Embryology and Development Practice Questions

Q: Part of neural tube from which corpus callosum develops

Lamina terminalis. ***Lamina terminalis*** - The **lamina terminalis** is a thin membrane that forms the anterior wall of the third ventricle and is a key structure in the development of the **forebrain commissures**, including the **corpus callosum**. - During development, the neurons that form the **corpus callosum** and other commissures cross the midline through the **lamina terminalis** to connect the two cerebral hemispheres. *Basal lamina* - The **basal lamina** is a layer of extracellular matrix that forms part of the basement membrane and provides structural support to epithelial and endothelial cells. - It is not directly involved in the formation of the **corpus callosum** or neural tube development in this specific context. *Alar lamina* - The **alar lamina** (or alar plate) is the dorsal part of the neural tube and is primarily involved in the development of **sensory neurons** and associated structures in the CNS. - It gives rise to the **dorsal horn** of the spinal cord and sensory nuclei in the brainstem, but not the **corpus callosum**. *Basal plate* - The **basal plate** is the ventral part of the neural tube and is primarily involved in the development of **motor neurons** and associated structures in the CNS. - It gives rise to the **ventral horn** of the spinal cord and motor nuclei in the brainstem, but not the **corpus callosum** [1].

Q: Kidney parenchyma is derived from -

Metanephros. Metanephros - The metanephros is the third and definitive kidney that develops embryologically, forming the functional kidney parenchyma. - The metanephric mesenchyme differentiates into the nephrons, including the glomeruli, Bowman's capsule, proximal convoluted tubule, loop of Henle, and distal convoluted tubule. - This represents the true renal parenchyma responsible for filtration and urine formation. Ureteric bud - The ureteric bud is an outgrowth of the mesonephric duct that induces the metanephric mesenchyme to differentiate. - It forms the collecting system: collecting ducts, major and minor calyces, renal pelvis, and ureters. - While essential for kidney development, it does not form the nephrons or kidney parenchyma. Mesonephros - The mesonephros is a transient embryonic kidney that functions during the first trimester before degenerating. - In males, some mesonephric tubules persist as the office-associated structures; in females, they mostly regress. - It does not contribute to the definitive kidney parenchyma. Paramesonephros - The paramesonephric (Müllerian) ducts form the female reproductive tract: fallopian tubes, uterus, and upper vagina. - They play no role in kidney development or renal parenchyma formation.

Q: Female urethra develops from -

Urogenital sinus. ***Urogenital sinus*** - The **urogenital sinus** is an endodermal structure that gives rise to the bladder, urethra, and lower vagina in females [1]. - In females, the entire urethra develops from the **pelvic part of the urogenital sinus**. *Mesonephric duct* - The **mesonephric duct** (Wolffian duct) primarily contributes to the male genital tract, forming structures like the epididymis, vas deferens, and ejaculatory ducts. - In females, the mesonephric ducts largely regress but can contribute to vestigial structures like the **Gartner's duct**. *Ureteric bud* - The **ureteric bud** is an outgrowth of the mesonephric duct that develops into the ureter, renal pelvis, calyces, and collecting ducts of the kidney. - It plays no role in the direct formation of the urethra. *Metanephric blastema* - The **metanephric blastema** is a mesenchymal tissue that interacts with the ureteric bud to form the nephrons, including the renal corpuscle and renal tubules. - It is essential for kidney development but does not contribute to the formation of the urethra.

Q: How many days does it take for a zygote with zona pellucida to reach the uterine cavity after fertilization?

4 days. ***4 days*** - Following fertilization in the **ampulla** of the fallopian tube, the zygote undergoes cleavage divisions as it travels towards the uterus. - The **zona pellucida** remains intact during this journey, and the embryo (typically at the **morula** or early blastocyst stage) enters the uterine cavity around **Day 3-4** post-fertilization. - **Day 4** is the most commonly cited timeframe for entry into the uterine cavity with zona pellucida intact. *2 days* - At 2 days post-fertilization, the embryo is usually in the **2- to 4-cell stage** and is still located within the fallopian tube. - It has not yet completed its journey through the fallopian tube to reach the uterine cavity. *5 days* - By Day 5, the embryo has typically developed into a **blastocyst** and has already been in the uterine cavity for approximately 1-2 days. - This represents a later stage of development after the embryo has already reached the uterine cavity, not the initial arrival time. *6 days* - On Day 6, the blastocyst is typically **hatching out of the zona pellucida** and beginning implantation into the endometrium. - The zona pellucida is no longer intact at this stage, and the embryo has already been in the uterine cavity for approximately 2 days.

Q: Tongue muscles are derived from

Occipital myotome. Occipital myotome - The tongue muscles are innervated by the **hypoglossal nerve (CN XII)**, which is associated with the occipital somites. - During development, **occipital somites** migrate to the floor of the pharynx to form the intrinsic and extrinsic muscles of the tongue. *Lateral plate mesoderm* - The **lateral plate mesoderm** gives rise to structures like the lining of the body cavities, the serous membranes, and the smooth muscle and connective tissue of the gut wall, but not skeletal muscles of the tongue. - It also forms the **cardiac muscle** and most of the limb connective tissues. *Intermediate mesoderm* - The **intermediate mesoderm** differentiates into the urogenital system, including the kidneys, gonads, and their ducts. - It plays no direct role in the formation of skeletal muscles like those found in the tongue. *Cervical myotome* - **Cervical myotomes** contribute to the formation of muscles in the neck and diaphragm, such as the trapezius, sternocleidomastoid, and diaphragm muscles. - They do not contribute to the development of the tongue muscles, which are derived from more caudal somites.

Q: Erythropoiesis starts in the yolk sac during which weeks of fetal development?

2-4 weeks. ***2-4 weeks*** - Erythropoiesis in the **yolk sac** begins around the **3rd week** of development (specifically around day 19-21), which falls within the 2-4 week timeframe [1]. - This is the **mesoblastic stage** of hematopoiesis, representing the earliest phase of blood cell formation. - The yolk sac produces **primitive nucleated erythrocytes** [1] and continues as the primary site until approximately the **8th week**. - This is the correct answer as it captures the initial onset period. *4-6 weeks* - While yolk sac erythropoiesis is still active during this period, the **initial onset** occurs earlier, specifically starting in **week 3**. - By weeks 4-6, the process is well-established but has already started. *6-8 weeks* - By 6-8 weeks, the **hepatic phase** begins, with the **liver** starting to take over as the primary site of erythropoiesis. - The yolk sac activity begins to decline during this period. - This represents continuation, not the start, of yolk sac erythropoiesis. *8-10 weeks* - By 8-10 weeks, the **liver** has become the **dominant site** of erythropoiesis. - The yolk sac contribution is minimal or ceased by this time. - This is far too late to represent when erythropoiesis **starts** in the yolk sac.

Q: Fertilization usually occurs in which part of fallopian tube?

Ampulla. ***Ampulla*** - The **ampulla** is the widest and longest part of the fallopian tube, making it the most common site for **fertilization** to occur. - Sperm typically meet the oocyte here after ovulation and transport through the fimbriae. *Fimbrial end* - The **fimbriae** are finger-like projections at the end of the fallopian tube that **capture the ovulated oocyte**. - While essential for collecting the egg, it is not the primary site where fertilization takes place. *Interstitium* - The **interstitium** (or intramural part) is the segment of the fallopian tube that passes through the **uterine wall**. - It is too narrow and close to the uterus for fertilization to normally occur there. *Isthmus* - The **isthmus** is the narrow, muscular part of the fallopian tube connecting the ampulla to the uterus. - While sperm may reside here for a short period before fertilization, it is not the typical site where the sperm and egg unite.

Q: Which of the following is not a derivative of the middle ear cleft?

Semicircular canal. Semicircular canal - The **semicircular canals** are part of the **bony labyrinth** of the inner ear, derived from the **otic vesicle**, not the middle ear cleft. [1] - They are involved in **balance** and detecting **rotational head movements**. [1] *Mastoid air cell* - The **mastoid air cells** are pneumatic spaces that develop as extensions of the **mastoid antrum**, which is part of the **middle ear cleft**. - They develop after birth and are continuous with the **tympanic cavity**. *Tympanic cavity* - The **tympanic cavity**, or middle ear proper, is the central component of the **middle ear cleft**, housing the ossicles. [1] - It develops from the expanded proximal part of the **first pharyngeal pouch**. *Eustachian tube* - The **Eustachian tube** (auditory tube) connects the middle ear to the nasopharynx and is derived from the **first pharyngeal pouch**, making it a component of the **middle ear cleft**. [1] - Its function is to **equalize pressure** across the tympanic membrane. [1]

Q: On which day after fertilization does the blastocyst hatch from the zona pellucida?

4-7 days. ***4-7 days*** - The **blastocyst** typically **hatches from the zona pellucida** around **day 5-6** post-fertilization (within the 4-7 day range) [1]. - After hatching, the blastocyst is free to interact with the endometrium and **begins implantation** around **day 6-7** [1]. - This hatching process is essential for successful implantation and **embryo-endometrial synchrony** [2]. *10-12 days* - By 10-12 days post-fertilization, the blastocyst has already hatched and implantation is well underway [3]. - At this stage, the **trophoblast** has differentiated into syncytiotrophoblast and cytotrophoblast, and the **bilaminar embryonic disc** is forming [3]. *12-15 days* - This timeframe is well beyond blastocyst hatching, which occurs around day 5-6. - At this stage, the **trilaminar embryonic disc** (gastrulation) and early placental structures are developing [3]. *15-20 days* - This period marks significant **embryonic development** and early **organogenesis**, far past the stage of blastocyst hatching. - The missed menstrual period is typically recognized around this time, confirming pregnancy.

Q: When is the first polar body formed during oogenesis?

First meiotic division. ***First meiotic division*** - The **first polar body** is extruded at the completion of the **first meiotic division** when the primary oocyte divides into a secondary oocyte and the first polar body. - This division is unequal, ensuring the secondary oocyte retains most of the cytoplasm and nutrients essential for future development. *Mitosis* - **Mitosis** is the process where oogonia (germline stem cells) proliferate to form primary oocytes *before* birth. - It results in two identical daughter cells and does not involve the formation of polar bodies. *Second meiotic division* - The **second polar body** is formed upon completion of the **second meiotic division**, which occurs *after fertilization*. - The second meiotic division is triggered when the secondary oocyte is penetrated by a sperm. *Fertilization* - **Fertilization** is the fusion of sperm and egg, which triggers the completion of the **second meiotic division** and the expulsion of the second polar body. - The first polar body has already been formed before fertilization occurs.

Question 1

Part of neural tube from which corpus callosum develops

Accepted Answer

Lamina terminalis

Answer

Basal lamina

Answer

Alar lamina

Answer

Basal plate

Question 2

Kidney parenchyma is derived from -

Accepted Answer

Metanephros

Answer

Ureteric bud

Answer

Mesonephros

Answer

Paramesonephros

Question 3

Female urethra develops from -

Accepted Answer

Urogenital sinus

Answer

Mesonephric duct

Answer

Ureteric bud

Answer

Metanephric blastema

Question 4

How many days does it take for a zygote with zona pellucida to reach the uterine cavity after fertilization?

Accepted Answer

4 days

Answer

2 days

Answer

5 days

Answer

6 days

Question 5

Tongue muscles are derived from

Accepted Answer

Occipital myotome

Answer

Lateral plate mesoderm

Answer

Intermediate mesoderm

Answer

Cervical myotome

Question 6

Erythropoiesis starts in the yolk sac during which weeks of fetal development?

Accepted Answer

2-4 weeks

Answer

4-6 weeks

Answer

6-8 weeks

Answer

8-10 weeks

Question 7

Fertilization usually occurs in which part of fallopian tube?

Accepted Answer

Ampulla

Answer

Fimbrial end

Answer

Interstitium

Answer

Isthmus

Question 8

Which of the following is not a derivative of the middle ear cleft?

Accepted Answer

Semicircular canal

Answer

Tympanic cavity

Answer

Eustachian tube

Answer

Mastoid air cell

Question 9

On which day after fertilization does the blastocyst hatch from the zona pellucida?

Accepted Answer

4-7 days

Answer

10-12 days

Answer

12-15 days

Answer

15-20 days

Question 10

When is the first polar body formed during oogenesis?

Accepted Answer

First meiotic division

Answer

Second meiotic division

Answer

Mitosis

Answer

Fertilization

Embryology and Development — MCQs

Embryology and Development — MCQs

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