heart: The process by which the straight heart tube bends and twists to form the future chambers of the heart.
Lead Question (NEET PG 2015):
1. Heart tube is formed at:
a) 3 weeks
b) 6 weeks
c) 10 weeks
d) 12 weeks
Answer: a) 3 weeks
Explanation: The heart tube begins to form at approximately 18–19 days (early in the 3rd week of embryonic life) from paired endocardial tubes in the cardiogenic mesoderm. These tubes fuse to form a single primitive heart tube as the embryo folds. The heart starts beating around day 22–23 and becomes the first functional organ of the embryo. Later, the tube undergoes looping, septation, and chamber formation. By the 8th week, the basic four-chambered structure of the heart is established. Thus, the heart tube appears in the 3rd week of development.
Guessed Questions (Related to Heart Tube Development and Embryonic Circulation):
2. The first organ to start functioning in the embryo is:
a) Brain
b) Heart
c) Liver
d) Kidney
Answer: b) Heart
Explanation: The heart is the first organ to become functional, beginning to beat around day 22–23. This ensures circulation of oxygen and nutrients throughout the developing embryo via the vitelline and umbilical vessels.
3. Clinical: Failure of fusion of the two endocardial heart tubes results in:
a) Cardia bifida
b) Dextrocardia
c) Atrial septal defect
d) Patent foramen ovale
Answer: a) Cardia bifida
Explanation: Cardia bifida is a rare condition in which the paired endocardial tubes fail to fuse, resulting in two separate beating hearts. This occurs due to failure of lateral folding during the 3rd week.
4. The cardiogenic area develops from which germ layer?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Neural crest
Answer: b) Mesoderm
Explanation: The cardiogenic region originates from splanchnopleuric mesoderm, which differentiates into endocardium, myocardium, and epicardium. This mesoderm gives rise to the entire heart and great vessels.
5. Clinical: A newborn with heart on the right side (dextrocardia) most likely has a defect in:
a) Cardiac looping
b) Cardiac septation
c) Chamber formation
d) Endocardial cushion development
Answer: a) Cardiac looping
Explanation: Dextrocardia results from abnormal looping of the heart tube to the left instead of the right. This may occur in isolation or as part of situs inversus, a mirror-image arrangement of organs.
6. The primitive heart tube is derived from which specific region of mesoderm?
a) Paraxial mesoderm
b) Intermediate mesoderm
c) Splanchnopleuric mesoderm
d) Somatopleuric mesoderm
Answer: c) Splanchnopleuric mesoderm
Explanation: The splanchnopleuric mesoderm of the cardiogenic area gives rise to the endothelial tubes that fuse to form the primitive heart. This layer also forms the myocardium and epicardium.
7. Clinical: A fetus with abnormal partitioning of truncus arteriosus will likely develop:
a) Tetralogy of Fallot
b) Patent ductus arteriosus
c) Coarctation of aorta
d) Transposition of great vessels
Answer: a) Tetralogy of Fallot
Explanation: Improper division of the truncus arteriosus by the spiral aorticopulmonary septum leads to Tetralogy of Fallot, which includes ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy.
8. The heart tube begins to beat at approximately:
a) Day 14
b) Day 18
c) Day 22
d) Day 28
Answer: c) Day 22
Explanation: The primitive heart tube begins rhythmic contractions around day 22, establishing the first embryonic circulation. This ensures efficient transport of nutrients and waste products even before placental circulation is fully established.
9. Clinical: A neonate with cyanosis and parallel great vessels likely has a defect in which developmental process?
a) Abnormal aorticopulmonary septum formation
b) Defective endocardial cushion fusion
c) Failure of atrial septation
d) Abnormal truncal ridge migration
Answer: a) Abnormal aorticopulmonary septum formation
Explanation: Transposition of the great vessels occurs due to failure of the aorticopulmonary septum to spiral during development, causing the aorta to arise from the right ventricle and the pulmonary trunk from the left ventricle.
10. The sinus venosus contributes to formation of which cardiac structure?
a) Right atrium (smooth part)
b) Left ventricle
c) Pulmonary trunk
d) Aortic arch
Answer: a) Right atrium (smooth part)
Explanation: The right horn of the sinus venosus becomes incorporated into the wall of the right atrium, forming its smooth posterior portion known as the sinus venarum. This region receives blood from the superior and inferior vena cava.
11. Clinical: An infant with a persistent truncus arteriosus has failure in the development of which embryological structure?
a) Aorticopulmonary septum
b) Bulbus cordis
c) Sinus venosus
d) Endocardial cushions
Answer: a) Aorticopulmonary septum
Explanation: Persistent truncus arteriosus results from failure of the truncal ridges and bulbar ridges to fuse and form the aorticopulmonary septum. This leads to a single arterial trunk supplying both the systemic and pulmonary circulations.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Formation of Heart Tube and Cardiac Jelly Composition
Key Definitions:
• Heart tube: The primitive cardiac structure formed by fusion of paired endothelial tubes within the cardiogenic mesoderm, which later differentiates into chambers of the heart.
• Cardiac jelly: The gelatinous connective tissue between the endocardium and myocardium that plays a vital role in cardiac morphogenesis.
• Hyaluronic acid: A glycosaminoglycan secreted mainly by myocardium that provides structural support during heart tube formation.
• Myocardium: The muscular layer of the heart derived from splanchnic mesoderm responsible for contraction and cardiac jelly secretion.
Lead Question (NEET PG 2015):
1. Heart tube is formed in:
a) Hyaluronic acid secreted by endocardium
b) Chondroitin sulfate secreted by endocardium
c) Hyaluronic acid secreted by myocardium
d) Chondroitin sulfate secreted by myocardium
Answer: c) Hyaluronic acid secreted by myocardium
Explanation: The heart tube forms within a gelatinous matrix called cardiac jelly, which lies between the endocardium and myocardium. This jelly primarily contains hyaluronic acid secreted by the myocardium. It plays a crucial role in maintaining the shape of the heart tube, aiding endocardial cushion formation, and guiding cardiac septation. The myocardium (derived from splanchnopleuric mesoderm) secretes this substance early in cardiac morphogenesis. As the heart develops, the cardiac jelly is gradually reduced and replaced by the developing extracellular matrix and myocardial trabeculae.
Guessed Questions (Related to Heart Tube and Cardiac Jelly Formation):
2. The cardiac jelly is located between which two layers of the developing heart?
a) Endocardium and myocardium
b) Myocardium and epicardium
c) Endocardium and pericardium
d) Myocardium and mesocardium
Answer: a) Endocardium and myocardium
Explanation: The cardiac jelly is a thick, acellular matrix located between the endocardial endothelial layer and the muscular myocardium. It supports the developing heart and later contributes to endocardial cushion formation, essential for septation.
3. Clinical: A defect in endocardial cushion development can result in:
a) Atrioventricular septal defect
b) Tetralogy of Fallot
c) Coarctation of aorta
d) Patent ductus arteriosus
Answer: a) Atrioventricular septal defect
Explanation: Endocardial cushions, derived partly from cardiac jelly, contribute to formation of the atrial and ventricular septa and atrioventricular valves. Their abnormal development leads to AV septal defects, commonly seen in Down syndrome.
4. The myocardium is derived from which embryonic layer?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Neural crest
Answer: b) Mesoderm
Explanation: The myocardium originates from the splanchnopleuric layer of lateral plate mesoderm. This mesodermal origin provides contractile cardiac muscle fibers and secretes hyaluronic acid for cardiac jelly formation.
5. Clinical: A baby presents with a single atrioventricular valve and a large central septal defect. The most likely embryologic cause is:
a) Defective endocardial cushion fusion
b) Failure of spiral septum formation
c) Abnormal cardiac looping
d) Improper neural crest migration
Answer: a) Defective endocardial cushion fusion
Explanation: Endocardial cushions contribute to both the atrial and ventricular septa and the formation of AV valves. Failure of their fusion results in complete AV canal defects and single common AV valves.
6. The earliest sign of heart development occurs at which embryonic age?
a) Day 10
b) Day 15
c) Day 18
d) Day 25
Answer: c) Day 18
Explanation: Around day 18, paired endothelial tubes form in the cardiogenic mesoderm. These tubes fuse during the 3rd week to create the primitive heart tube, which begins to beat by day 22–23.
7. Clinical: Excessive persistence of cardiac jelly could interfere with which developmental process?
a) Septation of the heart
b) Formation of cardiac valves
c) Chamber formation
d) All of the above
Answer: d) All of the above
Explanation: Cardiac jelly must be resorbed properly for septation and valve formation. Persistent jelly obstructs the formation of the endocardial cushions, leading to defects like AV septal defects or valve malformations.
8. The heart tube starts to beat at approximately which day of development?
a) Day 15
b) Day 18
c) Day 22
d) Day 28
Answer: c) Day 22
Explanation: Around day 22, the primitive heart tube begins rhythmic contractions, establishing circulation between the embryo and yolk sac. This is the earliest functional activity of any organ system.
9. Clinical: Incomplete resorption of cardiac jelly during development may lead to:
a) Valvular stenosis
b) Aortic arch anomalies
c) Coarctation of the aorta
d) Patent foramen ovale
Answer: a) Valvular stenosis
Explanation: Excessive cardiac jelly can hinder proper valve formation, resulting in thickened or stenotic valves. Normal valve development requires controlled resorption of jelly and remodeling of endocardial cushions.
10. The cardiac jelly primarily consists of:
a) Collagen and elastic fibers
b) Hyaluronic acid and glycoproteins
c) Chondroitin sulfate and fibrin
d) Fibronectin and laminin only
Answer: b) Hyaluronic acid and glycoproteins
Explanation: Cardiac jelly is rich in hyaluronic acid, glycoproteins, and proteoglycans. These substances provide a hydrophilic matrix that maintains the shape of the primitive heart and supports endocardial cushion development.
11. Clinical: If the myocardium fails to secrete sufficient hyaluronic acid, what developmental consequence may occur?
a) Defective endocardial cushion formation
b) Underdeveloped cardiac chambers
c) Impaired looping of the heart tube
d) All of the above
Answer: d) All of the above
Explanation: Hyaluronic acid secreted by the myocardium provides the matrix for heart tube expansion and endocardial cushion formation. Deficiency in its secretion can result in abnormal septation, looping, and underdeveloped cardiac morphology.
Chapter: Embryology; Topic: Fetal Circulation; Subtopic: Fate of Umbilical Vessels After Birth
Key Definitions:
• Umbilical arteries: Paired vessels carrying deoxygenated blood from the fetus to the placenta during intrauterine life.
• Umbilical vein: A single vessel that carries oxygenated blood from the placenta to the fetus.
• Ligamentum arteriosum: The fibrous remnant of the ductus arteriosus connecting the pulmonary artery to the aortic arch.
• Medial umbilical ligament: The postnatal fibrous remnant of the distal portion of the umbilical arteries that runs along the inner abdominal wall.
Lead Question (NEET PG 2015):
1. Remnant of umbilical artery:
a) Ligamentum arteriosum
b) Ligament teres
c) Ligamentum venosum
d) Medial umbilical ligament
Answer: d) Medial umbilical ligament
Explanation: The umbilical arteries carry deoxygenated blood from the fetus to the placenta. After birth, the distal parts of these arteries close and form the medial umbilical ligaments, while the proximal parts remain patent as the superior vesical arteries supplying the urinary bladder. These fibrous ligaments are seen on the posterior aspect of the anterior abdominal wall, covered by peritoneum. In contrast, the ligamentum teres is derived from the umbilical vein, and the ligamentum arteriosum arises from the ductus arteriosus.
Guessed Questions (Related to Fetal Circulation and Umbilical Remnants):
2. The remnant of the umbilical vein in adults is known as:
a) Ligamentum arteriosum
b) Ligamentum venosum
c) Ligamentum teres hepatis
d) Medial umbilical ligament
Answer: c) Ligamentum teres hepatis
Explanation: The umbilical vein becomes the ligamentum teres hepatis after birth. It lies in the free margin of the falciform ligament of the liver and connects to the left branch of the portal vein.
3. Clinical: In a newborn, failure of closure of the umbilical vein results in:
a) Patent ductus venosus
b) Umbilical hernia
c) Persistent umbilical vein
d) Patent ductus arteriosus
Answer: c) Persistent umbilical vein
Explanation: A persistent umbilical vein can remain open and act as a collateral pathway in portal hypertension. This condition may manifest as caput medusae due to engorged paraumbilical veins.
4. The ductus arteriosus connects which two fetal structures?
a) Right atrium and left atrium
b) Right ventricle and aorta
c) Pulmonary artery and aorta
d) Left atrium and aorta
Answer: c) Pulmonary artery and aorta
Explanation: The ductus arteriosus connects the pulmonary artery to the descending aorta in fetal life, allowing blood to bypass the nonfunctioning lungs. Postnatally, it closes to form the ligamentum arteriosum.
5. Clinical: Failure of ductus arteriosus to close after birth leads to:
a) Coarctation of aorta
b) Patent ductus arteriosus
c) Tetralogy of Fallot
d) Atrial septal defect
Answer: b) Patent ductus arteriosus
Explanation: Patent ductus arteriosus (PDA) occurs when the ductus arteriosus remains open, leading to a left-to-right shunt of blood from the aorta to the pulmonary artery, causing pulmonary hypertension and heart failure if untreated.
6. The proximal part of the umbilical arteries after birth remains patent as:
a) Superior vesical arteries
b) Inferior epigastric arteries
c) Umbilical vein
d) Obturator arteries
Answer: a) Superior vesical arteries
Explanation: The proximal portions of the umbilical arteries persist as the superior vesical arteries, supplying the superior part of the urinary bladder and occasionally the ductus deferens in males.
7. Clinical: The ligamentum arteriosum is located between which structures in adults?
a) Pulmonary artery and aortic arch
b) Pulmonary vein and left atrium
c) Aorta and superior vena cava
d) Right ventricle and pulmonary trunk
Answer: a) Pulmonary artery and aortic arch
Explanation: The ligamentum arteriosum is the fibrous remnant of the ductus arteriosus, connecting the left pulmonary artery to the aortic arch. It is located near the left recurrent laryngeal nerve, which loops around it.
8. Clinical: A newborn with cyanosis that improves with indomethacin likely has:
a) Patent ductus arteriosus
b) Transposition of great vessels
c) Coarctation of aorta
d) Persistent foramen ovale
Answer: a) Patent ductus arteriosus
Explanation: Indomethacin inhibits prostaglandin synthesis, promoting closure of the ductus arteriosus in neonates with PDA. In contrast, prostaglandins maintain ductal patency in conditions like transposition of great vessels.
9. The ligamentum venosum in adults represents the remnant of:
a) Umbilical vein
b) Ductus venosus
c) Umbilical artery
d) Ductus arteriosus
Answer: b) Ductus venosus
Explanation: The ductus venosus, which shunts oxygenated blood from the umbilical vein to the inferior vena cava bypassing the liver, becomes the ligamentum venosum after birth and lies between the left lobe and caudate lobe of the liver.
10. Clinical: A patient with portal hypertension shows distended veins radiating from the umbilicus. These represent:
a) Recanalized umbilical vein
b) Umbilical artery dilation
c) Patent ductus venosus
d) Inferior epigastric varices
Answer: a) Recanalized umbilical vein
Explanation: In portal hypertension, the ligamentum teres (remnant of the umbilical vein) may reopen, forming collateral circulation between the portal and systemic veins, resulting in caput medusae appearance.
11. Clinical: A stab wound near the medial umbilical ligament may injure which underlying structure?
a) Inferior epigastric artery
b) Urinary bladder
c) Superior vesical artery
d) Deep circumflex iliac vein
Answer: c) Superior vesical artery
Explanation: The superior vesical artery lies close to the medial umbilical ligament, which is the remnant of the umbilical artery. Penetrating injuries in this region can damage the bladder or its arterial supply.