Embryology and Development Practice Questions

Q: The primordial germ cells that eventually form the oogonia and spermatogonia originate in which of the following?

Endodermal lining of the yolk sac. ### Explanation **1. Why the Correct Answer is Right:** Primordial germ cells (PGCs) are the precursors of gametes (oogonia and spermatogonia). They do not originate within the developing gonads themselves. Instead, they first appear during the **4th week of development** [2] in the **epiblast** and subsequently migrate to the **endodermal lining of the yolk sac** (specifically near the allantois). From here, they migrate via amoeboid movement through the dorsal mesentery to reach the primitive gonads by the 5th or 6th week [1]. **2. Analysis of Incorrect Options:** * **Option A (Dorsal mesentery of the hindgut):** This is the **pathway** or "highway" through which the PGCs migrate to reach the gonadal ridge, but it is not their site of origin. * **Option B (Gonadal ridge):** This is the **destination**. The gonadal ridge is formed by the proliferation of coelomic epithelium and underlying mesenchyme. If PGCs fail to reach this ridge, the gonads do not develop. * **Option D (Primary sex cords):** These are finger-like projections of the coelomic epithelium that grow into the mesenchyme of the gonadal ridge. They surround the PGCs but do not give rise to them [1]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Extragonadal Teratomas:** If PGCs stray from their migratory path and lodge in extragonadal sites (like the mediastinum or sacrococcygeal region), they may give rise to teratomas. * **Timeline:** PGCs originate in the **2nd week** (epiblast), move to the **yolk sac** in the **4th week**, and reach the **gonadal ridge** by the **6th week** [1]. * **Inductive Influence:** The PGCs have an inductive effect on the development of the gonad into an ovary or testis; however, the genetic sex is determined at fertilization by the SRY gene on the Y chromosome.

Q: A 3-year-old boy presents with restlessness, abdominal pain, and fever. An MRI reveals a double ureter. Which of the following embryonic structures is most likely to have failed to develop normally?

Ureteric bud. ### Explanation **Correct Option: C. Ureteric bud** The urinary system develops from the intermediate mesoderm. The **ureteric bud** is an outgrowth from the caudal end of the **Mesonephric (Wolffian) duct**. It is responsible for forming the **conducting part** of the kidney, which includes the ureter, renal pelvis, major and minor calyces, and collecting tubules. A **double ureter (duplex collecting system)** occurs due to the premature branching or "splitting" of a single ureteric bud before it enters the metanephric blastema, or the development of two separate ureteric buds from the mesonephric duct. This is the most common renal congenital anomaly [1]. **Why other options are incorrect:** * **A. Mesonephric (Wolffian) duct:** While the ureteric bud arises from this duct, the duct itself primarily forms the male reproductive structures (Epididymis, Vas deferens, Seminal vesicles). It does not directly form the ureter. * **B. Paramesonephric (Mullerian) duct:** This structure forms the female reproductive tract (Uterine tubes, Uterus, Upper vagina). It has no role in the development of the urinary collecting system. * **D. Metanephros (Metanephric Blastema):** This forms the **excretory part** of the kidney, including the Bowman’s capsule, proximal convoluted tubule, Loop of Henle, and distal convoluted tubule. Failure here leads to renal agenesis or dysplasia, not a double ureter. **High-Yield Clinical Pearls for NEET-PG:** * **Weigert-Meyer Law:** In a complete double ureter, the ureter from the **upper pole** opens ectopically (inferior and medial) to the ureter from the lower pole [1]. The upper pole ureter often ends in a **ureterocele**, while the lower pole ureter is prone to **vesicoureteral reflux (VUR)** [1]. * **Induction:** The ureteric bud must meet the metanephric blastema to induce kidney formation. If they fail to meet, **renal agenesis** occurs.

Q: During ovulation, at what specific stage of meiosis does the secondary oocyte reside?

Metaphase II. The correct answer is **Metaphase II**. This question tests the understanding of the specific arrest points in oogenesis, a high-yield topic for NEET-PG. **1. Why Metaphase II is correct:** Oogenesis is a discontinuous process. Primary oocytes begin meiosis I during fetal life but are arrested in Prophase I [2]. At puberty, each month, a few follicles resume meiosis. The primary oocyte completes Meiosis I just before ovulation, forming a secondary oocyte and the first polar body [1]. The secondary oocyte then enters Meiosis II but **arrests for the second time in Metaphase II**. It is released from the Graafian follicle in this arrested state during ovulation. Meiosis II is only completed if fertilization occurs (triggered by the sperm's entry). **2. Why other options are incorrect:** * **Prophase I:** This is the first arrest point (specifically the **Diplotene stage**). Oocytes remain in this stage from fetal life until puberty [2]. * **Metaphase I:** This is a transient stage during the completion of the first meiotic division; the oocyte does not arrest here. * **Prophase II:** This stage occurs briefly after the completion of Meiosis I before the oocyte arrests in Metaphase II. **3. Clinical Pearls & High-Yield Facts:** * **Two Arrests:** 1. **1st Arrest:** Prophase I (Diplotene stage) — mediated by Oocyte Maturation Inhibitor (OMI) [2]. 2. **2nd Arrest:** Metaphase II — mediated by **Cytostatic Factor (CSF)**. * **Fertilization Trigger:** Completion of Meiosis II is triggered by a rise in intracellular calcium upon sperm entry, which degrades the APC/C inhibitor. * **Chromosomal Status:** At ovulation, the secondary oocyte is **haploid (n)** but contains **double the DNA (2c)** because sister chromatids have not yet separated.

Q: What is the remnant of the ductus venosus?

Ligamentum venosum. ### Explanation The correct answer is **Ligamentum venosum**. **1. Understanding the Correct Answer:** During fetal life, the **ductus venosus** is a critical vascular shunt that allows oxygenated blood from the umbilical vein to bypass the hepatic capillary bed and flow directly into the Inferior Vena Cava (IVC) [1]. Upon birth, the cessation of placental blood flow and the subsequent decrease in pressure lead to the functional closure of this shunt. Anatomically, it fibroses to become the **ligamentum venosum**, which is found in the fissure for ligamentum venosum on the posterior (visceral) surface of the liver, separating the left lobe from the caudate lobe [3]. **2. Analysis of Incorrect Options:** * **A. Ligamentum teres:** This is the remnant of the **left umbilical vein** [1]. It runs in the free margin of the falciform ligament and extends from the umbilicus to the liver. * **C. Ligamentum arteriosum:** This is the remnant of the **ductus arteriosus**, which shunts blood from the pulmonary artery to the aorta in the fetus to bypass the non-functional lungs. * **D. Falciform ligament:** This is a derivative of the **ventral mesogastrium**, not a vascular remnant [2]. It attaches the liver to the anterior abdominal wall. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Remnants:** * **D**uctus **V**enosus $\rightarrow$ Ligamentum **V**enosum (Both have 'V'). * **U**mbilical **V**ein $\rightarrow$ Ligamentum **T**eres (UV-T). * **Clinical Correlation:** In cases of portal hypertension, the ligamentum teres may "recanalize," leading to the clinical sign known as **Caput Medusae**. * **Fetal Circulation:** The ductus venosus carries the highest oxygen saturation (approx. 80%) in the fetal circulatory system [1].

Q: What is the fate of the notochord?

Nucleus pulposus. ### Explanation **Correct Option: B. Nucleus pulposus** The **notochord** is a primitive, flexible rod-like structure that defines the longitudinal axis of the embryo [1]. During the development of the vertebral column, the notochord is largely replaced by the vertebral bodies. However, it persists in the center of the intervertebral discs, where it differentiates into the **nucleus pulposus**—the gelatinous core that provides shock absorption. **Analysis of Incorrect Options:** * **A. Annulus fibrosis:** This is the tough, fibrous outer ring of the intervertebral disc. It is derived from the **mesenchyme of the sclerotome**, not the notochord. * **C & D. Vertebral foramen and Spinous process:** These are bony components of the vertebral arch. The entire vertebra (body, arch, and processes) develops from the **sclerotome** part of the somites through the process of endochondral ossification [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Chordoma:** This is a rare, slow-growing malignant tumor that arises from **remnants of the notochord**. It most commonly occurs at the base of the skull (clivus) or the sacrococcygeal region. * **Inductive Role:** The primary function of the notochord in early development is to act as the "primary organizer," inducing the overlying ectoderm to thicken and form the **neural plate** (neurulation). * **Remnants:** Apart from the nucleus pulposus, notochordal remnants may also contribute to the **apical ligament** of the dens (axis vertebra).

Q: The caecum is found to be placed below the stomach and in the midline. Which of the following abnormalities must have taken place during the rotation of the gut?

Mixed rotation. ### Explanation **1. Why Mixed Rotation is Correct:** In normal development, the midgut undergoes a **270° counter-clockwise rotation** around the superior mesenteric artery (SMA). **Mixed rotation** occurs when the initial 90° rotation occurs normally, but the subsequent 180° rotation fails or occurs abnormally. Specifically, the cephalic limb (small intestine) rotates, but the caudal limb (large intestine) fails to complete its rotation [1]. This results in the **caecum being fixed in the midline, just below the stomach**, often attached to the posterior abdominal wall by abnormal peritoneal bands (**Ladd’s bands**). These bands can cross the duodenum, leading to high intestinal obstruction. **2. Analysis of Incorrect Options:** * **Non-rotation (B):** The midgut fails to rotate after the first 90° [2]. This results in a "left-sided colon" where the small intestine lies on the right and the entire large intestine lies on the left side of the abdomen. * **Reverse rotation (C):** The midgut rotates **clockwise** instead of counter-clockwise. This leads to the **transverse colon being placed behind the SMA** and the duodenum being in front of it, which can cause colonic obstruction. * **Malrotation (A):** This is a general umbrella term for any deviation from normal rotation. While technically correct in a broad sense, "Mixed rotation" is the specific anatomical description for the caecum's sub-gastric, midline position. **3. High-Yield Clinical Pearls for NEET-PG:** * **Ladd’s Bands:** Fibrous stalks associated with malrotation that can cause duodenal compression. * **Volvulus:** The most dreaded complication of malrotation due to a narrow mesenteric base. * **Gold Standard Investigation:** Upper GI Contrast Study (shows "corkscrew" appearance of the duodenum). * **Surgical Procedure:** **Ladd’s Procedure** (widening the mesentery, dividing bands, and placing the small bowel on the right and large bowel on the left).

Q: Karyotyping of the fetus may be done from all of the following except:

Monocyte. Karyotyping requires cells that are actively undergoing **mitosis** (specifically arrested in metaphase) or cells that can be stimulated to divide in a culture medium [3]. **Why Monocytes are the correct answer (Except):** Monocytes are **terminally differentiated** cells in the peripheral blood. Unlike lymphocytes, they do not readily undergo mitosis in standard culture media used for karyotyping. While they are nucleated, they are not the preferred source for chromosomal analysis because they cannot be easily stimulated to divide into a sufficient number of metaphase spreads required for a diagnostic karyotype. **Analysis of other options:** * **Lymphocytes (Option A):** These are the most common source for postnatal karyotyping. Though they are mature cells, they can be stimulated to enter mitosis using mitogens like **Phytohemagglutinin (PHA)**. * **Amniocytes (Option C):** These are fetal cells shed into the amniotic fluid. They are routinely cultured for prenatal diagnosis (Amniocentesis) as they are actively dividing [2, 4]. * **Fibroblasts (Option D):** Obtained via skin biopsy, fibroblasts are robust dividers in culture. They are often used when a mosaicism is suspected or when a permanent cell line is needed. **NEET-PG High-Yield Pearls:** * **Colchicine:** Used in karyotyping to arrest cells in **metaphase** by inhibiting spindle formation [3]. * **Best source for rapid prenatal karyotyping:** Chorionic Villus Sampling (CVS) can provide results faster than amniocentesis [1]. * **Barr Body:** Represents the inactivated X-chromosome (Lyonization), seen in females. The number of Barr bodies = (Total X chromosomes - 1). * **Tissues used for Karyotyping:** Peripheral blood (Lymphocytes), Bone marrow (for leukemias), Skin (Fibroblasts), and Products of Conception (Amniocytes/Chorionic villi) [2, 4].

Q: Which of the following respiratory structures is derived from the neural crest?

Laryngeal cartilage. **Explanation:** The respiratory system develops from multiple germ layers, but the **laryngeal cartilages** (thyroid, cricoid, and arytenoid) are unique because they are derived from the **neural crest cells** within the mesenchyme of the 4th and 6th pharyngeal arches. While most of the skeletal framework of the body comes from mesoderm, the bones and cartilages of the head and neck are primarily neural crest derivatives. **Analysis of Options:** * **A. Endothelial cells:** These form the lining of the pulmonary capillaries and are derived from the **splanchnic mesoderm**. * **B. Epithelium of primary bronchi:** The entire internal lining (epithelium) of the larynx, trachea, bronchi, and the mucosal glands originates from the **endoderm** (specifically the laryngotracheal diverticulum). * **D. Tracheal glands:** Since these are invaginations of the surface epithelium, they are also **endodermal** in origin. **High-Yield Clinical Pearls for NEET-PG:** * **Endoderm:** Gives rise to the epithelial lining and glands of the entire respiratory tract. * **Splanchnic Mesoderm:** Gives rise to the smooth muscle, connective tissue, and visceral pleura. * **Neural Crest:** Specifically forms the laryngeal cartilages. *Note: The epiglottis is an exception; it develops from the hypobranchial eminence (mesoderm).* * **Key Landmark:** The respiratory system begins as a median outgrowth called the **respiratory diverticulum** (lung bud) appearing in the ventral wall of the foregut.

Question 1

The renal arteries are branches of which of the following arteries?

Accepted Answer

Internal pudendal artery

Answer

External iliac artery

Answer

Common iliac artery

Answer

Abdominal aorta

Question 2

The primordial germ cells that eventually form the oogonia and spermatogonia originate in which of the following?

Accepted Answer

Endodermal lining of the yolk sac

Answer

Dorsal mesentery of the hindgut

Answer

Gonadal ridge

Answer

Primary sex cords of the developing gonad

Question 3

Continued production of estrogen and progesterone from the corpus luteum of the ovary is essential during the implantation process. The corpus luteum of the ovary (now known as the corpus luteum of pregnancy) is maintained by the secretion of human chorionic gonadotropin from which source?

Accepted Answer

The trophoblast cells

Answer

The embryoblast cells

Answer

The endometrial glands

Answer

The hypoblast cells

Question 4

A 3-year-old boy presents with restlessness, abdominal pain, and fever. An MRI reveals a double ureter. Which of the following embryonic structures is most likely to have failed to develop normally?

Accepted Answer

Ureteric bud

Answer

Mesonephric (Wolffian) duct

Answer

Paramesonephric (Mullerian) duct

Answer

Metanephros

Question 5

During ovulation, at what specific stage of meiosis does the secondary oocyte reside?

Accepted Answer

Metaphase II

Answer

Prophase I

Answer

Prophase II

Answer

Metaphase I

Question 6

What is the remnant of the ductus venosus?

Accepted Answer

Ligamentum venosum

Answer

Ligamentum teres

Answer

Ligamentum arteriosum

Answer

Falciform ligament

Question 7

What is the fate of the notochord?

Accepted Answer

Nucleus pulposus

Answer

Annulus fibrosis

Answer

Vertebral foramen

Answer

Spinous process

Question 8

The caecum is found to be placed below the stomach and in the midline. Which of the following abnormalities must have taken place during the rotation of the gut?

Accepted Answer

Mixed rotation

Answer

Malrotation

Answer

Non-rotation

Answer

Reverse rotation

Question 9

Karyotyping of the fetus may be done from all of the following except:

Accepted Answer

Monocyte

Answer

Lymphocyte

Answer

Amniocyte

Answer

Fibroblast

Question 10

Which of the following respiratory structures is derived from the neural crest?

Accepted Answer

Laryngeal cartilage

Answer

Endothelial cells

Answer

Epithelium of primary bronchi

Answer

Tracheal glands

Embryology and Development — MCQs

Embryology and Development — MCQs

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