Embryology and Development — MCQs
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Fusion of the caudal portions of the kidneys during embryonic development is most likely to result in which of the following congenital conditions?
The testis descends the inguinal canal during which month of gestation?
The fourth ventricle develops from which embryonic structure?
In a sperm cell, where are the mitochondria located?
The head of a sperm is derived from which cellular organelle?
The stomach is derived from which embryonic structure?
By which stage does the zona pellucida disappear?
Which of the following events is involved in cleavage of the zygote during week 1 of development?
Anencephaly occurs due to the inability of the neural tube to close at which week of intrauterine life?
Which structure is formed by the structure indicated by the arrow?
Embryology and Development Indian Medical PG Practice Questions and MCQs
Question 961: Fusion of the caudal portions of the kidneys during embryonic development is most likely to result in which of the following congenital conditions?
- A. Bicornuate uterus
- B. Cryptorchidism
- C. Horseshoe kidney (Correct Answer)
- D. Hypospadias
Explanation: **Explanation:** **1. Why Horseshoe Kidney is Correct:** The **Horseshoe kidney** is the most common renal fusion anomaly. It occurs during the 7th to 9th week of gestation when the lower poles (caudal portions) of the metanephric blastema fuse across the midline before the kidneys ascend from the pelvis to the lumbar region. As the fused kidney attempts to ascend, it is trapped by the **Inferior Mesenteric Artery (IMA)** at the level of L3, which prevents it from reaching its normal adult position. **2. Why the Other Options are Incorrect:** * **Bicornuate uterus:** This results from the incomplete fusion of the **Paramesonephric (Müllerian) ducts** in the female fetus, not the renal blastema. * **Cryptorchidism:** This refers to undescended testes, caused by failure of the testes to migrate from the abdomen into the scrotum. It is related to the gubernaculum and hormonal factors, not renal fusion. * **Hypospadias:** This is a failure of the **urethral folds** to fuse on the ventral surface of the penis, leading to an abnormal urethral opening. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vascular Trap:** The ascent of a horseshoe kidney is arrested by the **Inferior Mesenteric Artery (IMA)**. * **Position:** It is usually located at the level of **L3–L5** vertebrae. * **Associated Risks:** Patients have an increased risk of **nephrolithiasis** (due to stasis), **hydronephrosis** (due to PUJ obstruction), and **Wilms tumor** in children. * **Syndromic Association:** Frequently associated with **Turner Syndrome** (45, XO).
Question 962: The testis descends the inguinal canal during which month of gestation?
- A. 5th
- B. 6th
- C. 7th (Correct Answer)
- D. 8th
Explanation: The descent of the testis is a complex physiological process regulated by hormones (Androgens and MIS) and the contraction of the **gubernaculum**. This process occurs in distinct stages based on gestational age: **1. Why 7th Month is Correct:** The descent occurs in three major phases: * **Trimester 1 (End of 2nd month):** The testes reach the iliac fossa. * **Trimester 2 (3rd to 7th month):** They remain at the deep inguinal ring. * **7th Month:** This is the critical period where the testis **traverses the inguinal canal**. By the end of the 7th month (approx. 28 weeks), the testis reaches the superficial inguinal ring. **2. Analysis of Incorrect Options:** * **5th & 6th Month:** During this period, the testes are located intra-abdominally near the deep inguinal ring. They have not yet entered the canal. * **8th Month:** By the 8th month, the testis has usually passed through the canal and is entering the scrotum. It typically reaches the final scrotal position by the **9th month** (just before birth). **3. NEET-PG High-Yield Facts:** * **Gubernaculum:** The mesenchymal structure that guides the descent. Its remnant in adults is the **scrotal ligament**. * **Processus Vaginalis:** An evagination of peritoneum that precedes the testis; failure of this to obliterate leads to **Congenital Hydrocele** or **Indirect Inguinal Hernia**. * **Cryptorchidism:** Failure of descent, most commonly arrested in the **inguinal canal**. * **Ectopic Testis:** Most common site is the **superficial inguinal pouch**. * **Hormonal Control:** The transabdominal phase is controlled by **Insulin-like peptide 3 (INSL3)**, while the inguinoscrotal phase is **Androgen-dependent**.
Question 963: The fourth ventricle develops from which embryonic structure?
- A. Telencephalon
- B. Mesencephalon
- C. Diencephalon
- D. Rhombencephalon (Correct Answer)
Explanation: ### Explanation The development of the ventricular system is intrinsically linked to the differentiation of the primary brain vesicles. The correct answer is **Rhombencephalon** (Hindbrain). #### 1. Why Rhombencephalon is Correct During the 4th week of development, the neural tube forms three primary vesicles. The most caudal vesicle, the **Rhombencephalon**, further divides into the **metencephalon** (pons and cerebellum) and the **myelencephalon** (medulla). The cavity within these two secondary vesicles expands and flattens to form the **fourth ventricle** [1]. #### 2. Analysis of Incorrect Options * **A. Telencephalon:** This is a derivative of the Prosencephalon (forebrain). Its cavity develops into the **Lateral ventricles**. * **B. Mesencephalon:** This vesicle does not divide further. Its narrow cavity becomes the **Cerebral Aqueduct (of Sylvius)**, which connects the third and fourth ventricles [2]. * **C. Diencephalon:** Also a derivative of the Prosencephalon. Its cavity forms the slit-like **Third ventricle**. #### 3. NEET-PG High-Yield Pearls * **Foramina of the 4th Ventricle:** Cerebrospinal fluid (CSF) exits the fourth ventricle into the subarachnoid space via the median **Foramen of Magendie** and the two lateral **Foramina of Luschka** [3] (*Mnemonic: **M**agendie is **M**idline; **L**uschka is **L**ateral*). * **Rhombic Lips:** These are specialized elevations of the alar plates in the metencephalon that give rise to the **Cerebellum** [2]. * **Hydrocephalus:** Obstruction of the Cerebral Aqueduct (the narrowest part of the system) leads to non-communicating hydrocephalus, dilating the third and lateral ventricles [3].
Question 964: In a sperm cell, where are the mitochondria located?
- A. Head
- B. Neck
- C. Body (Correct Answer)
- D. Tail
Explanation: ### Explanation The mature human spermatozoon is divided into three main parts: the head, the neck, and the tail (which includes the middle piece, principal piece, and end piece) [1]. **Why the "Body" (Middle Piece) is correct:** The **Middle Piece** (often referred to as the **Body**) contains a central core of longitudinal microtubules (the axoneme) surrounded by a spiral column of **mitochondria** (mitochondrial sheath). These mitochondria are essential for aerobic metabolism, providing the **ATP (Adenosine Triphosphate)** required for the motility of the flagellum [1], [3]. **Analysis of Incorrect Options:** * **Head:** Primarily contains the **haploid nucleus** (condensed genetic material) and the **acrosome** [1]. The acrosome is a lysosome-like organelle containing enzymes (hyaluronidase and acrosin) necessary for penetrating the ovum’s zona pellucida [2]. * **Neck:** This is the constricted region containing the **centrioles** (proximal and distal). * **Tail:** While the middle piece is technically the proximal part of the tail, the **Principal Piece** and **End Piece** consist mainly of the axoneme and fibrous sheath, lacking mitochondria. **High-Yield NEET-PG Pearls:** 1. **Mitochondrial Inheritance:** All mitochondria in a sperm cell are located in the middle piece. During fertilization, this part usually does not enter the oocyte, or if it does, the paternal mitochondria are selectively degraded. Thus, **mitochondrial DNA is inherited exclusively from the mother**. 2. **Kartagener Syndrome:** A clinical condition involving dynein arm defects in the sperm tail (and cilia), leading to **immotile spermatozoa** and male infertility [3]. 3. **Acrosome Origin:** The acrosome is derived from the **Golgi apparatus** during spermiogenesis.
Question 965: The head of a sperm is derived from which cellular organelle?
- A. Golgi body
- B. Nucleus (Correct Answer)
- C. Mitochondria
- D. Centromere
Explanation: The process of **spermiogenesis** involves the transformation of a circular spermatid into a specialized, motile spermatozoon [1]. The mature sperm is divided into a head, neck, middle piece, and tail. ### 1. Why the Nucleus is Correct The **head of the sperm** is primarily composed of the **nucleus**, which contains highly condensed haploid chromatin (DNA). During development, the nucleus undergoes significant remodeling where histones are replaced by protamines to ensure the genetic material is packed tightly for transport. The anterior two-thirds of this nucleus is covered by the **acrosome**, which acts as a "cap" [3]. ### 2. Analysis of Incorrect Options * **Golgi Body:** While the Golgi body is essential, it forms the **acrosomal cap** (containing enzymes like hyaluronidase), not the head itself [3]. * **Mitochondria:** These aggregate in the **middle piece** (sheath of axial filament) to provide the ATP required for sperm motility. * **Centromere/Centriole:** The distal centriole gives rise to the **axial filament (axoneme)** of the tail, while the proximal centriole is donated to the oocyte during fertilization [2]. ### 3. High-Yield Clinical Pearls for NEET-PG * **Acrosome Reaction:** This is the release of enzymes from the Golgi-derived acrosomal cap to penetrate the *zona pellucida* [2]. * **Mitochondrial Inheritance:** Sperm mitochondria are located in the neck/middle piece and are usually shed or degraded upon fertilization; thus, mitochondrial DNA is inherited **maternally**. * **Kartagener Syndrome:** A high-yield clinical correlation where a defect in the dynein arms of the sperm tail (axoneme) leads to male infertility due to immotile sperm.
Question 966: The stomach is derived from which embryonic structure?
- A. Foregut (Correct Answer)
- B. Midgut
- C. Hindgut
- D. Allantois
Explanation: **Explanation:** The gastrointestinal tract develops from the primitive gut tube, which is divided into the foregut, midgut, and hindgut [1] based on its arterial supply. **1. Why Foregut is Correct:** The **stomach** develops from the **distal part of the foregut**. During the 4th week of development, the stomach appears as a fusiform dilation. It subsequently undergoes a 90° clockwise rotation around its longitudinal axis and a secondary rotation around its anteroposterior axis, which determines the final position of the greater and lesser curvatures and the formation of the lesser sac (omental bursa). The foregut is supplied by the **celiac trunk**. **2. Why Incorrect Options are Wrong:** * **Midgut:** This segment gives rise to structures from the distal half of the duodenum (below the opening of the common bile duct) to the proximal two-thirds of the transverse colon [1]. It is supplied by the **superior mesenteric artery**. * **Hindgut:** This segment forms the distal one-third of the transverse colon down to the superior part of the anal canal [1]. It is supplied by the **inferior mesenteric artery**. * **Allantois:** This is an extra-embryonic sac involved in early fluid exchange and bladder development; its remnant becomes the **urachus** (median umbilical ligament) [1]. **Clinical Pearls for NEET-PG:** * **Hypertrophic Pyloric Stenosis:** A high-yield clinical condition involving the stomach, characterized by non-bilious projectile vomiting and an "olive-shaped" mass. * **Vagus Nerve Supply:** Due to the 90° clockwise rotation, the **left vagus** nerve supplies the **anterior** wall of the stomach, and the **right vagus** supplies the **posterior** wall [2]. * **Epithelium:** The lining of the entire gut tube (including the stomach) is derived from **endoderm**, while the muscular and serous layers are derived from **splanchnic mesoderm**.
Question 967: By which stage does the zona pellucida disappear?
- A. Before fertilization
- B. During fertilization
- C. 5th day after fertilization (Correct Answer)
- D. 7th day after fertilization
Explanation: ### Explanation The **Zona Pellucida (ZP)** is a specialized glycoprotein shell surrounding the oocyte and the early embryo. Its disappearance, known as **"Hatching,"** is a critical step for successful implantation. **Why Option C is Correct:** After fertilization, the zygote undergoes cleavage while traveling through the fallopian tube. By the **4th day**, it becomes a **morula** and enters the uterine cavity [1]. By the **5th day**, fluid accumulation transforms it into a **blastocyst**. At this stage, the blastocyst must "hatch" from the rigid zona pellucida to allow for rapid growth and to expose the underlying trophoblast cells for attachment to the uterine endometrium [2]. If the ZP does not disappear by the 5th day, implantation cannot occur. **Why Other Options are Incorrect:** * **Option A & B:** The ZP is essential during these stages. It contains species-specific sperm receptors (ZP3) that facilitate fertilization and undergoes the **"Zona Reaction"** immediately after the first sperm enters to prevent polyspermy [1]. It also prevents the blastomeres from dissociating during early cleavage [1]. * **Option D:** By the 7th day, the blastocyst has already begun the process of **implantation** (which typically starts on day 6) [2]. If the ZP were still present on day 7, the embryo would be unable to adhere to the decidua. ### NEET-PG High-Yield Pearls: * **Function of ZP:** Prevents **ectopic implantation** by ensuring the embryo does not stick to the fallopian tube walls. * **Hatching Mechanism:** Occurs due to the secretion of proteases (trypsin-like enzymes) by the trophoblast and the rhythmic expansion-contraction of the blastocyst. * **Clinical Correlation:** In IVF, "Assisted Hatching" (using lasers or chemicals to thin the ZP) is sometimes performed to improve implantation rates in older women or those with thickened ZP.
Question 968: Which of the following events is involved in cleavage of the zygote during week 1 of development?
- A. A series of mitotic divisions forming blastomeres
- B. Production of highly undifferentiated blastomeres
- C. A decreased cytoplasmic content of blastomeres
- D. A decrease in size of blastomeres (Correct Answer)
Explanation: Cleavage is a series of rapid mitotic divisions that occur as the zygote travels through the uterine tube toward the uterus. The defining characteristic of cleavage is that it occurs within the confines of the rigid **Zona Pellucida** [1]. **1. Why the Correct Answer is Right:** During cleavage, the total volume of the embryo remains constant because the Zona Pellucida prevents expansion [1]. Consequently, with each successive mitotic division, the resulting daughter cells (**blastomeres**) become progressively **smaller** [1]. This increases the surface-area-to-volume ratio, facilitating efficient nutrient exchange before implantation. **2. Analysis of Incorrect Options:** * **Option A:** While cleavage *is* a series of mitotic divisions, the question asks for the specific *event* or consequence involved. While technically true, "decrease in size" is the more specific physiological hallmark of cleavage emphasized in embryology. * **Option B:** Blastomeres are not "highly undifferentiated" in the sense of being random; they undergo **compaction** (at the 8-cell stage) where they maximize contact and begin the first differentiation into the inner cell mass and trophoblast [1]. * **Option C:** The *total* cytoplasmic content of the embryo remains relatively stable; it is partitioned into smaller units [1]. The nuclear-to-cytoplasmic ratio actually **increases** as DNA replicates while the total cytoplasm does not. **Clinical Pearls for NEET-PG:** * **Compaction:** Occurs at the **8-cell stage**, mediated by **E-cadherin**. This is the first step in segregation of cell lineages. * **Morula:** Formed at the **16-cell stage** (approx. Day 3) [1]. * **Blastocyst:** Formed when a cavity (blastocele) appears (approx. Day 4) [2]. * **Hatching:** The blastocyst must "hatch" from the Zona Pellucida to implant; failure to hatch results in infertility, while premature hatching can lead to ectopic pregnancy [2].
Question 969: Anencephaly occurs due to the inability of the neural tube to close at which week of intrauterine life?
- A. 2nd week
- B. 3rd week
- C. 4th week (Correct Answer)
- D. 5th week
Explanation: ***4th week***- The development of the **neural tube** occurs during the 4th week of intrauterine life, with the **anterior neuropore** normally closing around day 25 after conception. - Failure of this anterior closure, specifically at the cranial end during the 4th week, results in the severe congenital anomaly known as **anencephaly** [1].*3rd week*- The 3rd week is when **neurulation** (the folding of the neural plate) is initiated and the neural groove is formed, not when the final critical closure occurs.- The developing embryo is undergoing **gastrulation** during the 3rd week (formation of the three germ layers), preceding the completion of neural tube closure.*5th week*- By the 5th week, the neural tube is typically completely closed, and the process of **primary brain vesiculation** (forebrain, midbrain, hindbrain) is actively underway.- A closure defect leading to anencephaly would have necessarily occurred earlier, during the 4th week.*2nd week*- The 2nd week of development is characterized by the formation of the **bilaminar germ disc** (epiblast and hypoblast) and implantation.- **neurulation** (the process that forms the neural tube) does not begin until the start of the 3rd week, making the 2nd week too early for this specific closure defect.
Question 970: Which structure is formed by the structure indicated by the arrow?
- A. Nucleus pulposus (Correct Answer)
- B. Annulus fibrosus
- C. Septum transversum
- D. Neural tube
Explanation: ***Nucleus pulposus*** - The arrow indicates the **notochord**, a midline mesodermal rod that serves as the basis of the axial skeleton. Its postnatal remnant is the **nucleus pulposus**. - The **nucleus pulposus** is the gelatinous inner core of the intervertebral disc, responsible for providing shock absorption and flexibility to the vertebral column. *Annulus fibrosus* - The **annulus fibrosus** is the strong, fibrocartilaginous outer layer of the intervertebral disc that surrounds the nucleus pulposus. - It is derived from the **sclerotome** portion of the somites, not the notochord. *Neural tube* - The **neural tube**, shown as the large purple structure dorsal to the notochord, develops into the central nervous system (brain and spinal cord). - It is formed from the folding of the **neuroectoderm**, a process induced by the underlying notochord, but it is a distinct structure. *Septum transversum* - The **septum transversum** is a mass of mesodermal tissue that develops more cranially and ventrally in the embryo. - It is a major embryonic precursor to the central tendon of the **diaphragm** and does not originate from the notochord.
Practice by Chapter
Gametogenesis and Fertilization
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Early Embryonic Development
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Development of Gastrointestinal System
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Development of Head and Neck
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Congenital Anomalies
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Molecular Mechanisms in Development
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