Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 211: Glomus cells are derived from which germ layer?

A. Surface ectoderm
B. Neuroectoderm (Correct Answer)
C. Mesoderm
D. Endoderm

Explanation: The correct answer is **Neuroectoderm**. Glomus cells (specifically Type I cells found in the carotid and aortic bodies) are specialized chemoreceptors responsible for sensing changes in blood $PO_2$, $PCO_2$, and pH. Embryologically, these cells are derived from the **Neural Crest Cells**, which are a specialized population of cells originating from the **neuroectoderm** at the margins of the neural tube [1]. Because neural crest cells migrate to various locations to form diverse structures, glomus cells are considered "neuroendocrine" in nature. **Analysis of Incorrect Options:** * **Surface Ectoderm:** This layer gives rise to the epidermis, hair, nails, and the anterior pituitary (Rathke’s pouch). It does not contribute to the formation of autonomic or sensory ganglia/chemoreceptors. * **Mesoderm:** While the connective tissue and blood vessels surrounding the glomus bodies are mesodermal in origin, the functional parenchymal cells (glomus cells) are neural crest-derived. * **Endoderm:** This layer forms the epithelial lining of the gastrointestinal and respiratory tracts. While the carotid body is located near the third pharyngeal arch (an endodermal structure), the cells themselves migrate from the neural crest. **High-Yield Clinical Pearls for NEET-PG:** * **Glomus Tumors (Paragangliomas):** These are highly vascular tumors arising from these cells. A common example is the **Carotid Body Tumor**, which typically presents as a painless neck mass that is mobile horizontally but not vertically (Fontaine’s sign). * **Zuckerkandl’s Organ:** The largest collection of extra-adrenal chromaffin tissue (also neural crest-derived), located near the origin of the inferior mesenteric artery. * **Rule of 10s:** Often associated with Pheochromocytomas (also derived from neural crest cells) [1].

Question 212: Which structure develops from the neural crest?

A. Enamel of tooth
B. Thoracic duct
C. Adrenal medulla (Correct Answer)
D. Spinal nerves

Explanation: **Explanation:** The **Neural Crest Cells (NCCs)** are often referred to as the "fourth germ layer" because of their multipotency and extensive migration. During neurulation, these cells detach from the lateral margins of the neural plate and migrate throughout the body to differentiate into various tissues. 1. **Why Adrenal Medulla is Correct:** The adrenal medulla is essentially a modified sympathetic ganglion [1]. Neural crest cells migrate to the dorsal abdomen to form **chromaffin cells**, which secrete catecholamines (epinephrine and norepinephrine) [2]. This explains why the adrenal medulla is functionally linked to the sympathetic nervous system. 2. **Analysis of Incorrect Options:** * **Enamel of tooth:** This is derived from the **Surface Ectoderm** (specifically the ameloblasts). Note: Most other dental structures like dentin, pulp, and cementum *are* neural crest-derived (ectomesenchyme). * **Thoracic duct:** This is a lymphatic structure derived from the **Mesoderm**. * **Spinal nerves:** This is a "trick" option. While the **Sensory ganglia** (Dorsal Root Ganglia) and **Schwann cells** of spinal nerves are neural crest-derived, the motor fibers of spinal nerves originate from the **Neural Tube** (neuroectoderm). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for NCC derivatives:** "MOTEL PASS" (Melanocytes, Odontoblasts, Tracheal cartilage, Enteric ganglia, Leptomeninges, Pia/Arachnoid, Adrenal medulla, Schwann cells, Sensory ganglia). * **Skull Development:** The bones of the **viscerocranium** (face) and parts of the neurocranium (frontal/sphenoid) are neural crest derivatives, whereas the occipital bone is paraxial mesoderm. * **Clinical Correlation:** Defects in NCC migration lead to **Neurocristopathies**, such as **Hirschsprung disease** (failure of enteric ganglia) and **DiGeorge Syndrome**.

Question 213: Which of the following is NOT a derivative of Rathke's pouch?

A. Pars intermedia
B. Pars tuberalis
C. Neurohypophysis (Correct Answer)
D. Pars distalis

Explanation: ### Explanation The pituitary gland (hypophysis) has a dual embryological origin, arising from two distinct ectodermal sources. Understanding this distinction is crucial for NEET-PG. **1. Why Neurohypophysis is the Correct Answer:** The **Neurohypophysis** (posterior pituitary) is derived from **neuroectoderm**. It develops as a downward extension (infundibulum) from the floor of the diencephalon (forebrain) [1]. Because it originates from the brain, it remains connected to the hypothalamus via the pituitary stalk. **2. Why the other options are incorrect:** Options A, B, and D are all derivatives of **Rathke’s pouch**, which is an upward ectodermal outpocketing of the **stomodeum** (primitive oral cavity). * **Pars distalis (D):** Forms the anterior lobe (adenohypophysis). * **Pars tuberalis (B):** An extension of the anterior lobe that wraps around the infundibular stalk. * **Pars intermedia (A):** The part of the pouch that contacts the neurohypophysis; it becomes rudimentary in humans [1]. **Clinical Pearls & High-Yield Facts:** * **Craniopharyngioma:** A tumor arising from the remnants of Rathke’s pouch. It is the most common suprasellar tumor in children and often shows calcification on imaging. * **Pharyngeal Pituitary:** Occasionally, a remnant of Rathke’s pouch persists in the roof of the pharynx. * **Rathke’s Cleft Cyst:** Occurs if the lumen of the pouch (the Rathke’s cleft) fails to obliterate, located between the anterior and posterior lobes. * **Master Mnemonic:** **A**denohypophysis = **A**limentary (Oral ectoderm); **N**eurohypophysis = **N**eural ectoderm.

Question 214: All of the following structures are derived from the mesonephric duct, except:

A. Vas deferens
B. Ureter
C. Trigone of urinary bladder
D. Prostatic utricle (Correct Answer)

Explanation: **Explanation:** The **Mesonephric (Wolffian) duct** is the precursor to the male internal genital structures. Its development is stimulated by testosterone produced by fetal Leydig cells. **Why the Prostatic Utricle is the correct answer:** The **prostatic utricle** is a small, blind-ending pouch in the prostatic urethra. It is a vestigial remnant of the **Paramesonephric (Müllerian) duct** in males [2]. Under the influence of Anti-Müllerian Hormone (AMH) from Sertoli cells, the Müllerian ducts regress [2], leaving behind only the prostatic utricle and the appendix testis. Therefore, it is not derived from the mesonephric duct. **Analysis of Incorrect Options:** * **Vas deferens:** This is a direct derivative of the mesonephric duct, which elongates and acquires a muscular coat to transport sperm [2]. * **Ureter:** The **ureteric bud** arises as a diverticulum from the caudal end of the mesonephric duct. It eventually gives rise to the ureter, renal pelvis, calyces, and collecting ducts. * **Trigone of urinary bladder:** The caudal ends of the mesonephric ducts are incorporated into the posterior wall of the urogenital sinus, forming the **mesodermal** trigone [1]. (Note: While the rest of the bladder is endodermal, the trigone is initially mesodermal, though later replaced by endodermal epithelium). **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Wolffian Derivatives (SEED):** **S**eminal vesicles, **E**pididymis, **E**jaculatory duct, and **D**uctus (Vas) deferens. 2. **Appendix Testis:** Another male remnant of the Paramesonephric duct. 3. **Gartner’s Cyst:** A female remnant of the Mesonephric duct found in the vaginal wall. 4. **Sertoli cells** produce AMH (regresses Müllerian ducts); **Leydig cells** produce Testosterone (stimulates Wolffian ducts) [2].

Question 215: A congenital diaphragmatic hernia may result from failure of which embryonic structure or event?

A. Septum transversum development
B. Fusion of pleuroperitoneal membranes (Correct Answer)
C. Complete development of the pleuropericardial membrane
D. Development of the dorsal mesentery of the esophagus

Explanation: ### Explanation Congenital Diaphragmatic Hernia (CDH) occurs due to a defect in the formation or fusion of the components that constitute the adult diaphragm. **Why Option B is Correct:** The diaphragm develops from four embryonic sources: the **septum transversum**, **pleuroperitoneal membranes**, **dorsal mesentery of the esophagus**, and **muscular ingrowths from the body wall**. The most common cause of CDH (specifically the **Bochdalek hernia**) is the failure of the **pleuroperitoneal membranes** to fuse with the other components, particularly the septum transversum and the dorsal mesentery. This leaves a persistent opening (the pleuroperitoneal canal) through which abdominal viscera herniate into the thoracic cavity. **Why Other Options are Incorrect:** * **Option A:** The septum transversum forms the **central tendon** of the diaphragm. While essential, its primary failure usually leads to different midline defects rather than the classic posterolateral hernia. * **Option C:** The **pleuropericardial membranes** are involved in separating the pericardial cavity from the pleural cavities and form the fibrous pericardium; they do not contribute to the diaphragm. * **Option D:** The dorsal mesentery of the esophagus forms the **crura** of the diaphragm. While it is a component, its isolated failure is not the primary cause of typical CDH. **High-Yield Clinical Pearls for NEET-PG:** * **Bochdalek Hernia:** The most common type (95%); occurs **posterolaterally** [2]. * **Side Predilection:** More common on the **Left side** (80-85%) because the left pleuroperitoneal canal closes later than the right, and the liver provides a physical barrier on the right [3]. * **Clinical Presentation:** Scaphoid abdomen, respiratory distress [1], and shifted heart sounds. * **Main Complication:** **Pulmonary hypoplasia** (due to compression by herniated viscera), which is the primary cause of mortality [1], [2]. * **Morgagni Hernia:** A rarer type occurring **anteriorly** through the retrosternal space.

Question 216: A double aortic arch is due to persistence and continued patency of which segment?

A. Right dorsal aorta between the right seventh intersegmental artery and its junction with the left dorsal aorta (Correct Answer)
B. Right dorsal aorta between the right sixth intersegmental artery and its junction with the left dorsal aorta
C. Left dorsal aorta between the right seventh intersegmental artery and its junction with the left dorsal aorta
D. Left dorsal aorta between the right sixth intersegmental artery and its junction with the left dorsal aorta

Explanation: ### Explanation **Concept Overview:** In normal embryonic development, the **right dorsal aorta** regresses between the origin of the right 7th intersegmental artery and its junction with the left dorsal aorta. This regression allows the formation of a single left-sided aortic arch. If this specific segment fails to regress and remains patent, both the right and left dorsal aortae persist, resulting in a **Double Aortic Arch**. **Why Option A is Correct:** The double aortic arch is a vascular ring anomaly. It occurs when the **distal portion of the right dorsal aorta** (located between the right 7th intersegmental artery and the point where the two dorsal aortae fuse to form the descending aorta) persists. This creates a ring of vessels that encircles and compresses the trachea and esophagus [1]. **Why Other Options are Incorrect:** * **Options B & D:** The **6th intersegmental artery** is not the landmark for the regression of the dorsal aorta; the 7th intersegmental artery is the crucial landmark as it eventually forms the subclavian artery. * **Options C & D:** The **Left dorsal aorta** normally persists to form the definitive aortic arch. Its regression would lead to a right-sided aortic arch, not a double aortic arch. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Double aortic arch is the most common cause of a symptomatic **vascular ring** [1]. It presents with "Stridor" (tracheal compression) and "Dysphagia lusoria" (esophageal compression) [1]. * **Radiology:** On a Barium swallow, it shows **bilateral indentations** on the esophagus [1]. * **Derivatives:** * **3rd Arch:** Common Carotid and proximal Internal Carotid. * **4th Arch:** Left forms the Aortic Arch; Right forms the proximal Right Subclavian. * **6th Arch:** Left forms the Ductus Arteriosus and Pulmonary Artery; Right forms the Pulmonary Artery.

Question 217: The tongue develops from all of the following except:

A. Lingual swellings
B. Tuberculum impar
C. Hypobranchial eminence
D. Frontonasal process (Correct Answer)

Explanation: The tongue develops from the floor of the primitive pharynx, specifically from the **pharyngeal arches (1st to 4th)**. The **Frontonasal process** is the correct answer because it contributes to the development of the forehead, bridge of the nose, and the primary palate, but has no role in tongue formation. ### Breakdown of Tongue Development: * **Lingual swellings (Option A):** Two lateral lingual swellings arise from the **1st pharyngeal arch**. They fuse to form the **anterior 2/3rd** (oral part) of the tongue. * **Tuberculum impar (Option B):** A median swelling from the **1st pharyngeal arch**. While it is eventually overgrown by the lateral lingual swellings, it is a primary embryological precursor of the tongue. * **Hypobranchial eminence (Option C):** Also known as the copula of His, it is formed by the mesoderm of the **3rd and 4th arches**. It gives rise to the **posterior 1/3rd** (pharyngeal part) of the tongue. ### NEET-PG High-Yield Pearls: 1. **Nerve Supply Rule:** The complex development explains the nerve supply. [1] * **Anterior 2/3:** Mandibular nerve (General sense) and Chorda tympani (Taste). [1] * **Posterior 1/3:** Glossopharyngeal nerve (Both general and taste). [1] 2. **Muscles:** All muscles of the tongue (except Palatoglossus) develop from **occipital myotomes** and are supplied by the **Hypoglossal nerve (CN XII)**. 3. **Foramen Caecum:** This represents the site of the original attachment of the thyroglossal duct, located at the junction of the anterior 2/3 and posterior 1/3.

Question 218: In a fetus, in which location is the highest oxygen concentration found?

A. Superior vena cava (SVC)
B. Inferior vena cava (IVC) (Correct Answer)
C. Right ventricle
D. Aorta (ascending)

Explanation: In fetal circulation, the oxygenation process differs significantly from postnatal life because the lungs are non-functional and the placenta serves as the organ of gas exchange. **1. Why Inferior Vena Cava (IVC) is Correct:** Oxygenated blood (approx. 80% saturated) leaves the placenta via the **umbilical vein** [1]. This blood enters the fetal body and mostly bypasses the liver through the **ductus venosus** to join the **Inferior Vena Cava (IVC)** [1]. Consequently, the IVC carries a mixture of highly oxygenated blood from the ductus venosus and deoxygenated blood from the lower limbs [1]. Despite this mixing, the IVC maintains the **highest partial pressure of oxygen ($PO_2$)** in the entire fetal venous system before it enters the right atrium [1]. **2. Analysis of Incorrect Options:** * **Superior Vena Cava (SVC):** This carries purely deoxygenated blood returning from the head, neck, and upper extremities [2]. It has one of the lowest oxygen concentrations. * **Right Ventricle:** Most of the oxygen-rich blood from the IVC is shunted directly to the left atrium via the **foramen ovale** [1], [2]. The blood that does enter the right ventricle is primarily the deoxygenated stream from the SVC, making its oxygen content lower than that of the IVC [2]. * **Aorta (ascending):** While the ascending aorta receives relatively oxygenated blood from the left ventricle to supply the brain, its oxygen concentration is slightly lower than the IVC due to the mixing that occurs in the heart chambers [2]. **NEET-PG High-Yield Pearls:** * **Highest $PO_2$ in Fetus:** Umbilical Vein (approx. 30-35 mmHg) [1]. * **Highest $PO_2$ among the given options:** IVC (specifically the segment between the ductus venosus and the heart). * **Lowest $PO_2$ in Fetus:** Umbilical Arteries (carrying waste back to the placenta) [2]. * **Crista Dividens:** The edge of the septum secundum that helps shunt the high-oxygen IVC blood toward the foramen ovale [1].

Question 219: Tertiary stem villi consist of which of the following structures?

A. A central core of cytotrophoblast covered with synctiotrophoblast.
B. A central core of extra-embryonic mesoderm covered by central cytotrophoblast and peripheral synctiotrophoblast.
C. Central maternal blood vessels surrounded by mesoderm and trophoblast.
D. Central fetal blood vessels surrounded by mesoderm and trophoblast. (Correct Answer)

Explanation: The development of chorionic villi is a high-yield topic in embryology, representing the functional evolution of the placenta [1]. The classification depends on the layers present within the villus. [2] ### 1. Why Option D is Correct **Tertiary stem villi** are characterized by the appearance of **fetal blood vessels** (angiogenesis) within the mesenchymal core [1]. By the end of the 3rd week of development, the extra-embryonic mesoderm in the villi differentiates into blood cells and small blood vessels. * **Structure:** A central core of fetal capillaries + extra-embryonic mesoderm, surrounded by an inner layer of cytotrophoblast and an outer layer of syncytiotrophoblast [3]. This establishes the embryonic circulation. ### 2. Analysis of Incorrect Options * **Option A:** Describes **Primary Villi**. These consist only of a core of cytotrophoblast covered by a layer of syncytiotrophoblast (formed in the 2nd week) [1]. * **Option B:** Describes **Secondary Villi**. These form when extra-embryonic mesoderm penetrates the core of the primary villi (early 3rd week), but before blood vessels develop [1]. * **Option C:** This is anatomically incorrect. The blood vessels within the villi are always **fetal** in origin. Maternal blood is located outside the villi, within the **intervillous spaces** [2]. ### 3. Clinical Pearls & High-Yield Facts * **Chronology:** Primary (Day 13-15) $\rightarrow$ Secondary (Day 16-18) $\rightarrow$ Tertiary (Day 19-21) [1]. * **Placental Barrier:** In early pregnancy, the barrier consists of four layers: Syncytiotrophoblast, Cytotrophoblast, Extra-embryonic mesoderm, and Fetal vascular endothelium. * **Molar Pregnancy:** Hydatidiform mole results from the cystic swelling of chorionic villi due to the absence of fetal vasculature (villi become "drops of water"). * **Hofbauer Cells:** These are specialized macrophages found within the mesoderm of the chorionic villi.

Question 220: The second pharyngeal arch is supplied by which nerve?

A. Mandibular nerve
B. Facial nerve (Correct Answer)
C. Glossopharyngeal nerve
D. Recurrent laryngeal nerve

Explanation: The pharyngeal (branchial) arches are fundamental structures in head and neck development. Each arch contains a central cartilaginous rod, muscular components, an artery (aortic arch), and a specific **cranial nerve** that supplies all structures derived from that arch. ### Why the Facial Nerve is Correct The **second pharyngeal arch** (also known as the **Hyoid arch**) is innervated by the **Facial nerve (CN VII)**. During development, the muscles of facial expression, the stapedius, stylohyoid, and the posterior belly of the digastric all migrate from the second arch mesoderm, carrying their nerve supply (CN VII) with them. ### Explanation of Incorrect Options * **A. Mandibular nerve (V3):** This is the nerve of the **first pharyngeal arch** (Mandibular arch). It supplies the muscles of mastication, tensor tympani, and tensor veli palatini. * **C. Glossopharyngeal nerve (CN IX):** This is the nerve of the **third pharyngeal arch**. It supplies the stylopharyngeus muscle. * **D. Recurrent laryngeal nerve:** This is a branch of the Vagus nerve (CN X) which supplies the **sixth pharyngeal arch** (primarily the intrinsic muscles of the larynx, except the cricothyroid). Note: The Superior laryngeal nerve supplies the **fourth arch**. ### High-Yield NEET-PG Pearls * **Skeletal Derivatives of 2nd Arch:** Stapes, Styloid process, Stylohyoid ligament, and the Lesser cornu (and upper part of the body) of the Hyoid bone. * **Mnemonic for Nerves:** "5, 7, 9, 10" (Arch 1=V, Arch 2=VII, Arch 3=IX, Arch 4/6=X). * **Clinical Correlation:** Treacher Collins Syndrome involves failure of the 1st and 2nd arch mesoderm to migrate, leading to malformation of the ears and facial bones.

Practice by Chapter

Gametogenesis and Fertilization

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Early Embryonic Development

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Placentation

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Development of Nervous System

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Development of Cardiovascular System

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Development of Gastrointestinal System

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Development of Urogenital System

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Development of Musculoskeletal System

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Development of Head and Neck

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Congenital Anomalies

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Teratology

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Molecular Mechanisms in Development

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