Chapter: Embryology; Topic: Development of Genitourinary System; Subtopic: Derivatives of Paramesonephric and Mesonephric Ducts
Keyword Definitions:
• Paramesonephric duct (Müllerian duct): Embryonic structure that develops into female genital ducts.
• Mesonephric duct (Wolffian duct): Gives rise to male genital ducts like epididymis and vas deferens.
• Prostatic utricle: A small pouch in males representing the remnant of the Müllerian duct.
• Gartner’s duct: A remnant of the Wolffian duct in females.
• Paraphoron: A vestigial structure in the male genital ridge.
• Trigone of bladder: Formed from the mesonephric ducts, not paramesonephric.
Lead Question - 2015
Which of the following is a derivative of paramesonephric duct in males?
a) Trigone of bladder
b) Paraphoron
c) Prostatic utricle
d) Gartner's duct
Explanation (Answer: c) Prostatic utricle
The paramesonephric ducts regress in males under anti-Müllerian hormone influence, but remnants persist as the prostatic utricle and appendix testis. The prostatic utricle is a small, blind sac in the prostate near the verumontanum, representing the Müllerian duct homologue. Other options derive from mesonephric duct remnants.
1. Which structure in the male represents the remnant of the paramesonephric duct?
a) Epididymis
b) Appendix testis
c) Seminal vesicle
d) Ejaculatory duct
Explanation (Answer: b) Appendix testis
The appendix testis is a small, pedunculated structure on the upper pole of the testis derived from the paramesonephric duct. It is a vestigial remnant similar to the prostatic utricle. The epididymis and ejaculatory ducts originate from the mesonephric duct system, not from the paramesonephric duct.
2. In the male fetus, regression of paramesonephric ducts occurs due to secretion of which hormone?
a) Testosterone
b) Progesterone
c) Anti-Müllerian hormone
d) Estrogen
Explanation (Answer: c) Anti-Müllerian hormone
Sertoli cells of the fetal testes secrete Anti-Müllerian hormone (AMH), also known as Müllerian inhibiting substance. It causes regression of the paramesonephric ducts in male embryos. In its absence, Müllerian derivatives develop, leading to persistence of female internal structures in males.
3. Persistence of the Müllerian duct in a male can result in which clinical condition?
a) Cryptorchidism
b) Persistent Müllerian duct syndrome
c) Hypospadias
d) Testicular feminization
Explanation (Answer: b) Persistent Müllerian duct syndrome)
Persistent Müllerian duct syndrome (PMDS) is caused by deficiency or insensitivity to AMH. Despite a normal male genotype (46,XY) and external genitalia, Müllerian duct structures like uterus and fallopian tubes persist internally. This is a rare cause of cryptorchidism or inguinal hernia in males.
4. Which of the following is a remnant of the mesonephric duct in females?
a) Uterine tube
b) Gartner’s duct
c) Uterus
d) Prostatic utricle
Explanation (Answer: b) Gartner’s duct
Gartner’s duct is a vestigial remnant of the mesonephric (Wolffian) duct in females. It may persist as small cysts along the vaginal wall or broad ligament. The uterine tubes and uterus are paramesonephric derivatives, while the prostatic utricle is a male Müllerian remnant.
5. A 22-year-old male presents with infertility and presence of uterus-like structure on imaging. Which embryological failure explains this finding?
a) Failure of Leydig cell differentiation
b) Failure of AMH secretion
c) Failure of Wolffian duct development
d) Failure of gubernaculum regression
Explanation (Answer: b) Failure of AMH secretion)
Infertility with a uterus-like structure in a genetic male indicates Persistent Müllerian duct syndrome due to failure of Anti-Müllerian hormone (AMH) secretion by Sertoli cells. This results in persistence of Müllerian derivatives like uterus and fallopian tubes despite normal male external genitalia.
6. In females, paramesonephric ducts fuse to form which structure?
a) Urethra
b) Ovaries
c) Uterus
d) Clitoris
Explanation (Answer: c) Uterus)
In females, the paramesonephric (Müllerian) ducts fuse caudally to form the uterus, cervix, and upper part of the vagina. The unfused cranial portions form the uterine tubes. This fusion is crucial for normal uterine development, and its failure leads to uterine anomalies such as septate or bicornuate uterus.
7. Which structure develops from the mesonephric duct in males?
a) Fallopian tube
b) Prostate
c) Vas deferens
d) Appendix testis
Explanation (Answer: c) Vas deferens)
In males, the mesonephric (Wolffian) duct gives rise to the epididymis, vas deferens, ejaculatory duct, and seminal vesicles under the influence of testosterone. The paramesonephric ducts regress except for small remnants such as the prostatic utricle and appendix testis.
8. A 3-year-old boy with undescended testes shows a small midline cyst near the prostate. This is most likely a remnant of which embryonic duct?
a) Mesonephric duct
b) Paramesonephric duct
c) Ureteric bud
d) Allantois
Explanation (Answer: b) Paramesonephric duct)
A small midline cyst near the prostate represents a prostatic utricle cyst, derived from the paramesonephric (Müllerian) duct. These cysts may persist in males due to incomplete regression of Müllerian remnants and may cause urinary or ejaculatory obstruction if large.
9. Which of the following correctly matches the embryonic origin and adult structure?
a) Mesonephric duct – Uterine tube
b) Paramesonephric duct – Epididymis
c) Paramesonephric duct – Uterus
d) Mesonephric duct – Ovary
Explanation (Answer: c) Paramesonephric duct – Uterus)
The paramesonephric duct develops into the uterus, uterine tubes, and upper vagina in females. In males, it largely regresses due to AMH. The mesonephric duct gives rise to male reproductive ducts like vas deferens and seminal vesicle, not to female structures.
10. A male neonate presents with bilateral inguinal hernias and Müllerian duct remnants. Which of the following best explains this condition?
a) Lack of testosterone production
b) Lack of dihydrotestosterone
c) Mutation in AMH gene
d) Mutation in androgen receptor
Explanation (Answer: c) Mutation in AMH gene)
A mutation in the Anti-Müllerian hormone (AMH) gene or its receptor causes Persistent Müllerian duct syndrome. It presents in males with normal external genitalia but persistence of uterus and fallopian tubes, often associated with inguinal hernias or undescended testes due to the Müllerian structures impeding descent.
Chapter: Neuroanatomy; Topic: Nervous Tissue; Subtopic: Myelination in the Peripheral and Central Nervous System
Keyword Definitions:
• Myelin sheath: A fatty insulating layer that increases the speed of nerve impulse conduction.
• Schwann cells: Glial cells responsible for myelination in the peripheral nervous system.
• Oligodendrocytes: Cells that myelinate axons in the central nervous system.
• Astrocytes: Star-shaped glial cells that maintain the blood-brain barrier and nutrient supply.
• Ependymal cells: Line ventricles of the brain and central canal of the spinal cord; produce cerebrospinal fluid.
• Nodes of Ranvier: Gaps between myelin segments allowing saltatory conduction.
Lead Question - 2015
Myelination in peripheral nervous system is done by:
a) Astrocytes
b) Oligodendrocytes
c) Ependymal cells
d) Schwann cells
Explanation (Answer: d) Schwann cells
In the peripheral nervous system, Schwann cells produce the myelin sheath around axons. Each Schwann cell myelinates one segment of a single axon. In contrast, oligodendrocytes myelinate several axons in the CNS. Schwann cells also assist in nerve regeneration, unlike CNS glial cells that inhibit axonal regrowth.
1. Myelination in the central nervous system is performed by which type of cell?
a) Schwann cells
b) Astrocytes
c) Oligodendrocytes
d) Microglia
Explanation (Answer: c) Oligodendrocytes
Oligodendrocytes are responsible for myelination of axons in the central nervous system (CNS). One oligodendrocyte can myelinate several axons simultaneously. Damage to these cells, as seen in multiple sclerosis, leads to demyelination and impaired nerve conduction. They differ from Schwann cells that myelinate peripheral nerves.
2. A 30-year-old woman presents with blurred vision and limb weakness. MRI shows demyelination in the CNS. The affected cells are:
a) Schwann cells
b) Oligodendrocytes
c) Astrocytes
d) Microglia
Explanation (Answer: b) Oligodendrocytes)
In multiple sclerosis, there is autoimmune destruction of oligodendrocytes, leading to CNS demyelination. This causes conduction block and neurological symptoms like visual loss and muscle weakness. Peripheral nerves remain unaffected because their myelin is formed by Schwann cells, not oligodendrocytes.
3. Which of the following statements regarding Schwann cells is true?
a) Each Schwann cell myelinates multiple axons
b) Schwann cells are found only in the CNS
c) They aid in axonal regeneration after injury
d) They produce cerebrospinal fluid
Explanation (Answer: c) They aid in axonal regeneration after injury)
Schwann cells not only form the myelin sheath in peripheral nerves but also assist in axonal regeneration following injury by creating a guiding tube. They release neurotrophic factors promoting regrowth. In contrast, CNS regeneration is limited due to inhibitory molecules from oligodendrocytes and glial scarring by astrocytes.
4. Which cell forms myelin around multiple axons in the central nervous system?
a) Microglia
b) Oligodendrocytes
c) Schwann cells
d) Astrocytes
Explanation (Answer: b) Oligodendrocytes)
Oligodendrocytes extend cytoplasmic processes to wrap myelin around several axons within the CNS. Each cell may myelinate up to 30 axons. This arrangement contrasts with Schwann cells, which myelinate only one segment of one axon in the PNS. Oligodendrocyte injury leads to CNS demyelination.
5. A patient with Guillain-Barré syndrome shows segmental demyelination. Which cell type is primarily affected?
a) Oligodendrocytes
b) Microglia
c) Schwann cells
d) Astrocytes
Explanation (Answer: c) Schwann cells)
Guillain-Barré syndrome (GBS) is an acute demyelinating disorder of the peripheral nervous system caused by immune-mediated destruction of Schwann cells. It leads to ascending muscle weakness and areflexia. CNS remains unaffected because oligodendrocytes are not involved. Early management with plasmapheresis aids recovery.
6. Which of the following glial cells forms the blood-brain barrier by connecting neurons to capillaries?
a) Oligodendrocytes
b) Astrocytes
c) Schwann cells
d) Microglia
Explanation (Answer: b) Astrocytes)
Astrocytes are star-shaped glial cells that provide metabolic support to neurons and form part of the blood-brain barrier via their end-feet processes. They regulate ionic balance and neurotransmitter clearance. Though not involved in myelination, they are crucial in maintaining CNS homeostasis and repair after injury.
7. Myelin sheath primarily facilitates which of the following functions?
a) Neurotransmitter synthesis
b) Rapid saltatory conduction
c) Receptor activation
d) Axonal branching
Explanation (Answer: b) Rapid saltatory conduction)
The myelin sheath insulates axons and allows action potentials to jump between the Nodes of Ranvier, a process called saltatory conduction. This greatly increases the velocity of nerve impulses. Loss of myelin, as seen in demyelinating diseases, causes conduction slowing or block.
8. A child with congenital absence of Schwann cells will most likely present with:
a) Hyperreflexia
b) Slowed peripheral nerve conduction
c) Enhanced synaptic transmission
d) Increased CNS myelination
Explanation (Answer: b) Slowed peripheral nerve conduction)
Absence of Schwann cells results in loss of peripheral myelin and markedly reduced nerve conduction velocity. Schwann cells are essential for saltatory conduction and nerve regeneration. Such a condition leads to weakness, sensory loss, and reduced reflexes typical of peripheral neuropathy.
9. Which of the following correctly pairs the glial cell with its function?
a) Ependymal cell – Blood-brain barrier
b) Oligodendrocyte – PNS myelination
c) Schwann cell – PNS myelination
d) Astrocyte – Cerebrospinal fluid secretion
Explanation (Answer: c) Schwann cell – PNS myelination)
Schwann cells myelinate peripheral nerve fibers and help in axonal regeneration. In contrast, oligodendrocytes myelinate CNS fibers, ependymal cells secrete cerebrospinal fluid, and astrocytes form the blood-brain barrier. Thus, Schwann cells are critical for peripheral nerve repair and conduction efficiency.
10. A 40-year-old male develops progressive limb weakness following Campylobacter infection. The pathology involves:
a) Destruction of oligodendrocytes
b) Degeneration of Schwann cells
c) Axonal sprouting in CNS
d) Astrocyte proliferation
Explanation (Answer: b) Degeneration of Schwann cells)
In post-infectious Guillain-Barré syndrome, immune-mediated damage to Schwann cells causes segmental demyelination of peripheral nerves. The loss of myelin slows conduction and produces ascending paralysis. Recovery occurs as Schwann cells remyelinate axons, highlighting their vital role in nerve repair.
Chapter: Embryology; Topic: Development of Head and Neck; Subtopic: Pharyngeal Arches and Their Derivatives
Keyword Definitions:
• Pharyngeal arches: Embryonic swellings on the lateral sides of the head and neck that give rise to various head and neck structures.
• Meckel’s cartilage: Cartilage of the first pharyngeal arch that forms malleus and incus.
• Reichert’s cartilage: Cartilage of the second pharyngeal arch forming stapes and styloid process.
• Malleus and Incus: Two middle ear ossicles derived from the first arch.
• Stapes: Middle ear ossicle derived from the second arch.
• Mandibular arch: Another name for the first pharyngeal arch.
Lead Question - 2015
Malleus and incus are derived from?
a) 1st Arch
b) 2nd Arch
c) 3rd Arch
d) 4th Arch
Explanation (Answer: a) 1st Arch
The malleus and incus are derived from Meckel’s cartilage of the first pharyngeal (mandibular) arch. This arch also contributes to the maxilla, mandible, and muscles of mastication. The stapes and styloid process originate from Reichert’s cartilage of the second arch, while the third and fourth arches form parts of the hyoid and laryngeal cartilages.
1. Which pharyngeal arch gives rise to the stapes and styloid process?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation (Answer: b) Second arch)
The second pharyngeal arch, also called the hyoid arch, gives rise to the stapes, styloid process, lesser horn and upper part of the hyoid bone. Its cartilage is called Reichert’s cartilage. Muscles derived from this arch include muscles of facial expression supplied by the facial nerve (cranial nerve VII).
2. The mandible develops from which pharyngeal arch?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation (Answer: a) First arch)
The mandible arises from the first pharyngeal arch through ossification of Meckel’s cartilage. This arch is innervated by the mandibular division of the trigeminal nerve (V3). Other derivatives include the maxilla, malleus, incus, and muscles of mastication, making it the most significant arch in facial development.
3. A congenital anomaly involving the stapes and styloid process suggests a defect in which embryonic structure?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation (Answer: b) Second pharyngeal arch)
The second pharyngeal arch (Reichert’s cartilage) forms the stapes, styloid process, and part of the hyoid bone. A defect in this arch can cause abnormalities in hearing and neck bone formation. It is innervated by the facial nerve, which also supplies its derived muscles of facial expression.
4. Which of the following muscles is derived from the first pharyngeal arch?
a) Stylopharyngeus
b) Buccinator
c) Tensor tympani
d) Cricothyroid
Explanation (Answer: c) Tensor tympani)
The tensor tympani muscle arises from the first pharyngeal arch. It functions to dampen loud sounds by tensing the tympanic membrane. Other muscles of this arch include muscles of mastication, mylohyoid, and tensor veli palatini, all supplied by the mandibular nerve (V3), a branch of the trigeminal nerve.
5. A newborn with congenital absence of the stapes likely has a developmental defect involving:
a) Reichert’s cartilage
b) Meckel’s cartilage
c) Fourth arch cartilage
d) Thyroid cartilage
Explanation (Answer: a) Reichert’s cartilage)
Reichert’s cartilage is the cartilage of the second pharyngeal arch. It gives rise to the stapes, styloid process, stylohyoid ligament, and lesser horn of the hyoid bone. Any defect or interruption in its development results in congenital stapes absence or middle ear deformities leading to conductive hearing loss.
6. The third pharyngeal arch gives rise to which of the following structures?
a) Greater horn of hyoid bone
b) Styloid process
c) Thyroid cartilage
d) Mandible
Explanation (Answer: a) Greater horn of hyoid bone)
The third pharyngeal arch forms the greater horn and lower part of the hyoid bone and gives rise to the stylopharyngeus muscle, supplied by the glossopharyngeal nerve (cranial nerve IX). It plays a key role in forming parts of the pharyngeal wall and supports the tongue and laryngeal framework.
7. A patient presents with abnormal facial expressions and maldevelopment of the styloid process. The affected cranial nerve is:
a) Trigeminal nerve
b) Facial nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation (Answer: b) Facial nerve)
The facial nerve (cranial nerve VII) innervates structures derived from the second pharyngeal arch. These include muscles of facial expression and derivatives of Reichert’s cartilage like the styloid process. Hence, damage or developmental anomalies affecting this arch result in facial muscle weakness or asymmetry.
8. Which of the following cartilages is derived from the fourth pharyngeal arch?
a) Cricoid cartilage
b) Thyroid cartilage
c) Arytenoid cartilage
d) Epiglottic cartilage
Explanation (Answer: b) Thyroid cartilage)
The fourth and sixth pharyngeal arches together form most of the laryngeal cartilages. The thyroid cartilage arises mainly from the fourth arch, while the cricoid, arytenoid, and corniculate cartilages develop from the sixth. The fourth arch is supplied by the superior laryngeal branch of the vagus nerve.
9. The muscles of mastication develop from which pharyngeal arch?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation (Answer: a) First arch)
Muscles of mastication—masseter, temporalis, and pterygoids—arise from the first pharyngeal (mandibular) arch. They are supplied by the mandibular branch of the trigeminal nerve (V3). This arch also contributes to Meckel’s cartilage, from which the malleus and incus develop, forming essential components of the middle ear.
10. A 3-year-old child presents with conductive hearing loss. Imaging reveals malformed malleus and incus. Which embryonic origin is implicated?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation (Answer: a) First pharyngeal arch)
Malformed malleus and incus indicate developmental defects of the first pharyngeal (mandibular) arch. Meckel’s cartilage of this arch forms these ossicles. The associated cranial nerve is the mandibular division of the trigeminal nerve, and defects often result in both auditory and jaw malformations in affected children.
Chapter: Embryology; Topic: Development of Heart; Subtopic: Interatrial Septum and Fossa Ovalis
Keyword Definitions:
• Fossa ovalis: A depression in the interatrial septum of the right atrium, representing the closed foramen ovale of the fetal heart.
• Limbus fossa ovalis (Annulus ovalis): Raised margin surrounding the fossa ovalis, derived from the septum secundum.
• Septum primum: The first septum growing downward to separate the primitive atrium.
• Septum secundum: A crescent-shaped fold that overlaps the foramen ovale and forms the limbus.
• Foramen ovale: A fetal opening between the atria allowing blood to bypass the lungs.
• Interatrial septum: Wall separating right and left atria, formed from both septum primum and secundum.
Lead Question - 2015
False about limbus fossa ovalis -
a) Situated above fossa ovalis
b) In right atrium
c) Derived from septum primum
d) Also called Annulus ovalis
Explanation (Answer: c) Derived from septum primum)
The limbus fossa ovalis, also called the annulus ovalis, is a raised ridge located around the upper margin of the fossa ovalis in the right atrium. It is derived from the septum secundum, not from the septum primum. The septum primum forms the floor of the fossa ovalis itself.
1. The fossa ovalis in the adult heart is a remnant of which embryonic structure?
a) Foramen primum
b) Septum secundum
c) Foramen ovale
d) Ductus arteriosus
Explanation (Answer: c) Foramen ovale)
The fossa ovalis in the adult right atrium represents the closed foramen ovale of the fetal heart. During fetal life, the foramen ovale allowed blood to pass from the right atrium to the left atrium, bypassing pulmonary circulation. After birth, it closes functionally and later anatomically to form the fossa ovalis.
2. The upper border of the fossa ovalis is known as:
a) Septum primum
b) Septum intermedium
c) Limbus fossa ovalis
d) Crista terminalis
Explanation (Answer: c) Limbus fossa ovalis)
The limbus fossa ovalis forms the prominent upper margin of the fossa ovalis in the right atrium. It is derived from the septum secundum. It appears as a raised border surrounding the fossa, demarcating the area of embryonic fusion of the septa that separated the two atria during development.
3. In which chamber of the heart is the fossa ovalis located?
a) Left atrium
b) Right atrium
c) Left ventricle
d) Right ventricle
Explanation (Answer: b) Right atrium)
The fossa ovalis is located in the right atrium on the interatrial septum. It is visible as a shallow oval depression below the limbus. On the left atrial side, it corresponds to a slight ridge. The fossa ovalis marks the site of the closed foramen ovale, a vital fetal shunt between the atria.
4. Which structure forms the floor of the fossa ovalis?
a) Septum secundum
b) Septum primum
c) Endocardial cushions
d) Sinus venosus
Explanation (Answer: b) Septum primum)
The floor of the fossa ovalis is derived from the septum primum. During fetal life, the septum primum acted as a valve over the foramen ovale. After birth, increased left atrial pressure pushes it against the septum secundum, leading to closure and eventual fusion, forming the interatrial septum in the adult heart.
5. A 2-year-old child presents with shortness of breath and cyanosis. Echocardiography reveals a patent foramen ovale. The defect is due to failure of fusion between:
a) Septum primum and endocardial cushions
b) Septum secundum and septum primum
c) Septum primum and interventricular septum
d) Septum secundum and sinus venosus
Explanation (Answer: b) Septum secundum and septum primum)
A patent foramen ovale results from the failure of fusion between the septum primum and septum secundum after birth. This causes persistence of interatrial communication, leading to shunting of blood and cyanosis. Unlike ASD, it is a functional defect, not a true septal deficiency.
6. Which of the following correctly represents the embryological derivation of the limbus fossa ovalis?
a) Septum primum
b) Septum secundum
c) Endocardial cushions
d) Common atrial wall
Explanation (Answer: b) Septum secundum)
The limbus fossa ovalis is derived from the septum secundum, which forms the thickened superior rim of the fossa ovalis in the right atrium. In contrast, the septum primum forms the floor of the fossa. This structure demarcates the site of the embryonic foramen ovale closure postnatally.
7. In fetal circulation, blood passes from right atrium to left atrium through:
a) Ductus venosus
b) Foramen ovale
c) Ductus arteriosus
d) Sinus venosus
Explanation (Answer: b) Foramen ovale)
In the fetus, oxygenated blood from the placenta enters the right atrium and passes through the foramen ovale into the left atrium, bypassing the nonfunctional lungs. After birth, rising left atrial pressure forces closure of the foramen, which later becomes the fossa ovalis in the adult heart.
8. A patient with an atrial septal defect has a defect in which structure?
a) Septum primum
b) Septum secundum
c) Both septum primum and secundum
d) Interventricular septum
Explanation (Answer: c) Both septum primum and secundum)
Atrial septal defects (ASD) often occur due to incomplete development or alignment of the septum primum and septum secundum. This results in an interatrial communication causing left-to-right shunt and increased pulmonary blood flow. Common types include ostium secundum and ostium primum defects, depending on location and extent of the gap.
9. In which condition does the foramen ovale remain patent, but the septa are normally developed?
a) Atrial septal defect
b) Patent foramen ovale
c) Endocardial cushion defect
d) Ventricular septal defect
Explanation (Answer: b) Patent foramen ovale)
In patent foramen ovale (PFO), the septum primum and septum secundum fail to fuse completely, even though both are structurally normal. This persistence allows potential right-to-left shunt under pressure changes, sometimes leading to paradoxical embolism without true septal tissue deficiency, distinguishing it from ASD.
10. A 5-year-old with a history of recurrent respiratory infections is found to have left-to-right shunt due to ostium secundum defect. The likely embryologic cause is:
a) Excessive resorption of septum primum
b) Underdevelopment of septum secundum
c) Both a and b
d) Fusion of septum primum and secundum
Explanation (Answer: c) Both a and b)
An ostium secundum ASD commonly results from excessive resorption of septum primum or underdevelopment of septum secundum. This leads to a persistent opening in the interatrial septum, causing a left-to-right shunt, increased pulmonary flow, and predisposition to respiratory infections and heart failure in children.
Chapter: Embryology; Topic: Development of Reproductive System; Subtopic: Origin and Function of Sertoli Cells
Keyword Definitions:
• Sertoli cells: Tall supporting cells in seminiferous tubules that nourish developing sperm and form the blood-testis barrier.
• Germinal epithelium: Layer of epithelial cells lining the primitive gonadal ridge giving rise to Sertoli and follicular cells.
• Primordial germ cells: Cells that give rise to spermatozoa and ova.
• Seminiferous tubules: Tubules within the testes where spermatogenesis occurs.
• Genital ridge: Embryonic structure forming the gonads.
• Genital tubercle: Embryonic swelling giving rise to external genitalia.
Lead Question - 2015
Sertoli cells are derived from -
a) Genital tubercle
b) Genital swelling
c) Primordial germ cells
d) Germinal epithelium
Explanation (Answer: d) Germinal epithelium)
Sertoli cells originate from the germinal epithelium (coelomic epithelium) of the developing gonadal ridge. They differentiate within seminiferous cords of the testis and play a vital role in spermatogenesis by providing nourishment and structural support. They also secrete Anti-Müllerian hormone (AMH), crucial for regression of Müllerian ducts in males.
1. Which of the following hormones is secreted by Sertoli cells?
a) Testosterone
b) Inhibin
c) LH
d) FSH
Explanation (Answer: b) Inhibin)
Sertoli cells secrete inhibin, a peptide hormone that provides negative feedback to the anterior pituitary to regulate FSH secretion. They also produce Androgen Binding Protein (ABP) to concentrate testosterone in seminiferous tubules, supporting spermatogenesis. Leydig cells, not Sertoli cells, secrete testosterone under LH stimulation.
2. The primary function of Sertoli cells in the seminiferous tubules is:
a) Secretion of testosterone
b) Nourishment and support of germ cells
c) Formation of seminal plasma
d) Production of sperm motility factors
Explanation (Answer: b) Nourishment and support of germ cells)
Sertoli cells are essential “nurse” cells that nourish, support, and protect developing spermatogenic cells. They form tight junctions creating the blood-testis barrier and phagocytose residual cytoplasm from spermatids. They also secrete inhibin, AMH, and ABP, maintaining a suitable microenvironment for spermatogenesis under FSH influence.
3. Which embryonic structure gives rise to Leydig cells in the testis?
a) Germinal epithelium
b) Mesenchyme of genital ridge
c) Wolffian duct
d) Paramesonephric duct
Explanation (Answer: b) Mesenchyme of genital ridge)
Leydig cells, the interstitial cells of the testis, originate from the mesenchyme of the genital ridge. They begin secreting testosterone around the 8th week of development, which is essential for differentiation of the male reproductive tract and external genitalia. Sertoli cells, by contrast, arise from the germinal epithelium.
4. Which hormone induces Sertoli cells to secrete Androgen Binding Protein (ABP)?
a) LH
b) FSH
c) Testosterone
d) Prolactin
Explanation (Answer: b) FSH)
FSH (Follicle Stimulating Hormone) acts on Sertoli cells, stimulating them to produce Androgen Binding Protein (ABP) that binds and concentrates testosterone in seminiferous tubules. This high local testosterone concentration is critical for spermatogenesis. LH acts on Leydig cells to produce testosterone, which synergizes with FSH in this process.
5. A newborn male with persistent Müllerian duct structures likely has a defect in secretion of:
a) Testosterone
b) Anti-Müllerian hormone
c) Inhibin
d) FSH
Explanation (Answer: b) Anti-Müllerian hormone)
Sertoli cells secrete Anti-Müllerian hormone (AMH) during fetal life, which causes regression of the paramesonephric (Müllerian) ducts. Deficiency or absence of AMH results in Persistent Müllerian Duct Syndrome (PMDS), where male individuals have remnants of uterus and fallopian tubes despite normal male external genitalia and karyotype (46, XY).
6. Which of the following cells form the blood-testis barrier?
a) Spermatogonia
b) Sertoli cells
c) Leydig cells
d) Myoid cells
Explanation (Answer: b) Sertoli cells)
Sertoli cells form the blood-testis barrier through tight junctions between adjacent cells, dividing the seminiferous tubule into basal and adluminal compartments. This barrier protects developing germ cells from autoimmune attack by preventing exposure of sperm antigens to the immune system while allowing selective nutrient exchange.
7. Damage to Sertoli cells would primarily affect which process?
a) Testosterone synthesis
b) Spermatogenesis
c) Epididymal transport
d) Seminal fluid secretion
Explanation (Answer: b) Spermatogenesis)
Sertoli cells are vital for spermatogenesis as they provide physical and nutritional support for germ cells, form the blood-testis barrier, and secrete growth factors essential for sperm development. Their injury disrupts the seminiferous epithelium, halting sperm maturation despite normal testosterone levels from Leydig cells.
8. A 22-year-old male presents with infertility despite normal testosterone. Which defect could explain this finding?
a) Dysfunction of Sertoli cells
b) Leydig cell hyperplasia
c) Pituitary tumor
d) Hypothalamic lesion
Explanation (Answer: a) Dysfunction of Sertoli cells)
Normal testosterone with infertility suggests defective Sertoli cell function. Sertoli cells support spermatogenesis, form the blood-testis barrier, and secrete ABP and inhibin. Their dysfunction impairs sperm maturation and leads to non-obstructive azoospermia. Leydig cells remain unaffected, explaining normal testosterone production.
9. Which of the following pairs is correctly matched?
a) Leydig cells – Blood-testis barrier
b) Sertoli cells – Androgen binding protein
c) Spermatogonia – Testosterone synthesis
d) Germinal epithelium – LH secretion
Explanation (Answer: b) Sertoli cells – Androgen binding protein)
Sertoli cells produce Androgen Binding Protein (ABP) in response to FSH stimulation. ABP binds testosterone and maintains high intratubular concentration necessary for spermatogenesis. Leydig cells synthesize testosterone, while spermatogonia are developing germ cells that rely on the Sertoli cell environment for maturation.
10. In a male infant with XY karyotype and persistence of Müllerian ducts, which gene or hormone deficiency is most likely?
a) AMH deficiency
b) Testosterone deficiency
c) LH receptor mutation
d) FSH receptor mutation
Explanation (Answer: a) AMH deficiency)
Persistence of Müllerian structures (uterus and fallopian tubes) in a genetic male indicates Anti-Müllerian hormone (AMH) deficiency or insensitivity. AMH, produced by fetal Sertoli cells, normally induces Müllerian duct regression. Its absence leads to Persistent Müllerian Duct Syndrome, despite normal androgen and external genital development.
Chapter: Embryology; Topic: Development of Endocrine System; Subtopic: Development of Pituitary Gland
Keyword Definitions:
• Rathke’s pouch: An ectodermal outpouching from the roof of the stomodeum forming the anterior pituitary (adenohypophysis).
• Infundibulum: A neuroectodermal downward extension from the diencephalon forming the posterior pituitary (neurohypophysis).
• Adenohypophysis: Anterior lobe of the pituitary that secretes hormones like prolactin, GH, and ACTH.
• Neurohypophysis: Posterior lobe of pituitary storing ADH and oxytocin from hypothalamic neurons.
• Tuber cinereum: Area of hypothalamus between optic chiasma and mammillary bodies controlling pituitary function.
• Prolactin: Hormone secreted by lactotrophs of adenohypophysis that stimulates milk production in females.
Lead Question - 2015
Prolactin secreting gland develops from -
a) Infundibulum
b) Rathke's pouch
c) Tuber cinereum
d) 3rd ventricle
Explanation (Answer: b) Rathke’s pouch)
The anterior pituitary (adenohypophysis), which secretes prolactin, develops from the Rathke’s pouch — an ectodermal diverticulum from the roof of the primitive mouth (stomodeum). The posterior lobe (neurohypophysis) originates from the infundibulum of the diencephalon. The gland later differentiates into secretory cells producing prolactin, GH, ACTH, and other trophic hormones.
1. The anterior lobe of the pituitary gland is derived from which embryonic germ layer?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neuroectoderm
Explanation (Answer: c) Ectoderm)
The adenohypophysis (anterior pituitary) originates from oral ectoderm of Rathke’s pouch. This ectodermal tissue grows upward from the roof of the primitive mouth and later detaches to form the anterior lobe. In contrast, the neurohypophysis arises from neuroectoderm of the diencephalon, forming a neural connection to the hypothalamus.
2. The posterior pituitary develops from which of the following structures?
a) Rathke’s pouch
b) Infundibulum
c) Tuber cinereum
d) Roof of stomodeum
Explanation (Answer: b) Infundibulum)
The neurohypophysis or posterior pituitary develops from the infundibular process, a downward projection of neuroectoderm from the diencephalon. It remains connected to the hypothalamus via the infundibular stalk and stores oxytocin and vasopressin, which are synthesized in the supraoptic and paraventricular nuclei of the hypothalamus.
3. Which of the following cells secrete prolactin in the anterior pituitary?
a) Somatotrophs
b) Corticotrophs
c) Lactotrophs
d) Thyrotrophs
Explanation (Answer: c) Lactotrophs)
Lactotrophs (mammotrophs) are the cells in the adenohypophysis responsible for prolactin secretion. Prolactin stimulates breast development and milk secretion. Its secretion is tonically inhibited by dopamine from the hypothalamus. During pregnancy and lactation, estrogen and TRH increase prolactin synthesis and release from these specialized cells.
4. Which of the following hormones is NOT secreted by the anterior pituitary?
a) ACTH
b) GH
c) Vasopressin
d) TSH
Explanation (Answer: c) Vasopressin)
Vasopressin (ADH) is secreted by the posterior pituitary (neurohypophysis), not the anterior lobe. The anterior pituitary secretes six major hormones—GH, ACTH, TSH, FSH, LH, and prolactin—all derived from ectoderm of Rathke’s pouch. ADH is synthesized in the hypothalamus and only stored in the posterior pituitary.
5. A patient with pituitary adenoma involving lactotrophs would most likely present with:
a) Hypothyroidism
b) Amenorrhea and galactorrhea
c) Cushing’s syndrome
d) Acromegaly
Explanation (Answer: b) Amenorrhea and galactorrhea)
Prolactin-secreting pituitary adenoma (prolactinoma) causes hyperprolactinemia leading to amenorrhea, galactorrhea, and infertility in females, and decreased libido in males. Prolactin suppresses GnRH secretion, reducing FSH and LH levels. Dopamine agonists like bromocriptine or cabergoline are used for medical management of prolactinomas.
6. The pituitary gland is located within which bony structure?
a) Sphenoid sinus
b) Hypophyseal fossa
c) Optic canal
d) Foramen magnum
Explanation (Answer: b) Hypophyseal fossa)
The pituitary gland resides in the hypophyseal fossa of the sella turcica in the sphenoid bone. This bony cavity protects the gland and is covered superiorly by the diaphragma sellae. The optic chiasma lies anterior and superior to it, making it prone to compression in pituitary tumors causing visual disturbances.
7. Which of the following statements about Rathke’s pouch is true?
a) It is derived from endoderm
b) Gives rise to posterior pituitary
c) It is an upward growth from stomodeum
d) It remains connected to the hypothalamus
Explanation (Answer: c) It is an upward growth from stomodeum)
Rathke’s pouch is an upward ectodermal outpouching from the roof of the stomodeum (primitive mouth) that forms the anterior lobe of the pituitary gland. It later detaches from the oral cavity and fuses with the downward-growing infundibulum from the diencephalon to form the complete pituitary gland.
8. A child with craniopharyngioma has a tumor derived from remnants of:
a) Infundibulum
b) Rathke’s pouch
c) Pineal gland
d) Optic chiasma
Explanation (Answer: b) Rathke’s pouch)
Craniopharyngioma is a benign tumor arising from remnants of Rathke’s pouch. It commonly occurs in children and young adults, presenting with headaches, visual disturbances, and growth retardation due to compression of the optic chiasma and pituitary gland. It contains calcifications and cystic areas with cholesterol-rich fluid.
9. Which hypothalamic nucleus is primarily responsible for prolactin inhibition?
a) Supraoptic nucleus
b) Paraventricular nucleus
c) Arcuate nucleus
d) Mammillary nucleus
Explanation (Answer: c) Arcuate nucleus)
The arcuate nucleus of the hypothalamus secretes dopamine (prolactin-inhibiting hormone) that inhibits prolactin secretion from lactotrophs of the anterior pituitary. Damage to this nucleus or dopaminergic pathways results in hyperprolactinemia. Dopamine agonists, such as bromocriptine, restore prolactin control in such cases.
10. A 45-year-old woman presents with bitemporal hemianopia and hyperprolactinemia. MRI shows a sellar mass. Which structure is compressed?
a) Optic chiasma
b) Internal capsule
c) Corpus callosum
d) Hypothalamus
Explanation (Answer: a) Optic chiasma)
A pituitary macroadenoma enlarging superiorly from the sella turcica compresses the optic chiasma, producing bitemporal hemianopia. It may also cause hormonal imbalances, including hyperprolactinemia due to lactotroph adenoma. Surgical decompression via trans-sphenoidal approach is the preferred treatment in such cases.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Development of Venous System
Keyword Definitions:
• Posterior cardinal veins: Paired embryonic veins that drain the body wall and lower part of the embryo; they are replaced by subcardinal and supracardinal veins later.
• Common iliac veins: Veins formed from the caudal portions of the posterior cardinal veins.
• Subcardinal veins: Veins forming parts of the inferior vena cava, renal, and gonadal veins.
• Supracardinal veins: Veins forming azygos and hemiazygos systems.
• Anterior cardinal veins: Form internal jugular and superior vena cava.
• Common cardinal veins: Short segments draining into the sinus venosus, forming part of the right atrium.
Lead Question - 2015
Posterior cardinal vein develops into -
a) Common iliac vein
b) Superior vena cava
c) Internal jugular vein
d) External jugular vein
Explanation (Answer: a) Common iliac vein)
The posterior cardinal veins are embryonic veins that initially drain the lower part of the body. Most of them regress during development, but their caudal portions persist as the common iliac veins. They are later replaced by the subcardinal and supracardinal systems, which contribute to the formation of the inferior vena cava and azygos veins.
1. The superior vena cava develops from which embryonic vein?
a) Anterior cardinal vein
b) Posterior cardinal vein
c) Subcardinal vein
d) Supracardinal vein
Explanation (Answer: a) Anterior cardinal vein)
The superior vena cava develops from the right anterior cardinal vein and the right common cardinal vein. The left anterior cardinal vein regresses except for its upper part, which forms the left brachiocephalic vein. The posterior cardinal veins do not contribute to the superior vena cava in the adult.
2. Which part of the inferior vena cava is derived from the posterior cardinal veins?
a) Hepatic segment
b) Prerenal segment
c) Renal segment
d) Postrenal segment
Explanation (Answer: d) Postrenal segment)
The postrenal segment of the inferior vena cava develops from the right supracardinal and posterior cardinal veins. The hepatic segment arises from the hepatic veins, the prerenal from the right subcardinal vein, and the renal from the subcardinal–supracardinal anastomosis. Thus, posterior cardinal veins contribute mainly to the lower (postrenal) IVC and common iliac veins.
3. Azygos vein develops from which embryonic vein?
a) Subcardinal vein
b) Supracardinal vein
c) Posterior cardinal vein
d) Common cardinal vein
Explanation (Answer: b) Supracardinal vein)
The azygos vein develops from the right supracardinal vein and drains the posterior thoracic wall. The left supracardinal vein forms the hemiazygos vein. The posterior cardinal veins largely regress, with only their caudal portions persisting as common iliac veins. The supracardinal system replaces the posterior cardinal veins in most regions.
4. Which embryonic structure gives rise to the renal veins?
a) Posterior cardinal veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: b) Subcardinal veins)
The renal veins develop from the subcardinal veins and the subcardinal–supracardinal anastomosis. These veins also form the gonadal veins and a part of the inferior vena cava. The posterior cardinal veins play only a minor transient role in the early embryonic venous drainage and are later replaced by subcardinal and supracardinal veins.
5. The internal jugular vein develops from which embryonic vein?
a) Anterior cardinal vein
b) Posterior cardinal vein
c) Subcardinal vein
d) Supracardinal vein
Explanation (Answer: a) Anterior cardinal vein)
The internal jugular veins develop from the anterior cardinal veins, which drain the cranial part of the embryo. The left anterior cardinal vein contributes to the left brachiocephalic vein, while the right forms part of the superior vena cava. Posterior cardinal veins drain the caudal regions and are not involved in jugular formation.
6. A neonate with an absent inferior vena cava below the renal veins likely has developmental failure of which embryonic structure?
a) Hepatic veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: c) Supracardinal veins)
The supracardinal veins form the postrenal segment of the inferior vena cava. Failure of their development results in absence of IVC below the renal veins. In such cases, venous return from the lower limbs occurs through the azygos and hemiazygos systems, compensating for the absent lower IVC segment.
7. Which embryonic vein forms the hemiazygos vein?
a) Left supracardinal vein
b) Right subcardinal vein
c) Left posterior cardinal vein
d) Right common cardinal vein
Explanation (Answer: a) Left supracardinal vein)
The hemiazygos vein develops from the left supracardinal vein. It drains the lower left posterior thoracic wall and crosses to join the azygos vein. The right supracardinal vein forms the azygos system, while the posterior cardinal veins regress, except for their caudal ends forming common iliac veins.
8. The left brachiocephalic vein is formed by an anastomosis between:
a) Subcardinal veins
b) Anterior cardinal veins
c) Posterior cardinal veins
d) Common cardinal veins
Explanation (Answer: b) Anterior cardinal veins)
The left brachiocephalic vein forms from a transverse anastomosis between the left and right anterior cardinal veins. Blood from the left head and neck drains through this vein into the right anterior cardinal system, which forms the superior vena cava. This anastomosis compensates for regression of the caudal part of the left anterior cardinal vein.
9. Which of the following venous anomalies occurs due to persistence of the left anterior cardinal vein?
a) Double superior vena cava
b) Absent azygos vein
c) Interrupted IVC
d) Persistent ductus venosus
Explanation (Answer: a) Double superior vena cava)
Persistence of the left anterior cardinal vein results in a double superior vena cava. Normally, the caudal part of this vein regresses during development. When it persists, venous blood from the left side drains into the coronary sinus rather than joining the right superior vena cava, creating a dual drainage system.
10. A 6-year-old boy has congenital absence of common iliac veins. Which embryonic structure failed to develop properly?
a) Posterior cardinal veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: a) Posterior cardinal veins)
The common iliac veins develop from the caudal portions of the posterior cardinal veins. Failure of their development leads to congenital absence of these veins, resulting in alternate pelvic venous drainage through collateral pathways. The posterior cardinal system is transient but crucial for forming iliac and early systemic venous segments.
Chapter: Embryology; Topic: Development of Cardiovascular System; Subtopic: Development of Venous System
Keyword Definitions:
• Superior vena cava (SVC): Large systemic vein returning deoxygenated blood from the head, neck, and upper limbs to the right atrium.
• Anterior cardinal veins: Paired embryonic veins that drain the cranial portion of the embryo.
• Common cardinal veins: Short venous trunks connecting anterior and posterior cardinal veins to the sinus venosus.
• Subcardinal veins: Veins forming part of the inferior vena cava, renal, and gonadal veins.
• Supracardinal veins: Veins that form the azygos and hemiazygos systems.
• Sinus venosus: Primitive venous chamber that becomes incorporated into the right atrium during cardiac development.
Lead Question - 2015
Superior vena cava develops from -
a) Right anterior cardinal vein
b) Left anterior cardinal vein
c) Left common cardinal vein
d) Right subcardinal vein
Explanation (Answer: a) Right anterior cardinal vein)
The superior vena cava (SVC) develops from the right anterior cardinal vein and the right common cardinal vein. The left anterior cardinal vein largely regresses, with its remnant forming part of the left brachiocephalic vein. The SVC drains blood from the head, neck, and upper limbs into the right atrium. Abnormal persistence of the left anterior cardinal vein can result in a double SVC anomaly.
1. The left brachiocephalic vein develops from which embryonic structure?
a) Right anterior cardinal vein
b) Left posterior cardinal vein
c) Left anterior cardinal vein
d) Subcardinal vein
Explanation (Answer: c) Left anterior cardinal vein)
The left brachiocephalic vein develops from the left anterior cardinal vein and an anastomosis between the right and left anterior cardinal veins. This allows blood from the left head and upper limb to drain into the right-sided SVC. Regression of the left common cardinal vein and persistence of this connection create the left brachiocephalic vein.
2. Which of the following embryonic veins forms the azygos vein?
a) Right supracardinal vein
b) Right subcardinal vein
c) Right posterior cardinal vein
d) Left anterior cardinal vein
Explanation (Answer: a) Right supracardinal vein)
The azygos vein develops from the right supracardinal vein. This vein drains the posterior thoracic wall and joins the superior vena cava near its termination. The left supracardinal vein forms the hemiazygos vein, while posterior cardinal veins regress and are replaced by the supracardinal and subcardinal systems during embryonic development.
3. The inferior vena cava (IVC) is formed from all except:
a) Hepatic veins
b) Subcardinal veins
c) Posterior cardinal veins
d) Anterior cardinal veins
Explanation (Answer: d) Anterior cardinal veins)
The inferior vena cava (IVC) is formed from the hepatic veins, subcardinal veins, supracardinal veins, and posterior cardinal veins, but not from the anterior cardinal veins. The anterior cardinal veins contribute to the superior venous system, including the internal jugular veins and the superior vena cava, not the IVC.
4. Which embryonic vein forms the internal jugular veins?
a) Anterior cardinal vein
b) Posterior cardinal vein
c) Subcardinal vein
d) Common cardinal vein
Explanation (Answer: a) Anterior cardinal vein)
The anterior cardinal veins form the internal jugular veins, which drain the cranial part of the embryo. The right anterior cardinal vein and common cardinal vein later form the superior vena cava, while the left anterior cardinal vein contributes to the left brachiocephalic vein through anastomotic connections.
5. Which of the following anomalies results from persistence of the left anterior cardinal vein?
a) Double superior vena cava
b) Absent inferior vena cava
c) Azygos continuation
d) Persistent ductus venosus
Explanation (Answer: a) Double superior vena cava)
Persistence of the left anterior cardinal vein results in the formation of a double superior vena cava. Normally, this vein regresses, and its blood drains into the right side through the left brachiocephalic vein. When it persists, a second SVC is formed on the left, typically draining into the coronary sinus.
6. The right common cardinal vein contributes to which adult structure?
a) Coronary sinus
b) Superior vena cava
c) Inferior vena cava
d) Azygos vein
Explanation (Answer: b) Superior vena cava)
The right common cardinal vein, along with the right anterior cardinal vein, forms the superior vena cava. The left common cardinal vein and the left sinus horn form the coronary sinus. The common cardinal veins act as the final venous channels draining into the primitive sinus venosus during embryogenesis.
7. The coronary sinus develops from which embryonic structure?
a) Right anterior cardinal vein
b) Left common cardinal vein
c) Left posterior cardinal vein
d) Right subcardinal vein
Explanation (Answer: b) Left common cardinal vein)
The coronary sinus develops from the left common cardinal vein and the left sinus horn. This structure persists in the adult heart as the main venous channel draining the myocardium into the right atrium. The regression of the left-sided systemic venous channels leaves the coronary sinus as a vestige of the left venous system.
8. A 3-year-old child presents with cyanosis and venous drainage from left upper limb directly into the coronary sinus. The cause is:
a) Persistent left anterior cardinal vein
b) Absent right anterior cardinal vein
c) Persistent left common cardinal vein
d) Absent right common cardinal vein
Explanation (Answer: a) Persistent left anterior cardinal vein)
Persistence of the left anterior cardinal vein leads to venous drainage from the left upper limb and head directly into the coronary sinus. This anomaly produces a left-sided superior vena cava. It is usually asymptomatic but may complicate cardiac catheterization or pacemaker insertion due to the altered venous route.
9. The azygos and hemiazygos veins develop from:
a) Posterior cardinal veins
b) Subcardinal veins
c) Supracardinal veins
d) Common cardinal veins
Explanation (Answer: c) Supracardinal veins)
The supracardinal veins develop to replace the posterior cardinal veins and form the azygos (right) and hemiazygos (left) veins. These veins drain the posterior thoracic wall and intercostal spaces. The posterior cardinal veins regress except for their caudal parts, which persist as the common iliac veins.
10. A newborn has absence of superior vena cava on the right, with drainage of head and neck veins into the coronary sinus. This condition is due to:
a) Regression of right anterior cardinal vein
b) Regression of left anterior cardinal vein
c) Persistence of right subcardinal vein
d) Persistence of left supracardinal vein
Explanation (Answer: a) Regression of right anterior cardinal vein)
Absence of the right superior vena cava occurs due to regression of the right anterior cardinal vein and persistence of the left anterior cardinal vein, which drains into the coronary sinus. This creates a left-sided superior vena cava, an uncommon venous anomaly seen in some congenital heart defects.
Chapter: Embryology; Topic: Development of Reproductive System; Subtopic: Derivatives of Mesonephric and Paramesonephric Ducts
Keyword Definitions:
• Müllerian duct (Paramesonephric duct): Embryonic structure that develops into the female reproductive tract (uterus, fallopian tubes, upper vagina) and regresses in males.
• Wolffian duct (Mesonephric duct): Embryonic structure that develops into male genital ducts (epididymis, vas deferens, seminal vesicle).
• Prostatic utricle: A small pouch in males derived from the Müllerian duct; homologous to the uterus and vagina.
• Anti-Müllerian hormone (AMH): Hormone secreted by Sertoli cells in males that causes regression of Müllerian ducts.
• Appendix testis: Vestigial Müllerian remnant at the superior pole of the testis.
• Mesonephric tubules: Give rise to efferent ductules of the testes.
Lead Question - 2015
Structure developing from Müllerian duct in males?
a) Seminal vesicle
b) Epididymis
c) Prostatic utricle
d) Ureter
Explanation (Answer: c) Prostatic utricle)
In males, the Müllerian ducts regress under the influence of Anti-Müllerian hormone (AMH) secreted by Sertoli cells. However, small remnants persist, forming the prostatic utricle and appendix testis. The prostatic utricle is a small blind sac opening into the prostatic urethra and represents the male homologue of the uterus and vagina.
1. Which of the following structures is derived from the Müllerian duct in females?
a) Seminal vesicle
b) Fallopian tube
c) Epididymis
d) Prostatic utricle
Explanation (Answer: b) Fallopian tube)
In females, the Müllerian (paramesonephric) ducts develop into the uterine tubes (fallopian tubes), uterus, and upper part of the vagina. This occurs due to the absence of AMH. In males, these ducts regress except for remnants like the appendix testis and prostatic utricle. Their normal fusion forms the midline uterine structure.
2. The mesonephric duct in males develops into which of the following?
a) Uterus
b) Vas deferens
c) Fallopian tube
d) Upper vagina
Explanation (Answer: b) Vas deferens)
The mesonephric (Wolffian) duct develops into male genital ducts including the epididymis, vas deferens, seminal vesicle, and ejaculatory duct. Testosterone secreted by Leydig cells promotes their differentiation, while Anti-Müllerian hormone from Sertoli cells suppresses paramesonephric duct development in males.
3. A small cyst near the prostate in a male child most likely represents a remnant of which embryonic structure?
a) Müllerian duct
b) Mesonephric duct
c) Ureteric bud
d) Allantois
Explanation (Answer: a) Müllerian duct)
A cyst near the prostate represents a prostatic utricle cyst, derived from the Müllerian duct. It is a remnant of embryonic female reproductive tract structures that failed to regress completely in males. Large cysts may cause urinary obstruction or infection but are typically benign and asymptomatic.
4. Which hormone causes regression of the Müllerian ducts in male embryos?
a) Testosterone
b) Anti-Müllerian hormone
c) Estrogen
d) Progesterone
Explanation (Answer: b) Anti-Müllerian hormone)
Anti-Müllerian hormone (AMH) is secreted by Sertoli cells of the fetal testes and induces regression of the Müllerian ducts, preventing the formation of female internal genital organs in males. In its absence, structures such as the uterus and fallopian tubes may persist, leading to Persistent Müllerian Duct Syndrome (PMDS).
5. Persistent Müllerian Duct Syndrome (PMDS) in a male is caused by deficiency of which of the following?
a) Testosterone
b) Anti-Müllerian hormone
c) LH
d) FSH
Explanation (Answer: b) Anti-Müllerian hormone)
PMDS is a rare condition in which Müllerian duct structures (uterus and fallopian tubes) persist in males with normal external genitalia. It occurs due to a deficiency or insensitivity to Anti-Müllerian hormone (AMH) or its receptor. The condition may present as undescended testes or inguinal hernia containing uterine tissue.
6. The epididymis is derived from which embryonic structure?
a) Müllerian duct
b) Mesonephric duct
c) Paramesonephric duct
d) Cloaca
Explanation (Answer: b) Mesonephric duct)
The epididymis originates from the mesonephric duct under the influence of testosterone secreted by Leydig cells. This duct elongates and becomes coiled, forming the epididymal structure. The Müllerian duct, in contrast, regresses in males due to AMH, leaving only small remnants like the appendix testis.
7. In females, failure of fusion of Müllerian ducts leads to which congenital anomaly?
a) Bicornuate uterus
b) Uterine agenesis
c) Vaginal atresia
d) Septate uterus
Explanation (Answer: a) Bicornuate uterus)
A bicornuate uterus occurs when the Müllerian ducts fail to fuse completely during embryonic development, resulting in a uterus with two horns. Other fusion defects include didelphys uterus and septate uterus. These anomalies may cause recurrent miscarriage or infertility, highlighting the importance of normal ductal fusion in female reproductive development.
8. Which of the following male structures represents a Müllerian remnant?
a) Appendix epididymis
b) Appendix testis
c) Vas deferens
d) Seminal vesicle
Explanation (Answer: b) Appendix testis)
The appendix testis is a small pedunculated structure attached to the superior pole of the testis and represents a Müllerian duct remnant. It may undergo torsion, causing acute scrotal pain in children. In contrast, the appendix epididymis is derived from the mesonephric duct, not the Müllerian duct.
9. Which of the following is NOT derived from the Müllerian duct?
a) Uterus
b) Fallopian tubes
c) Upper vagina
d) Labia majora
Explanation (Answer: d) Labia majora)
The labia majora are derived from the genital swellings, not the Müllerian ducts. The Müllerian ducts give rise to the fallopian tubes, uterus, and the upper part of the vagina. The lower vagina develops from the urogenital sinus, which fuses with the Müllerian ducts during embryogenesis.
10. A male newborn with cryptorchidism and uterus-like structure in the pelvis likely has:
a) Persistent Müllerian Duct Syndrome
b) Klinefelter syndrome
c) Androgen insensitivity syndrome
d) Testicular feminization
Explanation (Answer: a) Persistent Müllerian Duct Syndrome)
Persistent Müllerian Duct Syndrome (PMDS) is seen in males (46, XY) with normal external genitalia but persistent Müllerian derivatives due to lack of Anti-Müllerian hormone (AMH) or receptor defects. It may present with cryptorchidism or inguinal hernia containing a uterus or fallopian tube. Testosterone levels are usually normal in such cases.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of Ocular Layers and Optic Cup Formation
Keyword Definitions:
• Optic vesicle: Outgrowth from the forebrain (diencephalon) that gives rise to the optic cup and optic stalk.
• Optic cup: Double-layered structure derived from neural ectoderm that forms the retina and iris epithelium.
• Neural ectoderm: Ectodermal tissue of neural origin giving rise to CNS structures, including retina and optic nerve.
• Surface ectoderm: External ectodermal layer forming lens, corneal epithelium, and eyelids.
• Mesoderm: Middle germ layer contributing to extraocular muscles and vascular components of the eye.
• Neural crest cells: Migratory cells contributing to choroid, sclera, and corneal endothelium.
Lead Question - 2015
Optic cup is derived from?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation (Answer: a) Neural ectoderm)
The optic cup develops as an invagination of the optic vesicle, which itself is derived from the neural ectoderm of the forebrain (diencephalon). It forms a double-walled cup whose inner layer develops into the neural retina and outer layer into the retinal pigment epithelium (RPE). Thus, neural ectoderm gives rise to the essential sensory components of the eye.
1. The lens of the eye develops from which embryonic layer?
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Endoderm
Explanation (Answer: b) Surface ectoderm)
The lens develops from the surface ectoderm overlying the optic vesicle. The optic vesicle induces the ectoderm to form a lens placode, which invaginates to form the lens vesicle. This lens later differentiates into lens fibers. Neural ectoderm forms the retina, whereas mesoderm and neural crest form supportive structures like sclera and choroid.
2. The retinal pigment epithelium (RPE) of the eye develops from:
a) Surface ectoderm
b) Neural crest
c) Outer layer of optic cup
d) Mesoderm
Explanation (Answer: c) Outer layer of optic cup)
The outer layer of the optic cup, derived from neural ectoderm, forms the retinal pigment epithelium (RPE). The inner layer forms the neural retina. Together, these layers constitute the optic cup. The RPE plays a critical role in photoreceptor maintenance and absorption of scattered light, essential for visual clarity.
3. The corneal epithelium is derived from:
a) Neural ectoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest cells
Explanation (Answer: b) Surface ectoderm)
The corneal epithelium develops from the surface ectoderm, while the corneal stroma and endothelium arise from neural crest cells. The cornea forms the transparent anterior part of the eye, essential for refraction. The multi-layered epithelium ensures barrier protection and contributes to optical clarity through constant regeneration.
4. The optic nerve is derived from which embryonic structure?
a) Neural crest
b) Neural ectoderm of optic stalk
c) Surface ectoderm
d) Mesoderm
Explanation (Answer: b) Neural ectoderm of optic stalk)
The optic nerve develops from the optic stalk, an extension of the diencephalon derived from neural ectoderm. It contains axons of retinal ganglion cells that connect the retina to the brain. Unlike typical peripheral nerves, the optic nerve is part of the central nervous system and is surrounded by meninges.
5. A newborn with congenital blindness due to retinal aplasia has a developmental defect involving:
a) Neural crest
b) Surface ectoderm
c) Neural ectoderm
d) Mesoderm
Explanation (Answer: c) Neural ectoderm)
The retina develops from the neural ectoderm of the optic cup. Retinal aplasia occurs when this neural tissue fails to differentiate properly, resulting in loss of visual photoreceptors and functional blindness. Other ocular tissues like the cornea and lens may remain unaffected, depending on the extent of neural developmental failure.
6. The iris muscles (sphincter and dilator pupillae) are derived from:
a) Mesoderm
b) Neural crest
c) Neural ectoderm
d) Surface ectoderm
Explanation (Answer: c) Neural ectoderm)
Both the sphincter and dilator pupillae muscles are derived from the neural ectoderm of the optic cup. These are unique smooth muscles of ectodermal origin. They control pupillary size and regulate light entry into the eye. This is an exception since most smooth muscles arise from mesodermal origin in the body.
7. The sclera and choroid of the eye primarily develop from:
a) Surface ectoderm
b) Neural crest cells
c) Mesoderm
d) Neural ectoderm
Explanation (Answer: b) Neural crest cells)
The sclera and choroid develop from neural crest cells, which migrate around the optic cup. The sclera forms the dense fibrous protective covering of the eye, while the choroid forms the vascular layer providing oxygen and nutrients to the retina. Defects in neural crest migration may lead to anterior segment dysgenesis.
8. The hyaloid artery in fetal life is responsible for supplying which developing structure?
a) Retina
b) Cornea
c) Lens
d) Optic nerve
Explanation (Answer: c) Lens)
During fetal life, the hyaloid artery, a branch of the ophthalmic artery, supplies the developing lens and vitreous body. It later regresses, leaving behind the central artery of the retina. Persistence of the hyaloid artery after birth may form a vitreous opacity known as Mittendorf’s dot.
9. Coloboma of the iris results from defective closure of which structure?
a) Optic fissure
b) Optic vesicle
c) Lens vesicle
d) Corneal groove
Explanation (Answer: a) Optic fissure)
Coloboma of the iris results from failure of closure of the optic fissure during development of the optic cup. It appears as a keyhole defect in the iris. Depending on the extent, the defect may involve the retina or optic nerve, leading to varying degrees of visual impairment or blindness.
10. A baby is born with anophthalmos (absence of eyes). The most likely embryologic defect involves failure of:
a) Optic vesicle formation
b) Lens placode development
c) Hyaloid vessel regression
d) Optic fissure closure
Explanation (Answer: a) Optic vesicle formation)
Anophthalmos occurs due to complete failure of optic vesicle formation from the forebrain. This prevents induction of the lens placode and subsequent optic cup development. The condition leads to total absence of ocular tissue within the orbit and may be associated with severe cranial or neural tube malformations.