Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 1061: When does the ossification center of the scaphoid appear?

A. 1-6 months
B. 1 to 2 years
C. 2 to 4 years
D. 4 to 6 years (Correct Answer)

Explanation: ***4 to 6 years*** - The **scaphoid** is one of the last carpal bones to ossify, with its ossification center typically appearing between **4 to 6 years of age**. - This later ossification contributes to its vulnerability to **fractures** in childhood and adolescence. *1-6 months* - The first carpal bones to ossify are the **capitate** and **hamate**, which usually appear between 1 to 6 months of age. - The scaphoid ossifies much later, making this option incorrect. *1 to 2 years* - During this period, other carpal bones like the **triquetrum** and **lunate** begin to ossify. - The scaphoid's ossification center does not typically emerge this early. *2 to 4 years* - The **trapezium** and **trapezoid** usually begin to ossify in this age range. - While closer to the scaphoid's ossification time, this period is still generally too early for the scaphoid.

Question 1062: Optic vesicle is derived from:

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

Explanation: ***Neuroectoderm*** - The **optic vesicle** is an outgrowth of the **diencephalon**, which is a part of the neural tube. - The neural tube itself develops from the **neuroectoderm**, making the optic vesicle inherently neuroectodermal in origin [2]. *Endoderm* - The **endoderm** is the innermost germ layer and forms structures like the lining of the **gastrointestinal tract**, lungs, and other visceral organs. - It does not contribute to the formation of the eye or its optic structures. *Mesoderm* - The **mesoderm** forms tissues such as **muscle**, **bone**, **connective tissue**, and the circulatory system. - While it contributes to some parts of the eye, such as the choroid and sclera, the optic vesicle specifically originates from neuroectoderm. *Surface Ectoderm* - The **surface ectoderm** gives rise to structures like the **epidermis of the skin**, hair, nails, and the **lens of the eye**. [1] - While essential for eye development, it is distinct from the neuroectoderm that forms the optic vesicle.

Question 1063: Female urethra develops from -

A. Urogenital sinus (Correct Answer)
B. Mesonephric duct
C. Ureteric bud
D. Metanephric blastema

Explanation: ***Urogenital sinus*** - The **urogenital sinus** is an endodermal structure that gives rise to the bladder, urethra, and lower vagina in females [1]. - In females, the entire urethra develops from the **pelvic part of the urogenital sinus**. *Mesonephric duct* - The **mesonephric duct** (Wolffian duct) primarily contributes to the male genital tract, forming structures like the epididymis, vas deferens, and ejaculatory ducts. - In females, the mesonephric ducts largely regress but can contribute to vestigial structures like the **Gartner's duct**. *Ureteric bud* - The **ureteric bud** is an outgrowth of the mesonephric duct that develops into the ureter, renal pelvis, calyces, and collecting ducts of the kidney. - It plays no role in the direct formation of the urethra. *Metanephric blastema* - The **metanephric blastema** is a mesenchymal tissue that interacts with the ureteric bud to form the nephrons, including the renal corpuscle and renal tubules. - It is essential for kidney development but does not contribute to the formation of the urethra.

Question 1064: Tongue muscles are derived from

A. Lateral plate mesoderm
B. Occipital myotome (Correct Answer)
C. Intermediate mesoderm
D. Cervical myotome

Explanation: Occipital myotome - The tongue muscles are innervated by the **hypoglossal nerve (CN XII)**, which is associated with the occipital somites. - During development, **occipital somites** migrate to the floor of the pharynx to form the intrinsic and extrinsic muscles of the tongue. *Lateral plate mesoderm* - The **lateral plate mesoderm** gives rise to structures like the lining of the body cavities, the serous membranes, and the smooth muscle and connective tissue of the gut wall, but not skeletal muscles of the tongue. - It also forms the **cardiac muscle** and most of the limb connective tissues. *Intermediate mesoderm* - The **intermediate mesoderm** differentiates into the urogenital system, including the kidneys, gonads, and their ducts. - It plays no direct role in the formation of skeletal muscles like those found in the tongue. *Cervical myotome* - **Cervical myotomes** contribute to the formation of muscles in the neck and diaphragm, such as the trapezius, sternocleidomastoid, and diaphragm muscles. - They do not contribute to the development of the tongue muscles, which are derived from more caudal somites.

Question 1065: Which of the following is remnant of distal umbilical artery?

A. Ligamentum Teres
B. Medial umbilical Ligament (Correct Answer)
C. Ligamentum arteriosum
D. Superior Vesical artery

Explanation: The original explanation provided does not contain sufficient information from the highly relevant references provided to support specific inline citations for every claim. For example, while the fetal circulation is discussed broadly in [2], the text provided for the other references describes fetal liver anatomy [1][2], placental umbilical cord characteristics , and general abdominal wall vascular supply without explicitly stating that the distal umbilical artery becomes the medial umbilical ligament.

Question 1066: Which of the following statements about the thymus is INCORRECT?

A. The cortical portion is mainly composed of lymphocytes
B. The medulla contains Hassall's Corpuscles
C. It undergoes atrophy from puberty onwards
D. It is derived from the fourth pharyngeal pouch (Correct Answer)

Explanation: The **thymus** is primarily derived from the **third pharyngeal pouch**, not the fourth. The fourth pharyngeal pouch contributes to the **superior parathyroid glands** and the ultimobrachial body (which gives rise to parafollicular C cells of the thyroid). *The cortical portion is mainly composed of lymphocytes* - The **thymic cortex** is densely packed with immature **T lymphocytes** (thymocytes) undergoing differentiation and selection [1], [2]. - These T cells are supported by **cortical epithelial cells** and macrophages [1]. *The medulla contains Hassall's Corpuscles* - **Hassall's corpuscles** (thymic corpuscles) are concentric layers of epithelial cells found in the **thymic medulla**. - Their exact function is debated, but they are thought to be involved in the maturation and selection of **regulatory T cells**. *It undergoes atrophy from puberty onwards* - The thymus reaches its maximum size around **puberty** and then gradually undergoes **involution** and **atrophy** throughout adulthood. - This process involves replacement of lymphoid tissue with **adipose tissue**, although it retains some residual function.

Question 1067: All of the following are derived from the neural tube EXCEPT:

A. Retina
B. Pineal gland
C. Brain
D. Dorsal root ganglia (Correct Answer)

Explanation: ***Dorsal root ganglia*** - **Dorsal root ganglia** are derived from **neural crest cells**, not the neural tube. - Neural crest cells migrate from the neural tube, forming various structures including peripheral nervous system components. *Retina* - The **retina** develops as an outgrowth or diverticulum of the **diencephalon**, which is part of the neural tube [1]. - Therefore, the retina is considered a direct derivative of the neural tube [1]. *Brain* - The entire **brain** (forebrain, midbrain, and hindbrain) develops from the cranial end of the **neural tube**. - This neural tube differentiation is crucial for the formation of all central nervous system structures. *Pineal gland* - The **pineal gland** develops as an evagination from the dorsal part of the **diencephalon**, which is a region of the neural tube. - It maintains a connection with the brain and is a central nervous system structure.

Question 1068: Kidney parenchyma is derived from -

A. Ureteric bud
B. Mesonephros
C. Metanephros (Correct Answer)
D. Paramesonephros

Explanation: Metanephros - The metanephros is the third and definitive kidney that develops embryologically, forming the functional kidney parenchyma. - The metanephric mesenchyme differentiates into the nephrons, including the glomeruli, Bowman's capsule, proximal convoluted tubule, loop of Henle, and distal convoluted tubule. - This represents the true renal parenchyma responsible for filtration and urine formation. Ureteric bud - The ureteric bud is an outgrowth of the mesonephric duct that induces the metanephric mesenchyme to differentiate. - It forms the collecting system: collecting ducts, major and minor calyces, renal pelvis, and ureters. - While essential for kidney development, it does not form the nephrons or kidney parenchyma. Mesonephros - The mesonephros is a transient embryonic kidney that functions during the first trimester before degenerating. - In males, some mesonephric tubules persist as the office-associated structures; in females, they mostly regress. - It does not contribute to the definitive kidney parenchyma. Paramesonephros - The paramesonephric (Müllerian) ducts form the female reproductive tract: fallopian tubes, uterus, and upper vagina. - They play no role in kidney development or renal parenchyma formation.

Question 1069: Part of neural tube from which corpus callosum develops

A. Basal lamina
B. Alar lamina
C. Lamina terminalis (Correct Answer)
D. Basal plate

Explanation: ***Lamina terminalis*** - The **lamina terminalis** is a thin membrane that forms the anterior wall of the third ventricle and is a key structure in the development of the **forebrain commissures**, including the **corpus callosum**. - During development, the neurons that form the **corpus callosum** and other commissures cross the midline through the **lamina terminalis** to connect the two cerebral hemispheres. *Basal lamina* - The **basal lamina** is a layer of extracellular matrix that forms part of the basement membrane and provides structural support to epithelial and endothelial cells. - It is not directly involved in the formation of the **corpus callosum** or neural tube development in this specific context. *Alar lamina* - The **alar lamina** (or alar plate) is the dorsal part of the neural tube and is primarily involved in the development of **sensory neurons** and associated structures in the CNS. - It gives rise to the **dorsal horn** of the spinal cord and sensory nuclei in the brainstem, but not the **corpus callosum**. *Basal plate* - The **basal plate** is the ventral part of the neural tube and is primarily involved in the development of **motor neurons** and associated structures in the CNS. - It gives rise to the **ventral horn** of the spinal cord and motor nuclei in the brainstem, but not the **corpus callosum** [1].

Question 1070: Facial nerve is the nerve of which of the following branchial arch?

A. First arch
B. Second arch (Correct Answer)
C. Third arch
D. Fourth arch

Explanation: ***Second arch*** - The **facial nerve (cranial nerve VII)** innervates muscles derived from the second pharyngeal (branchial) arch, such as the muscles of **facial expression**, the stapedius, stylohyoid, and posterior belly of the digastric. - This arch is also associated with the development of the **stapes**, styloid process, lesser horn of the hyoid, and upper part of the body of the hyoid bone. *First arch* - The first arch is associated with the **trigeminal nerve (cranial nerve V)**, which innervates the muscles of **mastication** and provides sensation to the face. - Structures derived from the first arch include the malleus, incus, and the mandible. *Third arch* - The third arch's nerve is the **glossopharyngeal nerve (cranial nerve IX)**, which supplies the **stylopharyngeus muscle** and provides taste and general sensation to the posterior tongue. - This arch gives rise to the greater horn of the hyoid and the lower part of the body of the hyoid. *Fourth arch* - The fourth arch is innervated by the **superior laryngeal branch of the vagus nerve (cranial nerve X)**, which supplies most of the muscles of the larynx and pharynx. - Structures formed from the fourth arch include the thyroid cartilage, cricoid cartilage, and other laryngeal cartilages.

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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