Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 1131: How many ossification centers develop at the distal end of the humerus?

A. 2
B. 3 (Correct Answer)
C. 5
D. 4

Explanation: ***3*** - The distal end of the humerus develops **three primary ossification centers**: the capitellum, trochlea, and medial epicondyle [1]. - These centers appear sequentially and their ossification pattern is important for assessing **skeletal maturity** in children using the CRITOE mnemonic [1]. - The capitellum appears at 1 year, medial epicondyle at 5 years, and trochlea at 9 years. *2* - This number is too low and only accounts for the **capitellum and medial epicondyle**, missing the trochlea. - While these are the first two to appear, there is an additional primary ossification center (trochlea) that develops later. *5* - This number is incorrect; there are only **three primary ossification centers** at the distal humerus, not five. - This may cause confusion with other joints or by counting secondary ossification centers. *4* - This number is incorrect; while the lateral epicondyle does ossify, it is not consistently counted as a **primary ossification center**. - The standard anatomical teaching recognizes **three primary centers**: capitellum, trochlea, and medial epicondyle.

Question 1132: Medulla oblongata arises from which of the following?

A. Mesencephalon
B. Myelencephalon (Correct Answer)
C. Rhombencephalon
D. None of the options

Explanation: ***Myelencephalon*** - The **myelencephalon** is the most caudal of the three primary brain vesicles and is the developmental origin of the **medulla oblongata**. - It differentiates from the **rhombencephalon** (hindbrain) and is responsible for vital autonomic functions. *Rhombencephalon* - The **rhombencephalon** is the hindbrain and is a primary brain vesicle that further divides into the **metencephalon** and **myelencephalon**. - While it is the parent structure, it does not directly give rise to the medulla oblongata as a final differentiated structure without further division. *Mesencephalon* - The **mesencephalon** is the midbrain, a primary brain vesicle that develops into structures like the **tectum** and **tegmentum** [1]. - It is located rostral to the rhombencephalon and is not involved in the development of the medulla oblongata [1]. *None of the options* - This option is incorrect because the **myelencephalon** is the direct embryonic precursor of the medulla oblongata.

Question 1133: Arch of Aorta develops from which aortic arch artery?

A. Right 3rd
B. Left 4th (Correct Answer)
C. Left 3rd
D. Right Truncus arteriosus

Explanation: ***Left 4th*** - The **arch of the aorta** develops from the **fourth left aortic arch artery**. [1] - This artery connects the **aortic sac** to the **dorsal aorta** on the left side during embryonic development. *Right Truncus arteriosus* - The **truncus arteriosus** gives rise to the **ascending aorta** and the **pulmonary artery**, not the arch of the aorta. - The term "right truncus arteriosus" is not standard in describing normal aortic arch development. *Right 3rd* - The **third aortic arch arteries** primarily contribute to the development of the **common carotid arteries** and the proximal part of the **internal carotid arteries**. - The right third aortic arch forms the proximal part of the right common carotid artery. *Left 3rd* - The **left third aortic arch artery** forms the proximal part of the **left common carotid artery** and the proximal part of the left internal carotid artery. - It does not directly form the arch of the aorta itself.

Question 1134: The cardiac jelly formed around the heart tube during early development contributes to the formation of:

A. Pericardium
B. Mesocardium
C. Myocardium
D. Endocardium (Correct Answer)

Explanation: Endocardium (Endocardial Cushions/Valves/Septa) - The **cardiac jelly** is an acellular, gelatinous matrix rich in **hyaluronic acid** that lies between the endocardium and the primordial myocardium during early heart development. - It undergoes **endothelial-to-mesenchymal transformation (EMT)** to form the **endocardial cushions** [1]. - These cushions are critical for forming: - **Atrioventricular (AV) valves** (mitral and tricuspid) [1] - **Semilunar valves** (aortic and pulmonary) [1] - **Cardiac septa** (portions of atrial, ventricular, and AV septa) [1] - While cardiac jelly doesn't form the endocardial lining itself (which is already present as endothelium), it forms the endocardial cushions that are essential endocardial derivatives. *Pericardium* - The **pericardium** develops from the **pleuropericardial folds** and **somatic and splanchnic mesoderm**, forming the fibrous and serous outer coverings of the heart. - It is completely distinct from cardiac jelly, which is an intra-cardiac structure. *Mesocardium* - The **dorsal mesocardium** is a transient mesentery that temporarily connects the developing heart tube to the dorsal wall of the pericardial cavity. - It rapidly degenerates by **day 22-23** to form the **transverse pericardial sinus**. - It does not contribute to cardiac jelly or any heart wall structures. *Myocardium* - The **myocardium** differentiates directly from the **splanchnic mesoderm** surrounding the endocardial tube. - It forms the muscular contractile layer of the heart wall. - Cardiac jelly lies between the endocardium and myocardium but does not form myocardial tissue.

Question 1135: Collecting part of kidney develops from ?

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

Explanation: ***Ureteric bud*** - The **ureteric bud** (also known as the metanephric diverticulum) is an outgrowth of the **mesonephric duct** that develops into the collecting system of the kidney. - It gives rise to the **ureter**, **renal pelvis**, major and minor calyces, and all collecting ducts. *Pronephros* - **Pronephros** is the earliest, most rudimentary, and transient excretory structure that appears in human embryos. - It is non-functional in humans and **degenerates completely** by the fourth week of gestation. *Mesonephros* - The **mesonephros** develops after the pronephros and functions as a temporary kidney during the early fetal period (weeks 4-8). - Its tubules primarily contribute to the **male reproductive system** (e.g., epididymis, ductus deferens) and **degenerate** in females. *Metanephros* - The **metanephros** is the definitive kidney in mammals and gives rise to the **nephrons** (glomeruli, Bowman's capsule, proximal and distal convoluted tubules, loop of Henle). - While it's crucial for kidney development, the **collecting part** specifically originates from the ureteric bud, which interacts with the metanephric mesenchyme.

Question 1136: Sinus venosus receives blood from all EXCEPT:

A. Vitelline vein
B. Umbilical vein
C. Common cardinal vein
D. Subcardinal vein (Correct Answer)

Explanation: Sinus venosus receives blood from all EXCEPT: ***Subcardinal vein*** - The **subcardinal vein** is primarily involved in draining the developing **kidneys** and gonads during embryonic development. - While it contributes to the formation of the **inferior vena cava**, it does not directly empty into the sinus venosus. - The subcardinal veins are part of a different venous drainage system that develops independently from the sinus venosus tributaries. *Vitelline vein* - The **vitelline veins** drain blood from the **yolk sac**, which is the primary site of early hematopoiesis. - These veins directly empty into the **sinus venosus** in the early embryo. - They eventually give rise to the **hepatic portal system** and hepatic sinusoids. *Umbilical vein* - The **umbilical vein** carries **oxygenated and nutrient-rich blood** from the placenta to the fetus [1]. - In the early embryo, the umbilical veins drain directly into the **sinus venosus**. - Later in development, the left umbilical vein bypasses the liver via the **ductus venosus** to enter the inferior vena cava [1], [2]. *Common cardinal vein* - The **common cardinal veins** collect blood from the entire embryo, draining both the anterior (from the cephalic region) and posterior (from the trunk and lower limbs) parts. - These veins represent the main drainage system of the developing embryo and directly empty into the sinus venosus. - They are the primary tributaries of the sinus venosus during early cardiac development.

Question 1137: Double inferior vena cava is formed due to?

A. Persistence of both supracardinal and subcardinal veins
B. Persistence of sacrocardinal veins
C. Persistence of subcardinal veins
D. Persistence of supracardinal veins (Correct Answer)

Explanation: ***Persistence of supracardinal veins*** - A double inferior vena cava (IVC) results from the **persistence of the left supracardinal vein**, which normally regresses. - This malformation causes the IVC to be duplicated below the level of the renal veins, creating two parallel venous channels ascending to join the normal IVC or renal veins. *Persistence of sacrocardinal veins* - The sacrocardinal veins are involved in the development of the **iliac veins** and the distal part of the IVC, but their independent persistence does not lead to a double IVC. - Abnormalities in sacrocardinal vein development are more commonly associated with conditions like **agenesis of the infrarenal IVC**. *Persistence of subcardinal veins* - The subcardinal veins mainly contribute to the formation of the **renal segment** of the IVC and the gonadal veins. - Their persistence or malformation can lead to a **retrocaval ureter** or other venous anomalies, but not a double IVC. *Persistence of both supracardinal and subcardinal veins* - While both supracardinal and subcardinal veins are crucial for IVC development, their **simultaneous persistence** in a way that creates a double IVC is not the direct mechanism [1]. - A double IVC is specifically attributed to the **persistence of the left supracardinal vein**, with the right supracardinal vein forming the normal right IVC [1].

Question 1138: At which level do the somites initially form?

A. Lumbar level
B. Sacral level
C. Cervical level (Correct Answer)
D. Thoracic level

Explanation: Cervical level - Somites, which are segmented blocks of paraxial mesoderm, initially appear in the **occipital/cranial cervical region** of the developing embryo around day 20 of development. - The first somite pair forms at the **occipital level**, and subsequent somites develop in a **cranio-caudal sequence**. - Development proceeds both cranially (forming occipital somites) and caudally (forming cervical, thoracic, lumbar, and sacral somites) from this initial formation. - By the end of the 5th week, approximately **42-44 somite pairs** are present. *Thoracic level* - Thoracic somites form subsequent to the initial occipital/cervical somites, as the segmentation process extends caudally. - The formation of somites is a sequential process along the **cranio-caudal axis**. *Lumbar level* - Lumbar somites develop later in the embryological timeline, after the cervical and thoracic regions have undergone somite formation. - The **caudal regions** receive somites progressively as development continues. *Sacral level* - Sacral somites are among the last to form, representing the caudal extent of somite development. - Their formation follows the cranio-caudal progression of somite appearance.

Question 1139: Which of the following is not a neural plate inducer?

A. FGF upregulation
B. Prechordal mesoderm
C. High BMP (Correct Answer)
D. Notochord appearance

Explanation: High BMP - **Bone Morphogenetic Proteins (BMPs)** are primarily involved in promoting epidermal differentiation in the ectoderm, and actively **inhibiting neural differentiation**. - Therefore, high levels of BMP would **prevent neural plate formation**, rather than induce it. *FGF upregulation* - **Fibroblast Growth Factors (FGFs)** are crucial in the early development of the nervous system. - They play a key role in **inducing neural plate formation** and maintaining its identity. *Prechordal mesoderm* - The **prechordal mesoderm**, located anterior to the notochord, is an important signalling center during early embryonic development. - It contributes to the **induction of the forebrain** and plays a role in patterning the anterior neural plate. *Notochord appearance* - The **notochord**, a transient rod-like structure, is a primary inducer of the neural plate. - It secretes factors like **Sonic Hedgehog (Shh)** which induce the overlying ectoderm to differentiate into neuroectoderm, forming the neural plate.

Question 1140: What is a characteristic feature observed in a fetus at approximately 12 weeks of gestation?

A. Anus is seen as dark spot
B. Meconium is found in duodenum
C. Nails are visible
D. Limbs well formed (Correct Answer)

Explanation: ***Limbs well formed*** - By **12 weeks gestation**, the limbs are well formed, with fingers and toes identifiable, although movements are often still subtle and not yet felt by the mother. - This stage marks significant progression in **skeletal and muscular development**, allowing for more defined body structures [1]. *Nails are visible* - **Nail development** typically begins around **12-13 weeks**, but they are usually not clearly or distinctly visible until much later in gestation, often around **20 weeks or more**. - At 12 weeks, the focus is on the basic formation of digits rather than the intricate details of nail plates. *Anus is seen as dark spot* - The formation of the **anus and anal canal** occurs much earlier in embryonic development, around weeks 7-8, following the separation of the cloaca. - While present, it's not a characteristic feature that uniquely distinguishes the 12-week stage; its visibility as a "dark spot" is not a primary developmental landmark at this specific point. *Meconium is found in duodenum* - **Meconium formation** involves the accumulation of swallowed amniotic fluid, shed cells, and gastrointestinal secretions, which typically starts around **12-16 weeks** [2] but primarily collects in the large intestine. - Although the digestive system is developing, the primary accumulation of meconium and its typical presence in the duodenum as a notable feature is not characteristic of the 12-week mark.

Practice by Chapter

Gametogenesis and Fertilization

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Early Embryonic Development

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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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Congenital Anomalies

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Teratology

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Molecular Mechanisms in Development

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