Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 491: Which structure is not found between the cytotrophoblast and the maternal blood in the developing placenta?

A. Decidua parietalis (Correct Answer)
B. Syncytiotrophoblast
C. Intervillous space
D. Basement membrane

Explanation: ### Explanation The question tests the understanding of the **placental barrier** and the layers of the **decidua**. **Why Decidua Parietalis is the Correct Answer:** The placenta develops specifically from the **Decidua basalis** (maternal component) and the **Chorion frondosum** (fetal component) [1]. The **Decidua parietalis** is the portion of the uterine lining that lines the rest of the uterine cavity away from the implantation site [2]. Since it does not participate in the formation of the placenta or the interface between fetal cells and maternal blood, it is not found between the cytotrophoblast and maternal blood. **Analysis of Incorrect Options:** * **Syncytiotrophoblast:** This is the outermost fetal layer that directly erodes maternal sinusoids [1]. It is the primary barrier in contact with maternal blood [4]. * **Intervillous space:** This is the space formed by the erosion of maternal vessels where maternal blood actually flows [1]. It sits directly "outside" the trophoblastic layers [3]. * **Basement membrane:** In the early placental barrier, a basement membrane exists beneath the syncytiotrophoblast, separating it from the underlying cytotrophoblast and fetal capillary endothelium [3]. **High-Yield NEET-PG Pearls:** 1. **The Placental Barrier (Early):** Consists of 4 layers: Syncytiotrophoblast, Cytotrophoblast, Extraembryonic mesoderm (connective tissue), and Fetal capillary endothelium [3]. 2. **The Placental Barrier (Late/Term):** Becomes thinner to facilitate exchange. The cytotrophoblast and mesoderm largely disappear, leaving mainly the syncytiotrophoblast and fetal endothelium. 3. **Decidua Types:** * *Basalis:* At the implantation site (forms maternal placenta) [2]. * *Capsularis:* Encloses the embryo [2]. * *Parietalis:* Lines the remainder of the uterus [2]. 4. **Nitabuch’s Layer:** A fibrinoid degeneration zone between the trophoblast and decidua basalis that prevents overly deep implantation [3].

Question 492: All of the following develop from the endodermal cloaca except:

A. Rectum
B. Anal canal
C. Sigmoid (Correct Answer)
D. Primitive urogenital sinus

Explanation: ### Explanation The **cloaca** is the terminal dilated part of the hindgut, lined by endoderm. During the 4th to 7th weeks of development, it is divided by the **urorectal septum** into a dorsal **primitive anorectal canal** and a ventral **primitive urogenital sinus** [1]. **1. Why Sigmoid is the Correct Answer:** The **sigmoid colon** develops from the **hindgut** proper, not the cloaca [2]. The hindgut gives rise to the distal third of the transverse colon, descending colon, and sigmoid colon [3]. While the cloaca is a derivative of the hindgut, it specifically forms the terminal structures (rectum and upper anal canal) rather than the proximal segments like the sigmoid. **2. Analysis of Incorrect Options:** * **Rectum:** This develops from the dorsal part of the cloaca (primitive anorectal canal) after the urorectal septum divides it [1]. * **Anal Canal:** Only the **upper part** (above the pectinate line) develops from the endodermal cloaca. The lower part develops from the ectodermal proctodeum. * **Primitive Urogenital Sinus:** This is the ventral division of the cloaca [1]. It further differentiates into the urinary bladder, urethra, and (in males) the prostatic and membranous urethra or (in females) the vestibule of the vagina [4]. **3. NEET-PG High-Yield Pearls:** * **The Pectinate Line:** This is the site of the former **cloacal membrane**. It marks the transition of epithelium (columnar to stratified squamous), nerve supply (autonomic to somatic), and lymphatic drainage. * **Urorectal Septum:** Failure of this septum to fuse with the cloacal membrane leads to **rectovaginal or rectourethral fistulas**. * **Imperforate Anus:** Occurs when the anal membrane fails to perforate.

Question 493: Which part of the sperm contains mitochondria?

A. Golgi apparatus
B. Mitochondria (Correct Answer)
C. Lysosome
D. Ribosome

Explanation: The mature human sperm (spermatozoon) is divided into a head, neck, middle piece, principal piece, and end piece [1]. The **middle piece (midpiece)** specifically contains the **mitochondria**, which are arranged in a tight spiral (the mitochondrial sheath or *nebenkern*). These mitochondria are essential for providing the ATP (energy) required for flagellar movement and sperm motility. **Analysis of Options:** * **B. Mitochondria (Correct):** As mentioned, these are localized in the middle piece. They utilize fructose from seminal fluid to generate energy for the sperm's journey through the female reproductive tract. * **A. Golgi apparatus:** In the developing spermatid, the Golgi apparatus gives rise to the **Acrosome** (the cap-like structure on the head containing enzymes for fertilization) [1]. It is not the site of energy production. * **C. Lysosome:** While the acrosome is often considered a specialized lysosome (containing hydrolytic enzymes like acrosin and hyaluronidase), "lysosome" is not the anatomical part containing mitochondria. * **D. Ribosome:** Mature sperm are specialized for delivery and have minimal cytoplasm; they lack functional ribosomes as protein synthesis is largely halted after spermiogenesis. **High-Yield NEET-PG Pearls:** * **Mitochondrial Inheritance:** All mitochondria in the zygote are **maternally derived**. The paternal mitochondria in the sperm's midpiece are usually tagged with ubiquitin and degraded upon entering the oocyte [3]. * **Axoneme:** The core of the sperm tail (flagellum) consists of a **9+2 arrangement** of microtubules. * **Kartagener Syndrome:** A clinical condition involving dynein arm defects leading to immotile cilia and sperm, resulting in male infertility [2].

Question 494: The appendix of the testis is a remnant of which embryonic structure?

A. Mesonephric duct
B. Paramesonephric duct (Correct Answer)
C. Paramesonephric tubule
D. Mesonephric tubule

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The **Appendix of the testis** (Hydatid of Morgagni) is a small, sessile vestigial structure located at the upper pole of the testis. In males, the **Paramesonephric duct (Müllerian duct)** normally regresses due to the secretion of Anti-Müllerian Hormone (AMH) by Sertoli cells [1]. However, its cranial-most tip persists as the appendix of the testis. In females, this same duct develops into the fallopian tubes, uterus, and upper part of the vagina. **2. Analysis of Incorrect Options:** * **A. Mesonephric duct (Wolffian duct):** In males, this duct gives rise to the epididymis, vas deferens, and seminal vesicles [1]. Its remnant in the male is the **Appendix of the epididymis**. * **C. Paramesonephric tubule:** This is a distractor term; the paramesonephric system consists of ducts, not specific "tubules" that form the appendix. * **D. Mesonephric tubule:** These tubules form the efferent ductules (vasa efferentia) of the testis. Remnants of these tubules include the **Paradidymis** (Organ of Giraldés). **3. NEET-PG High-Yield Clinical Pearls:** * **Torsion of the Appendix Testis:** This is a common cause of acute scrotum in prepubertal boys. It presents with a pathognomonic **"Blue Dot Sign"** (a blue-colored nodule visible through the scrotal skin). * **Prostatic Utricle:** This is the other significant male remnant of the Paramesonephric duct (representing the primitive uterus/vagina). * **Gartner’s Duct:** The female remnant of the Mesonephric duct (found in the broad ligament or vaginal wall). * **Epoophoron/Paroophoron:** Female remnants of the Mesonephric tubules.

Question 495: Cantrell pentalogy is associated with which of the following?

A. Omphalocele (Correct Answer)
B. Ileal atresia
C. Gastroschisis
D. None of the above

Explanation: **Explanation:** **Cantrell Pentalogy** (also known as Pentalogy of Cantrell) is a rare congenital syndrome characterized by a specific constellation of five midline developmental defects. These defects result from a failure of the lateral mesodermal folds to migrate and fuse in the midline during the early embryonic period (around 14–18 days after conception). The five defining features are: 1. **Omphalocele:** A midline abdominal wall defect at the level of the umbilicus where viscera are herniated and covered by a peritoneal sac. 2. **Ectopia Cordis:** Displacement of the heart outside the thoracic cavity. 3. **Diaphragmatic Defect:** Specifically, a defect in the anterior (sternal) portion of the diaphragm. 4. **Sternal Cleft:** Bifid or absent lower sternum. 5. **Pericardial Defect:** A communication between the pericardial and peritoneal cavities (diaphragmatic pericardium). **Why other options are incorrect:** * **Gastroschisis:** Unlike omphalocele, gastroschisis is a para-umbilical defect (usually to the right) where the bowel is exposed without a covering sac [1]. It is not part of the Cantrell Pentalogy. * **Ileal Atresia:** This is a vascular accident or canalization failure of the midgut, unrelated to the midline fusion defects seen in this syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Association:** Often associated with chromosomal abnormalities like **Trisomy 18 and 13**. * **Imaging:** Prenatal diagnosis is possible via ultrasound by identifying ectopia cordis and omphalocele together. * **Key Differentiator:** If a question mentions "heart beating outside the chest" + "umbilical swelling," always think of Cantrell Pentalogy.

Question 496: Exposure of a female fetus to androgens in early embryogenesis may arrest the differentiation of which structure?

A. Mullerian ducts
B. Ovary
C. Urogenital sinus (Correct Answer)
D. Mesonephric ducts

Explanation: **Explanation:** The differentiation of the female external genitalia and the lower portion of the vagina depends on the **absence of androgens**. In a female fetus, the **Urogenital Sinus (UGS)** is programmed to develop into the lower 2/3rd of the vagina, the urethra, and the vestibule. If exposed to high levels of androgens (e.g., in Congenital Adrenal Hyperplasia) during the critical period of 8–12 weeks, the UGS fails to differentiate into separate vaginal and urethral openings [1]. Instead, it undergoes "masculinization," leading to clitoromegaly and fusion of the labioscrotal folds, effectively arresting normal female development [2]. **Why other options are incorrect:** * **Mullerian ducts:** Their development into the uterus, fallopian tubes, and upper 1/3rd of the vagina is independent of androgens [2]. It depends solely on the **absence of Anti-Mullerian Hormone (AMH)**. * **Ovary:** Gonadal differentiation (ovary vs. testis) is determined by the presence or absence of the **SRY gene** on the Y chromosome, not by circulating androgens. * **Mesonephric (Wolffian) ducts:** These require testosterone to persist and develop into male internal structures (epididymis, vas deferens) [2]. In a normal female, they regress due to a lack of testosterone; androgen exposure would actually *promote* their growth rather than arrest it. **NEET-PG High-Yield Pearls:** * **Internal Genitalia:** Determined by AMH (Paramesonephric/Mullerian duct regression). * **External Genitalia:** Determined by Androgens/DHT (Urogenital sinus and genital tubercle differentiation) [2]. * **Clinical Correlation:** Female pseudohermaphroditism (46, XX DSD) is most commonly caused by **Congenital Adrenal Hyperplasia (21-hydroxylase deficiency)**, leading to androgen-induced virilization of the urogenital sinus [1].

Question 497: All of the following statements are true regarding thyroid development except?

A. Endodermal in nature
B. Foramen caecum forms thyroglossal duct
C. Parafollicular C cells are formed from 2nd pouch (Correct Answer)
D. Parafollicular C cells are derived from neural crest cells

Explanation: ### Explanation **1. Why Option C is the Correct Answer (The Exception)** The thyroid gland has a dual origin. While the main follicular cells develop from the endodermal thyroid diverticulum, the **Parafollicular C cells** (which secrete calcitonin) are derived from the **Ultimobranchial body**. This body is formed by the **4th (and 5th) pharyngeal pouches**, not the 2nd pouch. The 2nd pharyngeal pouch actually gives rise to the palatine tonsils. **2. Analysis of Other Options** * **Option A (Endodermal in nature):** This is true. The thyroid gland is the first endocrine gland to develop (around day 24) from an endodermal thickening in the floor of the primitive pharynx [1]. * **Option B (Foramen caecum forms thyroglossal duct):** This is true. The thyroid primordium descends from the **foramen caecum** (located at the junction of the anterior 2/3 and posterior 1/3 of the tongue) to its final position in the neck via the **thyroglossal duct**, which normally disappears later [1], [2]. * **Option D (Derived from neural crest cells):** This is true. The cells of the ultimobranchial body (which form C cells) are seeded by migrating **neural crest cells**. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Thyroglossal Cyst:** The most common congenital anomaly of the thyroid; it usually presents as a midline, painless, mobile neck swelling that **moves upward on protrusion of the tongue** [2]. * **Ectopic Thyroid:** The most common site is the **Lingual thyroid** (at the base of the tongue), occurring due to failure of descent [2]. * **Pyramidal Lobe:** A common anatomical variant representing a persistent distal end of the thyroglossal duct [1]. * **DiGeorge Syndrome:** Involves defects in the 3rd and 4th pharyngeal pouches, leading to thymic hypoplasia and hypocalcemia (parathyroid defect).

Question 498: Which of the following is NOT pierced during pleural tapping?

A. Parietal pleura
B. Visceral pleura (Correct Answer)
C. Internal intercostal muscle
D. External intercostal muscle

Explanation: Pleural tapping (thoracocentesis) is a clinical procedure performed to remove excess fluid from the **pleural cavity**, which is the potential space located between the parietal and visceral layers of the pleura [3]. **Why Visceral Pleura is the Correct Answer:** The goal of thoracocentesis is to access the pleural space without damaging the underlying lung parenchyma. The **visceral pleura** is the innermost layer that tightly adheres to the surface of the lung [3]. If the needle pierces the visceral pleura, it would enter the lung tissue, potentially causing a pneumothorax (collapsed lung) or hemoptysis. Therefore, the needle must stop once it enters the pleural cavity, leaving the visceral pleura intact. **Why the other options are incorrect (Layers Pierced):** To reach the pleural cavity from the outside, the needle must pass through the following layers in order: 1. Skin and superficial fascia. 2. **External intercostal muscle (Option D):** The outermost muscle layer of the thoracic wall [2]. 3. **Internal intercostal muscle (Option C):** The middle muscle layer. 4. Innermost intercostal muscle. 5. Endothoracic fascia. 6. **Parietal pleura (Option A):** The outer serous layer lining the thoracic cavity [1], [3]. Once this is pierced, the needle enters the pleural fluid. **NEET-PG High-Yield Pearls:** * **Site of Aspiration:** Usually performed in the **8th or 9th intercostal space** in the midaxillary line to avoid the lung and diaphragm. * **Safe Zone:** The needle is always inserted at the **upper border of the lower rib** to avoid damaging the **intercostal neurovascular bundle** (VAN: Vein, Artery, Nerve), which runs in the costal groove at the lower border of the upper rib. * **Nerve Supply:** The parietal pleura is sensitive to pain (innervated by intercostal and phrenic nerves), whereas the visceral pleura is insensitive to pain (autonomic innervation) [1].

Question 499: Streak gonads are seen in which of the following conditions?

A. Turner syndrome (Correct Answer)
B. Klinefelter's syndrome
C. Patau's syndrome
D. Down's syndrome

Explanation: **Explanation:** **1. Why Turner Syndrome is Correct:** Turner syndrome (45, XO) is the most common cause of primary amenorrhea. In these individuals, the absence of the second X chromosome leads to accelerated oocyte atresia. While germ cells migrate to the genital ridge normally during early embryogenesis, they fail to be maintained. By birth or shortly after, the ovaries are replaced by fibrous tissue devoid of follicles, appearing as thin, white, elongated structures known as **"Streak Gonads."** This results in "hypergonadotropic hypogonadism" (low estrogen, high FSH/LH). **2. Why Other Options are Incorrect:** * **Klinefelter's Syndrome (47, XXY):** These individuals have male phenotypes with small, firm testes (not streak gonads). Histology typically shows hyalinization and fibrosis of seminiferous tubules and Leydig cell hyperplasia. * **Patau’s Syndrome (Trisomy 13):** This is a severe multisystemic chromosomal disorder characterized by midline defects (cleft lip/palate, holoprosencephaly) and polydactyly. It does not typically present with streak gonads. * **Down’s Syndrome (Trisomy 21):** While associated with reduced fertility and cryptorchidism in males, it is not characterized by streak gonads. **3. High-Yield NEET-PG Pearls:** * **Karyotype:** 45, XO is the most common, but mosaicism (45,XO/46,XX) can also occur [1]. * **Clinical Features:** Short stature (most common feature), webbed neck (pterygium colli), shield chest (widely spaced nipples), and coarctation of the aorta (pre-ductal) [1]. * **Renal Anomaly:** Horseshoe kidney is frequently associated [1]. * **Hormonal Profile:** Elevated FSH and LH due to lack of negative feedback from estrogen. * **Management:** Growth hormone for stature and estrogen/progesterone for secondary sexual characteristics.

Question 500: Which of the following structures does NOT develop from the mesoderm?

A. Muscles of the bladder
B. Iris muscle (Correct Answer)
C. Deltoid muscle
D. Levator Palpebrae Superioris (LPS) muscle

Explanation: **Explanation:** In embryology, the general rule is that **muscles develop from the mesoderm** (specifically the paraxial and splanchnic mesoderm). However, there are notable exceptions to this rule that are frequently tested in the NEET-PG. **1. Why "Iris Muscle" is the correct answer:** The muscles of the iris (**Sphincter pupillae** and **Dilator pupillae**) are unique because they are derived from the **Neuroectoderm** (specifically the outer layer of the optic cup). Along with the myoepithelial cells of the sweat and mammary glands, these are the rare instances where muscle tissue originates from the ectoderm rather than the mesoderm. **2. Why the other options are incorrect:** * **Muscles of the bladder:** These are smooth muscles (Detrusor muscle) derived from the **splanchnic mesoderm** surrounding the vesical part of the urogenital sinus [1]. * **Deltoid muscle:** This is a skeletal muscle of the limb. All skeletal muscles of the trunk and limbs develop from the **paraxial mesoderm (myotomes)**. * **Levator Palpebrae Superioris (LPS):** This is an extraocular muscle. All extraocular muscles develop from the **pre-otic somitomeres** (mesoderm). **High-Yield Clinical Pearls for NEET-PG:** * **Ectodermal Muscles:** Remember the "Exceptions Rule"—Iris muscles (Sphincter & Dilator pupillae) and Myoepithelial cells are **Ectodermal**. * **Ciliary Muscle:** Unlike the iris muscles, the ciliary muscle is derived from the **mesenchyme (mesoderm)** within the choroid layer [2]. * **Cardiac Muscle:** Derived from **splanchnic mesoderm** (lateral plate mesoderm). * **Tongue Muscles:** All are derived from **occipital myotomes** (mesoderm), except the Palatoglossus (which is derived from the 4th pharyngeal arch mesoderm).

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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