Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 681: What is the fate of the notochord?

A. Annulus fibrosis
B. Nucleus pulposus (Correct Answer)
C. Vertebral foramen
D. Spinous process

Explanation: ### 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).

Question 682: 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?

A. Malrotation
B. Non-rotation
C. Reverse rotation
D. Mixed rotation (Correct Answer)

Explanation: ### 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).

Question 683: Under normal conditions, where does fertilization occur in the female reproductive tract?

A. Infundibulum of the Uterine Tube
B. Ampulla of the Uterine Tube (Correct Answer)
C. Isthmus of the Uterine Tube
D. Uterine Lumen

Explanation: ### Explanation **Correct Answer: B. Ampulla of the Uterine Tube** Fertilization is the process where the male and female gametes fuse to form a zygote. Under normal physiological conditions, this occurs in the **Ampulla**, which is the widest and longest part of the uterine (Fallopian) tube [1]. The ampulla provides an optimal environment for the sperm to undergo the final stages of capacitation and for the acrosome reaction to occur upon meeting the oocyte [1]. **Analysis of Incorrect Options:** * **A. Infundibulum:** This is the funnel-shaped distal end of the tube featuring fimbriae. Its primary role is to "catch" the ovulated oocyte from the ovary and channel it into the tube [1], rather than serving as the site of fertilization. * **C. Isthmus:** This is the narrow, thick-walled segment of the tube closest to the uterus. While sperm pass through it, it is generally too narrow and distal from the ovulation site to be the primary location for fertilization. * **D. Uterine Lumen:** If an unfertilized oocyte reaches the uterus, it is typically past its viable window (12–24 hours post-ovulation). Fertilization in the uterus is abnormal; the zygote should ideally reach the uterine cavity at the **blastocyst stage**, approximately 4–5 days after fertilization [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Ectopic Pregnancy:** The **Ampulla** is also the most common site for ectopic pregnancies (approx. 70–80%). * **Timing:** Fertilization must occur within 12–24 hours after ovulation. * **Sperm Viability:** While the oocyte survives ~24 hours, sperm can survive in the female reproductive tract for up to 48–72 hours. * **Zygote Transport:** Ciliary action and muscular contractions move the zygote toward the uterus; any interference (e.g., PID) increases the risk of tubal pregnancy.

Question 684: During surgery for a benign cyst on the kidney, the surgeon notes that the patient's right kidney has two ureters and two renal pelvis. This malformation is classified as what?

A. An abnormal division of the pronephros
B. An abnormal division of the mesonephros
C. A premature division of the metanephric blastema
D. A premature division of the ureteric bud (Correct Answer)

Explanation: The development of the renal system is a frequent high-yield topic in NEET-PG. To understand this malformation, one must recall the interaction between the **ureteric bud** and the **metanephric blastema**. **1. Why the Correct Answer is Right:** The **ureteric bud** (an outgrowth of the mesonephric duct) is responsible for forming the collecting system: the ureter, renal pelvis, major/minor calyces, and collecting ducts. * If the ureteric bud divides **prematurely** (before entering the metanephric blastema), it results in a **bifid ureter** or a **double ureter** with a double renal pelvis [1]. * If two separate ureteric buds arise from the mesonephric duct, it leads to a **completely ectopic ureter**. **2. Why the Incorrect Options are Wrong:** * **Options A & B:** The **pronephros** is a vestigial structure that disappears early. The **mesonephros** functions temporarily but primarily contributes to the male reproductive system (Wolffian duct). Neither forms the definitive kidney or ureter. * **Option C:** The **metanephric blastema** (mesenchyme) forms the **excretory part** of the kidney (nephrons: Bowman’s capsule to DCT). It does not form the ureter or pelvis. An abnormal division of the blastema would more likely result in a supernumerary kidney rather than a duplicated collecting system. **3. Clinical Pearls for NEET-PG:** * **Weigert-Meyer Law:** In complete ureteral duplication, the ureter from the **upper pole** opens ectopically (inferior and medial) and is prone to **obstruction/ureterocele**, while the **lower pole** ureter opens normally but is prone to **vesicoureteral reflux (VUR)** [1]. * **Potter’s Sequence:** Caused by bilateral renal agenesis (failure of ureteric bud to induce the blastema), leading to oligohydramnios and pulmonary hypoplasia. * **Induction:** The ureteric bud and metanephric blastema exert reciprocal inductive effects on each other; if one is absent, the other fails to develop.

Question 685: Karyotyping of the fetus may be done from all of the following except:

A. Lymphocyte
B. Monocyte (Correct Answer)
C. Amniocyte
D. Fibroblast

Explanation: 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].

Question 686: Which of the following respiratory structures is derived from the neural crest?

A. Endothelial cells
B. Epithelium of primary bronchi
C. Laryngeal cartilage (Correct Answer)
D. Tracheal glands

Explanation: **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 687: The human placenta is best described as:

A. Discoidal
B. Hemochorial
C. Deciduate
D. All of the above (Correct Answer)

Explanation: The human placenta is a complex organ characterized by specific morphological and functional features [1]. The correct answer is **All of the above** because it fulfills all three descriptive criteria: 1. **Discoidal (Shape):** The term refers to the gross morphology. In humans, the chorionic villi are initially distributed over the entire chorionic sac but eventually atrophy everywhere except at the site of the *chorion frondosum*, resulting in a circular, disc-like shape [1], [2]. 2. **Hemochorial (Histology):** This describes the placental barrier. In humans, maternal blood comes into direct contact with the fetal chorion (specifically the syncytiotrophoblast) [1]. The maternal endothelial layer, connective tissue, and uterine epithelium are eroded, leaving only fetal layers to separate the two circulations. 3. **Deciduate (Shedding):** This refers to the fate of the uterine lining. At birth, a portion of the maternal endometrium (the *decidua*) is shed along with the fetal components of the placenta, often accompanied by some hemorrhage [1]. **Why individual options are not "wrong" but incomplete:** Options A, B, and C are all technically correct descriptions. In NEET-PG multiple-choice formats, when all descriptors accurately define the subject, "All of the above" is the most comprehensive and correct choice. **High-Yield Clinical Pearls for NEET-PG:** * **Placental Barrier Layers:** In a mature placenta, the barrier consists of: 1) Syncytiotrophoblast, 2) Cytotrophoblast (thins out in late pregnancy), 3) Extraembryonic mesoderm/Connective tissue, and 4) Fetal capillary endothelium [3]. * **Hormone Production:** The syncytiotrophoblast is the primary site for the secretion of hCG, hPL, Progesterone, and Estrogen [4]. * **Weight:** At term, the placenta weighs approximately 500g (1/6th of the fetal weight) [2].

Question 688: Which embryonic structure forms first?

A. Philtrum of upper lip
B. Frontonasal process (Correct Answer)
C. Maxillary process
D. Mandibular process

Explanation: The development of the face occurs primarily between the **4th and 8th weeks** of intrauterine life. The correct answer is the **Frontonasal process** because it is the primordial structure derived from the mesenchymal tissue covering the developing forebrain. It appears at the very beginning of the 4th week, slightly preceding the appearance of the pharyngeal arches. * **Frontonasal Process (Correct):** This is the first major facial prominence to appear. It gives rise to the forehead, the bridge of the nose, and the medial and lateral nasal processes. * **Mandibular Process (Option D):** This is the first component of the **1st Pharyngeal Arch** to appear (early 4th week). While it develops almost simultaneously with the frontonasal process, embryologically, the frontonasal prominence is considered the primary scaffold around which the other processes (maxillary and mandibular) organize. * **Maxillary Process (Option C):** This also arises from the 1st Pharyngeal Arch but develops **after** the mandibular process. It grows medially to form the upper cheeks and most of the upper lip. * **Philtrum of upper lip (Option A):** This is a **derivative** structure. It is formed much later (weeks 6-7) by the fusion of the two **Medial nasal processes** (which are themselves derivatives of the frontonasal process). **High-Yield NEET-PG Pearls:** 1. **1st Pharyngeal Arch (Mandibular Arch):** Gives rise to the muscles of mastication and the Nerve of the 1st arch (**Trigeminal Nerve, V2 and V3**). 2. **Cleft Lip:** Results from the failure of the **Maxillary process** to fuse with the **Medial Nasal process**. 3. **Cleft Palate:** Results from the failure of the **Palatine shelves** (from maxillary processes) to fuse with each other or the primary palate. 4. **Stomodeum:** The primitive mouth, which is separated from the foregut by the buccopharyngeal membrane.

Question 689: Which of the following tumors is associated with a defect during gastrulation?

A. Wilm's tumor
B. Sacrococcygeal teratoma (Correct Answer)
C. Astrocytoma
D. None of the above

Explanation: ### Explanation **Correct Answer: B. Sacrococcygeal teratoma** **Why it is correct:** Gastrulation is the process (occurring in the 3rd week of development) where the bilaminar germ disc is converted into a trilaminar germ disc (ectoderm, mesoderm, and endoderm) via the **primitive streak**. Normally, the primitive streak undergoes regression and disappears by the end of the fourth week. If remnants of the primitive streak persist in the sacrococcygeal region, these pluripotent cells can proliferate to form a **Sacrococcygeal teratoma** [1]. Because these cells are pluripotent, the resulting tumor typically contains tissues derived from all three germ layers (e.g., hair, muscle, and gut epithelia) [2]. **Why the other options are incorrect:** * **A. Wilm’s Tumor (Nephroblastoma):** This is a common pediatric renal tumor. It arises from the **metanephric blastema** (intermediate mesoderm) due to abnormal kidney development, not a defect in gastrulation. * **C. Astrocytoma:** This is a primary brain tumor arising from astrocytes (glial cells). While astrocytes are derived from the **neuroectoderm**, the tumor itself is an adult or pediatric neoplasm related to genetic mutations rather than a primary defect in the gastrulation process. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common:** Sacrococcygeal teratoma is the most common tumor in newborns (1 in 35,000 live births). * **Gender Predilection:** It is significantly more common in females (approx. 80% of cases). * **Remnant Origin:** Always remember: **Primitive Streak = Sacrococcygeal Teratoma**; **Notochord = Chordoma**. * **Diagnosis:** Often diagnosed via prenatal ultrasound [1]; most are benign if surgically removed promptly, but have a risk of malignant transformation if left untreated.

Question 690: Cardiac looping in a fetus occurs on which day of gestation?

A. 12-13 days of gestation
B. 16-17 days of gestation
C. 22-24 days of gestation (Correct Answer)
D. 34-35 days of gestation

Explanation: **Explanation:** The development of the heart is a high-yield topic for NEET-PG. The heart is the first functional organ to develop, beginning as a simple linear tube. **Why Option C is Correct:** Cardiac looping is the process where the primary heart tube bends to establish the basic left-right asymmetry of the heart. This process begins on **Day 22** and is typically completed by **Day 24 or 25**. During this phase, the bulbus cordis moves anteriorly, inferiorly, and to the right, while the primitive ventricle moves to the left and the atrium moves posteriorly and superiorly. This transformation is essential for the proper anatomical positioning of the cardiac chambers. **Analysis of Incorrect Options:** * **Option A (12-13 days):** At this stage, the embryo is in the late blastocyst/early gastrulation phase. The cardiogenic mesoderm has not yet formed. * **Option B (16-17 days):** This corresponds to the late gastrulation period where progenitor heart cells migrate through the primitive streak to form the primary heart field. * **Option D (34-35 days):** By this time, cardiac looping is long finished, and the heart is undergoing advanced septation (forming atrial and ventricular septa) and valve development. **High-Yield Clinical Pearls for NEET-PG:** * **Dextrocardia:** Occurs when the heart loops to the **left** instead of the right (Situs Inversus). * **Heart Beat:** The heart starts beating on **Day 21-22**, coinciding with the start of looping. * **Master Gene:** **NKX2.5** is the master gene for heart development. * **Molecular Basis:** **PITX2** is the primary gene responsible for establishing left-sidedness during looping.

Practice by Chapter

Gametogenesis and Fertilization

Practice Questions

Early Embryonic Development

Practice Questions

Placentation

Practice Questions

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

Practice Questions

Development of Musculoskeletal System

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Development of Head and Neck

Practice Questions

Congenital Anomalies

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Teratology

Practice Questions

Molecular Mechanisms in Development

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