Embryology and Development — MCQs

A 1-year-old girl presents for a routine checkup with a dimpling of the skin in the lumbar region with a tuft of hair growing over the dimple. This condition is seen in 10% to 25% of births and normally has no ill effects. What is this relatively common condition that results from incomplete embryologic development?

Q420Medium

Which trophoblast takes part in invasion of areola during secondary placentation?

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 411: Which of the following structures is derived from the umbilical artery?

A. Ligamentum arteriosum
B. Medial umbilical ligament (Correct Answer)
C. Ligamentum venosum
D. Ligamentum teres

Explanation: The correct answer is **B. Medial umbilical ligament**. ### **Explanation** During fetal life, the **umbilical arteries** carry deoxygenated blood from the fetus to the placenta. After birth, when the umbilical cord is clamped, the distal portions of these arteries lose their function and undergo fibrous degeneration. These obliterated distal segments become the **medial umbilical ligaments**, which are found on the internal surface of the anterior abdominal wall, flanking the urachus [3]. ### **Analysis of Incorrect Options** * **A. Ligamentum arteriosum:** This is the postnatal remnant of the **ductus arteriosus**, which connects the pulmonary artery to the arch of aorta in the fetus to bypass the lungs [3]. * **C. Ligamentum venosum:** This is the remnant of the **ductus venosus**, which shunts oxygenated blood from the left umbilical vein directly to the inferior vena cava (IVC), bypassing the liver [1], [3]. * **D. Ligamentum teres (hepatis):** This is the remnant of the **left umbilical vein**. It is found in the free margin of the falciform ligament [1], [3]. ### **NEET-PG High-Yield Pearls** * **Proximal Umbilical Artery:** Unlike the distal part, the proximal portion remains patent after birth and gives rise to the **superior vesical arteries** (supplying the urinary bladder) [3]. * **Median vs. Medial:** Do not confuse the **Medial** umbilical ligament (remnant of umbilical artery) with the **Median** umbilical ligament (remnant of the **urachus/allantois**) [2]. * **Mnemonic for Remnants:** * **A**rtery $\rightarrow$ **M**edial Ligament (AM) * **V**ein $\rightarrow$ **T**eres (VT) * **D**uctus **A**rteriosus $\rightarrow$ Ligamentum **A**rteriosum (AA) * **D**uctus **V**enosus $\rightarrow$ Ligamentum **V**enosum (VV)

Question 412: During embryological development, all of the following organs develop in the peritoneal cavity suspended on a mesentery, EXCEPT?

A. Liver
B. Spleen
C. Kidney (Correct Answer)
D. Pancreas

Explanation: ### Explanation The core concept tested here is the distinction between **intraperitoneal** and **retroperitoneal** development. **Why Kidney is the Correct Answer:** The **Kidneys** are primarily retroperitoneal organs [2]. They develop from the intermediate mesoderm (metanephros) in the pelvic region and subsequently "ascend" to their lumbar position. Throughout this entire process, they remain behind the parietal peritoneum and are never suspended by a mesentery or located within the peritoneal cavity. **Analysis of Incorrect Options:** * **Liver (A):** Develops within the **ventral mesogastrium** [1]. Although it becomes a massive organ, it remains intraperitoneal, connected to the abdominal wall and stomach by remnants of the mesentery (falciform ligament and lesser omentum). * **Spleen (B):** Develops from mesenchymal cells within the **dorsal mesogastrium**. It remains an intraperitoneal organ throughout life, suspended by the gastrosplenic and lienorenal ligaments. * **Pancreas (D):** This is a high-yield distractor. The pancreas develops from dorsal and ventral buds within the **mesenteries**. While it eventually becomes "secondarily retroperitoneal" (due to the fusion of its mesentery with the posterior abdominal wall), it *originates* suspended in a mesentery, unlike the kidney. **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Retroperitoneal Organs (SAD PUCKER):** **S**uprarenal glands, **A**orta/IVC, **D**uodenum (except 1st part), **P**ancreas (except tail), **U**reters, **C**olon (ascending/descending), **K**idneys [2], **E**sophagus, **R**ectum. 2. **Primary vs. Secondary:** Kidneys are **primarily** retroperitoneal (never had a mesentery) [2]. The Pancreas and parts of the Duodenum are **secondarily** retroperitoneal (lost their mesentery during rotation). 3. The **Spleen** is the only organ in the options derived from **mesoderm** that develops in a mesentery (the others are endodermal foregut derivatives).

Question 413: The septum transversum gives rise to which part of the diaphragm?

A. Right crus
B. Left crus
C. Central tendon (Correct Answer)
D. Peripheral costal portion

Explanation: ### Explanation The diaphragm is a composite structure derived from four distinct embryonic sources. Understanding these is crucial for NEET-PG, as questions frequently focus on the derivatives of each part. **1. Why the Central Tendon is Correct:** The **septum transversum** is a thick plate of mesodermal tissue that initially lies between the primitive thoracic and abdominal cavities. During development, it migrates caudally, carrying the phrenic nerve with it. It eventually thins out to form the **central tendon** of the diaphragm [1]. **2. Why the Other Options are Incorrect:** * **Options A & B (Right and Left Crura):** The crura (and the portion of the diaphragm around the esophagus) develop from the **dorsal mesentery of the esophagus**. * **Option D (Peripheral Costal Portion):** The peripheral muscular part is derived from the **body wall (pleuroperitoneal folds)** and the inward growth of **myoblasts from the body wall** (specifically from the 3rd to 5th cervical somites). **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Diaphragm Development:** "**S**everal **P**arts **B**uild **D**iaphragm" (**S**eptum transversum, **P**leuroperitoneal membranes, **B**ody wall, **D**orsal mesentery of esophagus). * **Congenital Diaphragmatic Hernia (Bochdalek):** Most commonly occurs due to the failure of the **pleuroperitoneal membrane** to fuse, usually on the **left side**. * **Nerve Supply:** The phrenic nerve (C3, C4, C5) supplies the diaphragm because the septum transversum originates in the cervical region before descending. "C3, 4, 5 keep the diaphragm alive." * **Sensory Supply:** The central part is supplied by the phrenic nerve, while the peripheral part is supplied by the lower intercostal nerves.

Question 414: At birth, in which stage is the oocyte of a female child?

A. Anaphase II of meiosis
B. Prophase I of meiosis (Correct Answer)
C. Oogonium
D. Maturation

Explanation: ### Explanation **1. Why Prophase I is correct:** Oogenesis begins during fetal life. Primordial germ cells differentiate into **oogonia**, which then undergo DNA replication to become **primary oocytes**. By the 5th to 7th month of intrauterine life, all primary oocytes enter the first meiotic division (Meiosis I). However, they do not complete this phase; they are arrested in the **Diplotene stage of Prophase I**. [1] This arrest is maintained by Oocyte Maturation Inhibitor (OMI) secreted by follicular cells. The oocytes remain in this "suspended animation" from birth until puberty, when the LH surge triggers the completion of Meiosis I just before ovulation. [2] **2. Why other options are incorrect:** * **Option A (Anaphase II):** This occurs only if fertilization takes place. After puberty, the oocyte completes Meiosis I and enters Meiosis II, but arrests again in **Metaphase II**. It only proceeds to Anaphase II upon sperm penetration. * **Option C (Oogonium):** Oogonia are the stem cells that undergo mitosis. By the 7th month of gestation, almost all oogonia have either transformed into primary oocytes or undergone atresia. No oogonia are present at birth. [1] * **Option D (Maturation):** Maturation is a broad term. Specifically, "Meiotic maturation" refers to the transition from Prophase I to Metaphase II, which happens monthly after puberty, not at birth. **3. NEET-PG High-Yield Pearls:** * **Dictyotene Stage:** Another name for the prolonged diplotene stage where the oocyte is arrested. * **Total Count:** At birth, there are approximately 600,000 to 800,000 primary oocytes. [1] By puberty, only about 40,000 remain. * **The "Two Arrests":** 1. **Birth to Puberty:** Arrested in Prophase I (Diplotene). [1] 2. **Ovulation to Fertilization:** Arrested in Metaphase II.

Question 415: Blastocyst formation occurs after how many days of fertilization?

A. 2-3 days
B. 4-5 days (Correct Answer)
C. 7-9 days
D. 8-11 days

Explanation: **Explanation:** The formation of the blastocyst is a critical milestone in early embryonic development. Following fertilization in the ampulla of the fallopian tube [4], the zygote undergoes a series of mitotic divisions called cleavage [1]. * **Day 1:** Fertilization occurs. * **Day 2-3:** The zygote reaches the 8-cell to 16-cell stage, known as the **Morula** [1]. * **Day 4-5 (Correct Answer):** As the morula enters the uterine cavity, fluid begins to penetrate the zona pellucida, creating a fluid-filled cavity called the **blastocele** [1]. At this stage, the embryo is termed a **Blastocyst**, consisting of an inner cell mass (embryoblast) and an outer cell mass (trophoblast) [1]. * **Day 6-7:** The zona pellucida disappears ("hatching"), and **implantation** begins [3]. **Analysis of Incorrect Options:** * **A (2-3 days):** This corresponds to the cleavage stages and the formation of the **Morula** while the embryo is still in the fallopian tube [1]. * **C (7-9 days):** This is the period when implantation is actively progressing and the blastocyst is becoming embedded in the endometrium [2]. * **D (8-11 days):** By this stage, implantation is nearing completion, and the bilaminar germ disc (epiblast and hypoblast) is well-established [5]. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Blastocyst formation:** Usually occurs as the embryo enters the uterine cavity [1]. * **Hatching:** The blastocyst must "hatch" from the **Zona Pellucida** before implantation can occur [3]. * **Inner Cell mass:** Gives rise to the embryo proper; **Trophoblast:** Gives rise to the placenta [1]. * **Window of Implantation:** Typically between days 20–24 of a standard menstrual cycle [3].

Question 416: Which artery does not participate in the formation of the right subclavian artery?

A. Seventh intersegmental artery
B. All three participate
C. Second aortic arch artery (Correct Answer)
D. Fourth aortic arch artery

Explanation: The development of the aortic arches is a high-yield topic in NEET-PG Anatomy. To understand the formation of the **Right Subclavian Artery**, one must visualize its three distinct embryological segments: [2] 1. **Proximal part:** Derived from the **Right 4th aortic arch**. 2. **Middle part:** Derived from the **Right dorsal aorta** (between the 4th arch and the 7th intersegmental artery). 3. **Distal part:** Derived from the **Right 7th cervical intersegmental artery**. ### Why Option C is Correct The **Second aortic arch artery** does not contribute to the subclavian artery. In fetal development, the second arch largely disappears, leaving behind only the **stapedial** and **hyoid** arteries. ### Analysis of Incorrect Options * **Option A (7th Intersegmental Artery):** This is incorrect because it forms the distal portion of the subclavian artery. As the upper limb bud grows, this artery migrates cranially to become the definitive subclavian. * **Option D (4th Aortic Arch):** This is incorrect because the right 4th arch forms the proximal segment of the right subclavian, while the left 4th arch forms the arch of the aorta (between the left common carotid and left subclavian). * **Option B:** Incorrect, as the second arch is excluded. ### High-Yield Clinical Pearls for NEET-PG * **Left Subclavian Artery:** Unlike the right, the left subclavian is derived *entirely* from the **Left 7th intersegmental artery**. * **Abnormal Right Subclavian Artery (Arteria Lusoria):** Occurs when the right 4th arch and right dorsal aorta disappear [2]. The artery then arises from the descending aorta and passes behind the esophagus, potentially causing **Dysphagia Lusoria**. * **Recurrent Laryngeal Nerve:** The right nerve hooks around the right subclavian (4th arch derivative), while the left hooks around the ligamentum arteriosum (6th arch derivative) [1].

Question 417: The hepatic sinusoids observed histologically in an adult liver are derived from which embryonic structure?

A. Supracardinal veins
B. Anterior cardinal veins
C. Posterior cardinal veins
D. Vitelline veins (Correct Answer)

Explanation: ### Explanation **1. Why Vitelline Veins are Correct:** The liver develops within the **septum transversum** [1]. During the 4th to 5th week of gestation, the rapidly expanding liver cords (derived from the endodermal hepatic diverticulum) invade the surrounding **vitelline veins**. As these cords grow, they break up the proximal part of the vitelline veins into a complex network of vascular channels [3]. These fragmented channels eventually differentiate into the **hepatic sinusoids** [2]. Additionally, the remaining portions of the vitelline veins contribute to the formation of the portal vein and the hepatic portion of the inferior vena cava (IVC). **2. Why the Other Options are Incorrect:** * **Anterior Cardinal Veins (B):** These drain the cephalic part of the embryo and eventually form the internal jugular veins and the superior vena cava (SVC). * **Posterior Cardinal Veins (C):** These primarily drain the trunk of the embryo. Most of the system disappears, with remnants contributing to the root of the azygos vein and common iliac veins. * **Supracardinal Veins (A):** These appear later in development to replace the posterior cardinals. they form the definitive azygos and hemiazygos venous systems. **3. High-Yield Clinical Pearls for NEET-PG:** * **Umbilical Veins:** The left umbilical vein initially carries oxygenated blood from the placenta to the liver. Postnatally, it obliterates to form the **Ligamentum Teres Hepatis**. * **Ductus Venosus:** This is a shunt between the left umbilical vein and the IVC, bypassing the hepatic sinusoids. Postnatally, it becomes the **Ligamentum Venosum**. * **Kupffer Cells:** While sinusoids are vascular (mesodermal), the functional Kupffer cells are derived from **monocytes** (mesoderm) [1], whereas hepatocytes are **endodermal**. * **Sinusoidal Anatomy:** In adults, sinusoids lack a basement membrane and contain large fenestrations to facilitate contact with hepatocytes [4].

Question 418: Which is the largest cell in spermatogenesis?

A. Spermatogonium
B. Primary Spermatocyte (Correct Answer)
C. Secondary spermatocyte
D. Spermatozoa

Explanation: The correct answer is **Primary Spermatocyte**. **1. Why it is the correct answer:** Spermatogenesis begins with spermatogonia, which undergo mitotic division to maintain their population and differentiate into primary spermatocytes [3]. The **primary spermatocyte** is the largest germ cell in the seminiferous tubules. This is because it enters a prolonged **prophase of Meiosis I** (lasting about 22 days), during which it undergoes significant cytoplasmic growth and DNA replication (becoming 4n) to prepare for the first meiotic division [3]. **2. Why the other options are incorrect:** * **Spermatogonium:** These are the stem cells located at the basal lamina. While they are the precursors, they are smaller than the primary spermatocytes they differentiate into. * **Secondary Spermatocyte:** These are formed after the completion of Meiosis I. They are roughly half the size of primary spermatocytes and have a very short lifespan (a few hours) before rapidly entering Meiosis II. * **Spermatozoa:** These are the final, highly condensed functional gametes [2]. Through the process of **spermiogenesis**, they shed most of their cytoplasm and condense their nucleus, making them significantly smaller than their precursor cells [2]. **3. High-Yield Facts for NEET-PG:** * **Ploidy Sequence:** Spermatogonia (2n) → Primary Spermatocyte (2n/4c) → Secondary Spermatocyte (1n/2c) → Spermatid (1n/1c) → Spermatozoa (1n/1c). * **Longest Phase:** The primary spermatocyte stage is the longest phase of spermatogenesis [3]. * **Blood-Testis Barrier:** Primary spermatocytes must pass through the tight junctions of Sertoli cells to move from the basal to the adluminal compartment [1]. * **Spermiogenesis vs. Spermatogenesis:** Remember that *spermiogenesis* is the morphological transformation of a spermatid into a spermatozoon (no cell division involved) [2].

Question 419: A 1-year-old girl presents for a routine checkup with a dimpling of the skin in the lumbar region with a tuft of hair growing over the dimple. This condition is seen in 10% to 25% of births and normally has no ill effects. What is this relatively common condition that results from incomplete embryologic development?

A. Meningomyelocele
B. Meningocele
C. Spina bifida occulta (Correct Answer)
D. Spina bifida cystica

Explanation: ### Explanation **Correct Answer: C. Spina bifida occulta** **1. Why it is correct:** Spina bifida occulta is the mildest and most common form of neural tube defect (NTD). It results from the **failure of the two halves of the vertebral arches to fuse** in the midline, typically in the lumbar or sacral regions (L5 or S1) [3]. Crucially, the spinal cord and meninges remain in their normal position within the vertebral canal. Because the defect is covered by skin, it is "occult" (hidden). The classic clinical markers are a **skin dimple, a tuft of hair (hypertrichosis), a birthmark, or a fatty pad** over the site of the defect. It is usually asymptomatic and often discovered incidentally on X-rays. **2. Why the other options are incorrect:** * **Meningocele (B):** This is a type of *spina bifida cystica* where the meninges protrude through the vertebral defect to form a cyst-like sac filled with CSF [2]. However, the spinal cord remains in its normal position. * **Meningomyelocele (A):** The most severe form of *spina bifida cystica* where both the meninges and the spinal cord/nerve roots protrude into the sac [1], [2]. This leads to significant neurological deficits (e.g., paralysis, bladder dysfunction). * **Spina bifida cystica (D):** This is a broad category that includes both Meningocele and Meningomyelocele. It is characterized by a visible external sac, unlike the "hidden" nature of the occulta variety described in the question. **3. NEET-PG High-Yield Pearls:** * **Embryology:** NTDs result from failure of the neural tube to close during the **4th week** of development. * **Prevention:** Periconceptional supplementation of **Folic acid (400 mcg/day)** significantly reduces the incidence of NTDs. * **Screening:** Elevated **Alpha-fetoprotein (AFP)** in maternal serum and amniotic fluid is a marker for open NTDs (not seen in spina bifida occulta) [2], [3]. * **Association:** Spina bifida occulta is generally benign but can occasionally be associated with **Tethered Cord Syndrome**.

Question 420: Which trophoblast takes part in invasion of areola during secondary placentation?

A. Syncytiotrophoblast
B. Interstitial Extra Villous trophoblast
C. Endovascular Extra Villous trophoblast
D. Interstitial and Endovascular Extra Villous trophoblasts (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Interstitial and Endovascular Extra Villous trophoblasts.** #### 1. Underlying Medical Concept During placentation, the trophoblast differentiates into two main lineages: the **villous trophoblast** (responsible for gas/nutrient exchange) and the **extravillous trophoblast (EVT)** [1]. The EVTs are the "invasive" cells responsible for remodeling the maternal uterine environment [1]. Secondary placentation involves the deep invasion of the maternal decidua and the spiral arteries (often referred to as the "areola" or the junctional zone in specific embryological contexts) [2]. This process requires two distinct subtypes of EVTs: * **Interstitial EVTs:** These cells migrate through the decidual stroma to invade the myometrium and surround the spiral arteries, physically anchoring the placenta [2]. * **Endovascular EVTs:** These cells enter the lumen of the spiral arteries, replacing the maternal endothelial lining and destroying the muscular tunica media [2]. This converts high-resistance vessels into low-resistance, high-capacity channels to ensure adequate fetal blood supply [3]. #### 2. Why Other Options are Wrong * **A. Syncytiotrophoblast:** These are the outer, multinucleated layers of the villi that produce hormones (hCG) and facilitate transport, but they do not migrate or invade deep maternal tissues [1]. * **B & C:** These are incomplete. Both interstitial and endovascular subtypes act in synergy to achieve successful placentation; focusing on only one ignores the dual mechanism of stromal and vascular invasion. #### 3. High-Yield Clinical Pearls for NEET-PG * **Preeclampsia Connection:** Failure of the **Endovascular EVTs** to adequately remodel the spiral arteries (shallow invasion) is the primary pathophysiology behind preeclampsia and fetal growth restriction (FGR). * **Nitabuch’s Layer:** This is a fibrinoid layer formed at the junction of the invading trophoblast and the decidua basalis, preventing over-invasion. * **Placenta Accreta:** Occurs when there is a defect in the decidua, leading to excessive invasion by EVTs into the myometrium [4].

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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