Embryology and Development — MCQs
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By which week of gestation is the fetal choroidal fissure closed?
Bicornuate uterus is due to:
On what day after fertilization do syncytiotrophoblasts and cytotrophoblasts differentiate?
The prochordal plate marks the site of the future?
During spermiogenesis, which part of the sperm is formed from the mitochondrion of the spermatid?
Primordial germ cells give rise to oogonium and then primary oocyte. PGCs themselves develop from which structure?
A 3-year-old boy is diagnosed as having a persistent processus vaginalis in its middle portion. Which of the following conditions is most likely to be associated with this developmental anomaly?
Which of the following structures gives rise to Gáner's cyst?
From which embryological structure are the intrinsic muscles of the tongue derived?
All of the following participate in male genital tract development except?
Embryology and Development Indian Medical PG Practice Questions and MCQs
Question 221: By which week of gestation is the fetal choroidal fissure closed?
- A. 3rd week
- B. 4th week
- C. 6th week (Correct Answer)
- D. 8th week
Explanation: ### Explanation The development of the eye begins around the 4th week of gestation. The **optic vesicle** invaginates to form a double-layered **optic cup**. This invagination extends along the ventral surface of the optic cup and the optic stalk, forming a groove known as the **choroidal (or optic) fissure**. **Why 6th week is correct:** The primary purpose of the choroidal fissure is to allow the **hyaloid artery** to reach the inner chamber of the eye. Under normal developmental conditions, the margins of this fissure grow toward each other and fuse, surrounding the hyaloid vessels. This fusion begins in the center and spreads anteriorly and posteriorly, completing by the **6th week** of gestation. **Analysis of Incorrect Options:** * **3rd week:** At this stage, the embryo is undergoing gastrulation; the optic primordia (optic grooves) only begin to appear at the end of the 3rd week/start of the 4th week. * **4th week:** This is when the optic vesicle first appears and the choroidal fissure begins to form, not close. * **8th week:** By this time, the fissure should have been closed for two weeks. Delay or failure in closure by this stage results in permanent structural defects. **Clinical Pearls for NEET-PG:** * **Coloboma:** Failure of the choroidal fissure to close results in a Coloboma. It typically occurs in the **inferonasal quadrant** and can affect the iris, ciliary body, retina, or optic nerve. * **Hyaloid Artery:** The distal part of this artery eventually degenerates, while the proximal part persists as the **central artery of the retina**. * **Pax2 Gene:** Mutations in the *PAX2* gene are often associated with optic fissure closure defects (Renal-coloboma syndrome).
Question 222: Bicornuate uterus is due to:
- A. Incomplete fusion of the uterine cavity
- B. Incomplete fusion of the paramesonephric duct (Correct Answer)
- C. Incomplete fusion of the mesonephric duct
- D. Incomplete formation of the vagina
Explanation: Explanation: The development of the female reproductive tract primarily involves the **Paramesonephric (Müllerian) ducts**. In a normal embryo, these ducts undergo a three-stage process: elongation, **midline fusion**, and canalization (septal resorption). [1] **1. Why Option B is Correct:** The uterus, cervix, and upper 1/3rd of the vagina are formed by the fusion of the two paramesonephric ducts [1]. A **Bicornuate Uterus** (heart-shaped uterus) occurs specifically due to the **partial failure of fusion** of the paramesonephric ducts at the superior aspect [2]. This results in two separate uterine horns entering a single cervix. **2. Why Other Options are Wrong:** * **Option A:** Incomplete fusion of the uterine cavity is a vague description. The pathology lies in the fusion of the ducts themselves, not just the internal cavity. * **Option C:** The **Mesonephric (Wolffian) ducts** regress in females due to the absence of testosterone. They contribute to the male reproductive system (epididymis, vas deferens). In females, remnants may persist as Gartner’s cysts. * **Option D:** The vagina has a dual origin. The upper 1/3rd comes from paramesonephric ducts, while the lower 2/3rd comes from the **urogenital sinus** (sino-vaginal bulbs) [1]. Incomplete formation leads to vaginal atresia or agenesis, not a bicornuate uterus. **High-Yield Clinical Pearls for NEET-PG:** * **Septate Uterus:** Failure of **resorption** of the midline septum (most common Mullerian anomaly) [2]. * **Uterus Didelphys:** Complete failure of fusion of paramesonephric ducts (double uterus, double cervix) [3]. * **Mayer-Rokitansky-Küster-Hauser (MRKH) Syndrome:** Müllerian agenesis (absent uterus and upper vagina). * **Renal Anomalies:** Always screen the urinary tract (via ultrasound) in patients with uterine anomalies, as both systems develop from the intermediate mesoderm simultaneously.
Question 223: On what day after fertilization do syncytiotrophoblasts and cytotrophoblasts differentiate?
- A. 6 days
- B. 8 days (Correct Answer)
- C. 10 days
- D. 12 days
Explanation: The differentiation of the trophoblast is a hallmark of the **second week of development**, often referred to as the **"Week of Twos."** Around **Day 8** (shortly after implantation begins), the trophoblast differentiates into two distinct layers [1]: 1. **Cytotrophoblast:** The inner layer of mononucleated cells with distinct cell boundaries (the "cellular" layer). 2. **Syncytiotrophoblast:** The outer, multinucleated zone without distinct cell boundaries that invades the uterine endometrium [1]. **Analysis of Options:** * **Day 6 (Option A):** This is when the blastocyst typically begins to **attach** to the endometrial epithelium. Differentiation into two distinct layers is not yet complete. * **Day 8 (Option B - Correct):** By this day, the blastocyst is partially embedded, and the trophoblast has clearly differentiated into the cyto- and syncytiotrophoblast [1]. Simultaneously, the embryoblast divides into the epiblast and hypoblast [1]. * **Day 10 (Option C):** By this stage, the blastocyst is more deeply embedded, and fibrin coagula close the penetration defect in the surface epithelium. * **Day 12 (Option D):** This period is characterized by the formation of **extraembryonic mesoderm** and the development of lacunar networks within the syncytiotrophoblast to establish uteroplacental circulation [1]. **High-Yield NEET-PG Pearls:** * **Rule of Twos:** 2 trophoblast layers (Cyto/Syncytio), 2 embryoblast layers (Epi/Hypoblast), and 2 cavities (Amniotic/Yolk sac) all form in the 2nd week [1]. * **hCG Production:** The **syncytiotrophoblast** is responsible for secreting Human Chorionic Gonadotropin (hCG), which maintains the corpus luteum [1]. * **Mitosis:** Only cytotrophoblast cells undergo mitosis; they then migrate into the syncytiotrophoblast, where they lose their cell membranes [1].
Question 224: The prochordal plate marks the site of the future?
- A. Umbilical cord
- B. Heart
- C. Mouth (Correct Answer)
- D. Anus
Explanation: The **prochordal plate** (also known as the prechordal plate) is a localized thickening of the hypoblast cells at the cranial end of the embryonic disc. It is formed during the second week of development and serves as a critical organizer for the head region. **1. Why "Mouth" is correct:** The prochordal plate is the site where the ectoderm and endoderm come into direct contact without any intervening mesoderm. This specialized area becomes the **buccopharyngeal membrane** (or oropharyngeal membrane), which eventually ruptures to form the communication between the primitive oral cavity (stomodeum) and the foregut. Thus, it marks the site of the future **mouth**. **2. Why other options are incorrect:** * **Umbilical cord:** This develops from the **connecting stalk**, which contains the allantois and umbilical vessels, located at the caudal end of the embryo initially [1]. * **Heart:** The heart develops from the **cardiogenic area**, which is located cranial to the prochordal plate in the early trilaminar disc before embryonic folding. * **Anus:** The site of the future anus is marked by the **cloacal membrane**, which is located at the caudal (tail) end of the embryonic disc, similar in structure to the prochordal plate (ectoderm-endoderm fusion). **Clinical Pearls & High-Yield Facts:** * **Organizer Role:** The prochordal plate is essential for inducing the development of the forebrain. * **Symmetry:** It establishes the **cranio-caudal axis** and bilateral symmetry of the embryo. * **Mesoderm Exception:** There are only two sites in the trilaminar disc where mesoderm is absent: the **prochordal plate** (cranial) and the **cloacal membrane** (caudal).
Question 225: During spermiogenesis, which part of the sperm is formed from the mitochondrion of the spermatid?
- A. Acrosomal cap
- B. Middle piece (Correct Answer)
- C. Axial filament
- D. Head of the sperm
Explanation: **Explanation:** Spermiogenesis is the final stage of spermatogenesis where non-motile, circular spermatids transform into mature, motile spermatozoa. This process involves significant morphological remodeling of cellular organelles [3]. **1. Why the Correct Answer is Right:** The **Middle piece** of the sperm is formed by the **mitochondria**. During spermiogenesis, the mitochondria relocate and arrange themselves in a tight, spiral sheath (the mitochondrial spiral or *nebenkern*) around the proximal part of the axial filament. This localization is functional: the mitochondria provide the ATP (energy) required for the flagellar movement and motility of the sperm. **2. Why Incorrect Options are Wrong:** * **A. Acrosomal cap:** This is derived from the **Golgi apparatus**. It contains proteolytic enzymes (like acrosin and hyaluronidase) necessary for penetrating the ovum's zona pellucida [1]. * **C. Axial filament:** This forms the core of the tail and is derived from the **distal centriole** of the spermatid. * **D. Head of the sperm:** This is primarily formed by the **nucleus**, which undergoes extreme condensation and elongation, losing most of its cytoplasm. **3. High-Yield Clinical Pearls for NEET-PG:** * **Centrioles:** The proximal centriole enters the egg during fertilization and forms the zygote's first mitotic spindle. The distal centriole forms the axoneme (axial filament). * **Residual Bodies:** Excess cytoplasm discarded during spermiogenesis is termed "residual bodies of Regaud," which are phagocytosed by **Sertoli cells** [2]. * **Kartagener Syndrome:** A clinical correlation involving sperm motility where a defect in the dynein arms of the axial filament leads to immotile cilia and male infertility. [4]
Question 226: Primordial germ cells give rise to oogonium and then primary oocyte. PGCs themselves develop from which structure?
- A. Epiblast (Correct Answer)
- B. Neural crest
- C. Coelomic epithelium
- D. Genital ridge
Explanation: The origin of Primordial Germ Cells (PGCs) is a high-yield embryology concept. While PGCs eventually reside in the gonads, they do not originate there. **1. Why Epiblast is Correct:** During the **second week** of development, PGCs arise from the **epiblast**. During gastrulation (third week), they migrate through the primitive streak and temporarily reside in the **wall of the yolk sac** (near the allantois). Between the fourth and sixth weeks, they migrate via the dorsal mesentery to reach the primitive gonads [1]. **2. Analysis of Incorrect Options:** * **Neural Crest:** These cells give rise to diverse structures like melanocytes, craniofacial cartilage, and the adrenal medulla, but not germ cells. * **Coelomic Epithelium:** This tissue lines the body cavity and contributes to the formation of the **somatic support cells** (Granulosa cells in females and Sertoli cells in males), but not the germ cells themselves. * **Genital Ridge:** This is the **destination**, not the origin. The genital ridge is formed by the proliferation of coelomic epithelium and underlying mesenchyme. PGCs must reach this ridge to induce further gonadal development [2]. **3. NEET-PG High-Yield Pearls:** * **Migration Path:** Epiblast → Yolk sac wall (near allantois) → Dorsal mesentery of hindgut → Genital ridge. * **Clinical Correlation:** If PGCs stray from their migratory path and survive in ectopic sites, they can give rise to **extragonadal teratomas** (most commonly in the sacrococcygeal region). * **Inductive Influence:** If PGCs fail to reach the genital ridge, the gonad fails to develop (gonadal dysgenesis).
Question 227: A 3-year-old boy is diagnosed as having a persistent processus vaginalis in its middle portion. Which of the following conditions is most likely to be associated with this developmental anomaly?
- A. Direct inguinal hernia
- B. Gubernaculum testis
- C. Hematocele
- D. Hydrocele (Correct Answer)
Explanation: ### Explanation **Concept of Processus Vaginalis Development** The **processus vaginalis** is an embryonic developmental outpocketing of the peritoneum that precedes the descent of the testes into the scrotum. Normally, the stalk of this process obliterates, leaving only the distal portion as the **tunica vaginalis** [2]. 1. **Why Hydrocele is Correct:** If the processus vaginalis fails to obliterate completely, it leaves a potential space. When the **middle portion** remains patent (while the proximal and distal ends close), it leads to an accumulation of serous fluid within that segment. This specific clinical entity is known as an **encysted hydrocele of the cord**. If the entire tract remains open, it results in a congenital communicating hydrocele or an indirect inguinal hernia [2]. 2. **Why Other Options are Incorrect:** * **Direct Inguinal Hernia:** This is an acquired defect caused by weakness in the posterior wall of the inguinal canal (Hesselbach’s triangle) [2]. It is not related to the patency of the processus vaginalis. * **Gubernaculum Testis:** This is a mesenchymal structure (a ligamentous cord) that guides the descent of the testis from the posterior abdominal wall to the scrotum [1]. It is not a fluid-filled pathology or a remnant of the processus. * **Hematocele:** This refers to a collection of blood within the tunica vaginalis, usually secondary to trauma, torsion, or malignancy, rather than a developmental patency. **NEET-PG High-Yield Pearls:** * **Indirect Inguinal Hernia:** Occurs due to a **completely patent** processus vaginalis [2]. * **Encysted Hydrocele of the Cord:** Occurs due to patency of the **middle portion** only. * **Congenital Hydrocele:** Fluid communicates with the peritoneal cavity. * **Anatomical Landmark:** The processus vaginalis is located **anteromedial** to the spermatic cord.
Question 228: Which of the following structures gives rise to Gáner's cyst?
- A. Remnant of the paramesonephric duct
- B. Remnant of the mesonephric duct (Correct Answer)
- C. Cervix
- D. Vagina
Explanation: **Explanation:** **Gartner’s cysts** are benign cystic lesions found in the lateral walls of the vagina. They arise from the **remnant of the mesonephric (Wolffian) duct** in females. 1. **Why Option B is Correct:** In female embryos, the absence of testosterone leads to the regression of the mesonephric ducts. However, small vestigial remnants may persist between the layers of the broad ligament or within the vaginal wall [3]. If these remnants become secretory and dilated, they form Gartner’s cysts. 2. **Why Other Options are Incorrect:** * **Option A:** Remnants of the **paramesonephric (Müllerian) duct** in males form the *appendix testis* or the *prostatic utricle*. In females, the paramesonephric ducts normally fuse to form the uterus, cervix, and upper vagina [1]; remnants are rare but can form *Hydatids of Morgagni*. * **Options C & D:** These are anatomical structures, not embryological precursors. While the cyst is located *in* the vaginal wall [2], it originates from the ductal remnant, not the vaginal tissue itself. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Gartner’s cysts are characteristically located in the **anterolateral** wall of the superior vagina [2]. * **Homologue:** The mesonephric duct in males forms the epididymis, vas deferens, and seminal vesicles. * **Other Mesonephric Remnants (Female):** * **Epoophoron:** Located in the mesosalpinx [3]. * **Paroophoron:** Located more medially in the broad ligament [3]. * **Mnemonic:** **G**artner = **G**enital (Wolffian) duct remnant; **M**üllerian = **M**akes the Uterus.
Question 229: From which embryological structure are the intrinsic muscles of the tongue derived?
- A. Second branchial cleft
- B. Pharyngeal arch mesenchyme
- C. Occipital somites (Correct Answer)
- D. Cervical somites
Explanation: The development of the tongue is a complex process involving multiple embryological origins. While the mucous membrane (lining) of the tongue is derived from the pharyngeal arches, the **musculature** follows a different developmental path. **1. Why Occipital Somites are correct:** All muscles of the tongue—both **intrinsic** (superior/inferior longitudinal, transverse, and vertical) and **extrinsic** (genioglossus, hyoglossus, and styloglossus)—except for the Palatoglossus, are derived from the **myotomes of the occipital somites**. During development, these myoblasts migrate ventrally from the occipital region into the tongue primordium. This migration explains why the motor supply to these muscles is the **Hypoglossal nerve (CN XII)**, which is the nerve of the occipital somites. **2. Why other options are incorrect:** * **Second branchial cleft:** Branchial (pharyngeal) clefts are ectodermal indentations that give rise to structures like the external auditory meatus. They do not contribute to muscle formation. * **Pharyngeal arch mesenchyme:** While the pharyngeal arches contribute to the tongue's connective tissue and sensory innervation (e.g., Arch 1 for general sensation, Arch 3 for posterior 1/3), they do not form the tongue's intrinsic muscles. * **Cervical somites:** These give rise to the muscles of the neck and the diaphragm (C3-C5), not the tongue. **High-Yield Clinical Pearls for NEET-PG:** * **The Exception:** The **Palatoglossus** is the only tongue muscle *not* derived from occipital somites; it develops from the 4th pharyngeal arch and is supplied by the **Vagus nerve (CN X)** via the pharyngeal plexus. * **Nerve Supply Rule:** Sensory = Pharyngeal Arches; Motor = Occipital Somites. * **Developmental Landmark:** The *sulcus terminalis* marks the junction between the anterior 2/3 (Arch 1) and posterior 1/3 (Arch 3).
Question 230: All of the following participate in male genital tract development except?
- A. SRY
- B. SOX-9
- C. FGF-9
- D. WNT-4 (Correct Answer)
Explanation: The development of the male genital tract is a complex process driven by specific genetic triggers that divert the bipotential gonad toward a testicular fate. ### **Why WNT-4 is the Correct Answer** **WNT-4** is known as the **"ovary-determining gene."** It is essential for female sexual differentiation. It works by upregulating DAX-1, which antagonizes the male pathway. In the presence of WNT-4, the bipotential gonad develops into an ovary. Therefore, it does not participate in male development; rather, its downregulation is necessary for male differentiation. ### **Analysis of Incorrect Options** * **SRY (Sex-determining Region on Y):** This is the master switch located on the short arm of the Y chromosome. It triggers the differentiation of Sertoli cells and is the primary factor for male development. * **SOX-9:** Acting downstream of SRY, SOX-9 is a critical transcription factor that induces the differentiation of Sertoli cells and the subsequent secretion of Anti-Müllerian Hormone (AMH). * **FGF-9 (Fibroblast Growth Factor 9):** This factor acts in a positive feedback loop with SOX-9. It is essential for the proliferation of Sertoli cells and the migration of mesonephric cells into the gonad to form testis cords. ### **High-Yield Clinical Pearls for NEET-PG** * **Master Gene for Maleness:** SRY gene. * **Master Gene for Femaleness:** WNT-4. * **Sertoli Cells:** Produce **AMH** (causes regression of Müllerian ducts) [1]. * **Leydig Cells:** Produce **Testosterone** (stimulates Wolffian duct development into the epididymis, vas deferens, and seminal vesicles) [1]. * **Dihydrotestosterone (DHT):** Responsible for the development of male external genitalia (penis, scrotum, prostate) [1].
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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