Embryology and Development Practice Questions

Q: What is a characteristic feature observed in a fetus at approximately 12 weeks of gestation?

Limbs well formed. ***Limbs well formed*** - By **12 weeks gestation**, the limbs are well formed, with fingers and toes identifiable, although movements are often still subtle and not yet felt by the mother. - This stage marks significant progression in **skeletal and muscular development**, allowing for more defined body structures [1]. *Nails are visible* - **Nail development** typically begins around **12-13 weeks**, but they are usually not clearly or distinctly visible until much later in gestation, often around **20 weeks or more**. - At 12 weeks, the focus is on the basic formation of digits rather than the intricate details of nail plates. *Anus is seen as dark spot* - The formation of the **anus and anal canal** occurs much earlier in embryonic development, around weeks 7-8, following the separation of the cloaca. - While present, it's not a characteristic feature that uniquely distinguishes the 12-week stage; its visibility as a "dark spot" is not a primary developmental landmark at this specific point. *Meconium is found in duodenum* - **Meconium formation** involves the accumulation of swallowed amniotic fluid, shed cells, and gastrointestinal secretions, which typically starts around **12-16 weeks** [2] but primarily collects in the large intestine. - Although the digestive system is developing, the primary accumulation of meconium and its typical presence in the duodenum as a notable feature is not characteristic of the 12-week mark.

Q: Which of the following is not a neural plate inducer?

High BMP. High BMP - **Bone Morphogenetic Proteins (BMPs)** are primarily involved in promoting epidermal differentiation in the ectoderm, and actively **inhibiting neural differentiation**. - Therefore, high levels of BMP would **prevent neural plate formation**, rather than induce it. *FGF upregulation* - **Fibroblast Growth Factors (FGFs)** are crucial in the early development of the nervous system. - They play a key role in **inducing neural plate formation** and maintaining its identity. *Prechordal mesoderm* - The **prechordal mesoderm**, located anterior to the notochord, is an important signalling center during early embryonic development. - It contributes to the **induction of the forebrain** and plays a role in patterning the anterior neural plate. *Notochord appearance* - The **notochord**, a transient rod-like structure, is a primary inducer of the neural plate. - It secretes factors like **Sonic Hedgehog (Shh)** which induce the overlying ectoderm to differentiate into neuroectoderm, forming the neural plate.

Q: Which structure do cytotrophoblasts invade during implantation?

Decidua basalis. ***Decidua basalis*** - The **cytotrophoblasts** invade the maternal **decidua basalis**, which is the portion of the **endometrium** directly underlying the implanted embryo, forming the maternal component of the **placenta**. - This invasion is crucial for establishing the **placenta** and allowing for nutrient and waste exchange between the mother and the fetus. *Decidua parietalis* - The **decidua parietalis** is the portion of the **endometrium** lining the rest of the **uterine cavity**, not directly involved in the immediate implantation site. - It plays a role later in pregnancy, fusing with the **decidua capsularis** as the **embryo** grows. *Decidua capsularis* - The **decidua capsularis** is the portion of the endometrium that overlies the implanted embryo, separating it from the uterine lumen. - It does not undergo invasion by the **cytotrophoblasts** in the same way the **decidua basalis** does. *Decidua vera* - The **decidua vera** is another term for the **decidua parietalis**, referring to the endometrial lining of the uterine cavity that is not involved in the implantation site. - It is not directly invaded by **cytotrophoblasts** during implantation.

Q: Pancreas divisum indicates which of the following?

Failure of fusion of dorsal & ventral pancreatic buds. ***Failure of fusion of dorsal & ventral pancreatic buds*** - **Pancreas divisum** is a congenital anomaly where the **dorsal and ventral pancreatic buds fail to fuse** during embryonic development [1]. - This results in the **bulk of the pancreas (dorsal bud)** draining through the **accessory pancreatic duct** into the minor duodenal papilla, while the ventral bud drains via the main pancreatic duct [1]. *Duplication of the pancreas* - This condition involves the presence of **multiple, distinct pancreatic tissues**, which is different from pancreas divisum where the existing buds simply do not fuse. - Pancreas divisum is a failure of fusion of two normally formed buds, not the formation of extra pancreatic tissue. *Formation of more than two pancreatic buds* - Normal embryonic development typically involves two pancreatic buds (dorsal and ventral), not more than two [1]. - The issue in pancreas divisum is with the **fusion process**, not the number of initial buds [1]. *Formation of only one pancreatic bud* - Pancreatic development normally involves **two distinct buds (dorsal and ventral)** [1]. - The formation of only one bud would lead to pancreatic agenesis or severe hypoplasia, which is a different anomaly than pancreas divisum.

Q: Development of labia majora is from -

Genital swelling. ***Genital swelling*** - The **labia majora** develop from the **genital (labioscrotal) swellings** in females, which are homologous to the scrotum in males [3]. - These swellings enlarge and fuse anteriorly to form the mons pubis and posteriorly to form the posterior commissures of the labia majora. *Urogenital sinus* - The **urogenital sinus** gives rise to structures like the **bladder**, **urethra**, and parts of the **vagina** in females [2]. - It does not contribute to the formation of the external labial structures. *Mullerian duct* - The **Mullerian (paramesonephric) ducts** develop into the **fallopian tubes**, **uterus**, and the **upper third of the vagina** [1], [2]. - These structures are internal reproductive organs and do not form external genitalia like the labia majora. *Genital ridge* - The **genital ridge** is the embryonic precursor to the **gonads** (ovaries or testes). - It differentiates into either ovaries or testes and does not directly form external genital structures.

Q: Coronary sinus develops from?

Sinus venosus. Sinus venosus - The sinus venosus is a primordial cardiac chamber that receives venous blood from the body and placenta in the early embryonic heart. - The left horn of the sinus venosus loses its connection with the systemic venous circulation and becomes the coronary sinus, which drains most of the cardiac veins into the right atrium [1, 4]. Truncus arteriosus - The truncus arteriosus is the embryonic precursor to the ascending aorta and pulmonary trunk. - It does not contribute to the development of the coronary sinus. Conus - The conus (or conus cordis) is the outflow portion of the primitive ventricle and differentiates into the outflow tracts of the right (infundibulum) and left (aortic vestibule) ventricles. - It is not involved in the formation of the coronary sinus. AV canal - The atrioventricular (AV) canal connects the primitive atrium and ventricle and is crucial for the formation of the AV valves and septation of the heart chambers. - It does not directly develop into the coronary sinus.

Q: What is the outer layer of the blastocyst called?

Trophoblast. ***Trophoblast*** - The **trophoblast** is the outer layer of cells of the blastocyst, which goes on to form the **placenta** and other extraembryonic tissues [1]. - It plays a crucial role in the **implantation** of the blastocyst into the uterine wall and in producing hormones [1]. *Primitive streak* - The **primitive streak** is a structure that forms during **gastrulation**, much later than the initial blastocyst stage. - It establishes the **anterior-posterior axis** and initiates the formation of the three germ layers. *Yolk sac* - The **yolk sac** is an extraembryonic membrane that forms within the blastocyst cavity, but it is not the outermost layer of the entire structure. - It is involved in early **nutrient transfer** and **blood cell formation** before the placenta is fully functional. *Embryo proper* - The **embryo proper**, derived from the **inner cell mass (ICM)**, is the part of the blastocyst that will develop into the actual embryo [2]. - It is located *inside* the trophoblast layer, not forming the outer boundary of the blastocyst [2].

Q: Blastocyst makes contact with endometrium on ?

5 - 7 days. ***5-7 days*** - The **blastocyst makes initial contact** (apposition) with the **endometrium** around **day 5-6 after fertilization**. - **Implantation**, which includes adhesion and invasion, typically begins around day 6 and is complete by day 10. - This timeframe allows the blastocyst to travel from the fallopian tube to the uterus and for the uterine lining to be optimally prepared. *< 3 days* - Within the first few days after fertilization, the zygote is still undergoing **cleavage** and development into a **morula**, then a young blastocyst, while traveling down the fallopian tube. - It has not yet reached the uterus or developed sufficiently to interact with the endometrium. *8-11 days* - By 8-11 days, the process of implantation is usually **well underway or completed**, with the blastocyst already invading the endometrial wall. - Initial contact and attachment occur prior to this period. *15-16 days* - This timeframe is well beyond the typical window for initial blastocyst contact and implantation. - By 15-16 days post-fertilization, the embryo would be undergoing **gastrulation** and early organogenesis, assuming successful implantation.

Q: Bronchogenic sequestration is seen in which lobe?

Left lower lobe. ***Left lower lobe*** - **Bronchopulmonary sequestration**, particularly the **intralobar type**, most commonly affects the **posterior basal segment of the left lower lobe**. [1] - This congenital malformation involves a segment of lung tissue that lacks normal communication with the tracheobronchial tree and receives its blood supply from a systemic artery. [1] *Right upper lobe* - While sequestration can occur anywhere, the **right upper lobe** is a much less common location for bronchopulmonary sequestration compared to the lower lobes. - Sequestration in the upper lobes is rare and usually associated with specific anatomical variations. *Right middle lobe* - The **right middle lobe** is also an infrequent site for bronchopulmonary sequestration. - The typical presentation involves the basal segments of the lower lobes due to embryonic developmental patterns. *Left upper lobe* - **Left upper lobe** involvement in bronchopulmonary sequestration is uncommon. - The majority of cases are found in the lower lobes, especially the left lower lobe.

Q: What is the classification of the Y chromosome?

Submetacentric. ***Submetacentric*** - The **Y chromosome** is classified as submetacentric because its **centromere** is located off-center, resulting in two arms of unequal length. - The short arm (Yp) is smaller than the long arm (Yq), but not as disproportionate as in acrocentric chromosomes. - The **X chromosome** is also submetacentric, making both sex chromosomes belong to this category. *Metacentric* - A **metacentric chromosome** has its **centromere** located in the middle, resulting in two arms of approximately equal length. - Examples include chromosomes 1, 3, 16, 19, and 20, which have nearly equal arm ratios unlike the Y chromosome. *Acrocentric* - An **acrocentric chromosome** has its **centromere** located very close to one end, creating one very short arm and one very long arm. - The five acrocentric human chromosomes are **13, 14, 15, 21, and 22**, which possess satellite DNA and nucleolar organizing regions (NORs) on their short arms. - The **Y chromosome is NOT acrocentric** despite historical confusion; it has a more centrally positioned centromere than true acrocentric chromosomes. *None of the options* - This option is incorrect because the Y chromosome has a specific and well-established classification as **submetacentric** based on its centromere position and arm ratio.

Question 1

What is a characteristic feature observed in a fetus at approximately 12 weeks of gestation?

Accepted Answer

Limbs well formed

Answer

Anus is seen as dark spot

Answer

Meconium is found in duodenum

Answer

Nails are visible

Question 2

Which of the following is not a neural plate inducer?

Accepted Answer

High BMP

Answer

FGF upregulation

Answer

Prechordal mesoderm

Answer

Notochord appearance

Question 3

Which structure do cytotrophoblasts invade during implantation?

Accepted Answer

Decidua basalis

Answer

Decidua capsularis

Answer

Decidua vera

Answer

Decidua parietalis

Question 4

Pancreas divisum indicates which of the following?

Accepted Answer

Failure of fusion of dorsal & ventral pancreatic buds

Answer

Duplication of the pancreas

Answer

Formation of more than two pancreatic buds

Answer

Formation of only one pancreatic bud

Question 5

Development of labia majora is from -

Accepted Answer

Genital swelling

Answer

Urogenital sinus

Answer

Mullerian duct

Answer

Genital ridge

Question 6

Coronary sinus develops from?

Accepted Answer

Sinus venosus

Answer

Truncus arteriosus

Answer

Conus

Answer

AV canal

Question 7

What is the outer layer of the blastocyst called?

Accepted Answer

Trophoblast

Answer

Embryo proper

Answer

Primitive streak

Answer

Yolk sac

Question 8

Blastocyst makes contact with endometrium on ?

Accepted Answer

5 - 7 days

Answer

< 3 days

Answer

8 - 11 days

Answer

15-16 days

Question 9

Bronchogenic sequestration is seen in which lobe?

Accepted Answer

Left lower lobe

Answer

Right upper lobe

Answer

Left upper lobe

Answer

Right middle lobe

Question 10

What is the classification of the Y chromosome?

Accepted Answer

Submetacentric

Answer

Metacentric

Answer

Acrocentric

Answer

None of the options

Embryology and Development — MCQs

Embryology and Development — MCQs

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