Embryology and Development Practice Questions

Q: Which of the following structures is not derived from the ectoderm?

Eustachian tube. ***Eustachian tube*** - The **Eustachian tube** (auditory tube) is derived from the **endoderm**, specifically from the first pharyngeal pouch. - It connects the nasopharynx to the middle ear and is responsible for equalizing pressure [1]. *Lens* - The **lens** of the eye develops from the surface ectoderm through an invagination called the **lens placode**. - This ectodermal origin is crucial for its transparency and refractive properties. *Brain* - The **brain** is a primary derivative of the ectoderm, specifically the **neural tube**, which forms from the neural plate during neurulation. - This ectodermal origin gives rise to the entire central nervous system. *Retina* - The **retina** of the eye, along with the optic nerve, develops from the **neuroectoderm** (a part of the neural tube). - Its ectodermal origin is essential for its light-sensing function.

Q: Haploid number of chromosomes is first seen in?

Secondary spermatocyte. ***Secondary spermatocyte*** - A secondary spermatocyte is formed after **meiosis I**, where the homologous chromosomes are separated, resulting in a cell with a **haploid number of chromosomes (n)**, although each chromosome still consists of two sister chromatids. - This is the **first stage** where haploidy is achieved in spermatogenesis. - These cells are transient and quickly undergo meiosis II to form spermatids. *Spermatogonia* - Spermatogonia are **diploid (2n)** germline stem cells that undergo mitosis to produce more spermatogonia or differentiate into primary spermatocytes. - They contain the full complement of chromosomes found in somatic cells. *Primary spermatocytes* - Primary spermatocytes are also **diploid (2n)** cells that enter meiosis I. - Before meiosis I, DNA replication occurs, so each chromosome consists of two sister chromatids, but the cell still maintains a diploid chromosome number. *Spermatids* - Spermatids are formed after **meiosis II** from secondary spermatocytes and are also **haploid (n)**. - However, secondary spermatocytes become haploid **earlier** in the process, immediately following the reductional division of meiosis I.

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: 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: 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: 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: Skeletal derivative of 2nd pharyngeal arch -

Stapes. ***Stapes*** - The **2nd pharyngeal arch** (also known as the hyoid arch) gives rise to several structures, including Reichert's cartilage, which forms the **stapes** bone, the styloid process, the lesser horn of the hyoid, and the upper part of the hyoid body. - Its muscles include the **stapedius**, stylohyoid, posterior belly of the digastric, and muscles of facial expression. *Malleus* - The **malleus** is derived from the **1st pharyngeal arch** (Meckel's cartilage), along with the incus. - The 1st pharyngeal arch is also responsible for forming the malleus, incus, and mandible. *Incus* - Similar to the malleus, the **incus** also originates from the **1st pharyngeal arch** (Meckel's cartilage). - Both the malleus and incus are crucial components of the middle ear ossicles but are structurally distinct from the stapes. *Maxilla* - The **maxilla** development is primarily from the **maxillary prominence** of the first pharyngeal arch, which is a subdivision of the first arch but does not originate from the 2nd arch. - It forms a significant portion of the midface and upper jaw, contributing to the nasal cavity and orbital floor.

Q: Which of the following is derived from endoderm?

Gall bladder. ***Gall bladder*** - The **gallbladder**, along with other organs of the **gastrointestinal tract** such as the liver, pancreas, and epithelial lining of the digestive and respiratory systems, originates from the **endoderm** [1]. - The endoderm forms the primitive gut tube, from which these accessory digestive organs bud off. *Lens* - The **lens of the eye** is derived from the **surface ectoderm**, which invaginates to form the lens vesicle. - This contrasts with the neural ectoderm, which forms the neural tube and retina. *Spleen* - The **spleen** is derived from the **mesoderm**, specifically from mesenchymal cells in the dorsal mesentery of the stomach. - It is involved in blood filtration and immune responses, making it a lymphoid organ. *Lymph nodes* - **Lymph nodes** are primarily derived from the **mesoderm**, specifically from specialized mesenchymal cells that form their connective tissue capsule and stroma. - The immune cells within the lymph nodes, such as lymphocytes, originate from hematopoietic stem cells that migrate into these developing structures.

Q: Inferior parathyroid develops from which pharyngeal pouch?

3rd. The inferior parathyroid glands develop from the dorsal wing of the third pharyngeal pouch. Due to their origin, they often migrate further caudally than the superior parathyroid glands, sometimes even locating within the thymus which also develops from the third pouch. *1st* - The first pharyngeal pouch contributes to the formation of the eustachian tube, tympanic cavity, and mastoid air cells. - It has no role in the development of the parathyroid glands. *2nd* - The second pharyngeal pouch mainly gives rise to the palatine tonsils and their crypts. - It is not involved in the development of parathyroid tissue. *4th* - The fourth pharyngeal pouch gives rise to the superior parathyroid glands and the parafollicular cells (C cells) of the thyroid, which produce calcitonin. - While it forms parathyroid tissue, it is for the superior glands, not the inferior ones.

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.

Question 1

Which of the following structures is not derived from the ectoderm?

Accepted Answer

Eustachian tube

Answer

Brain

Answer

Retina

Answer

Lens

Question 2

Haploid number of chromosomes is first seen in?

Accepted Answer

Secondary spermatocyte

Answer

Spermatogonia

Answer

Primary spermatocytes

Answer

Spermatids

Question 3

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 4

Blastocyst makes contact with endometrium on ?

Accepted Answer

5 - 7 days

Answer

< 3 days

Answer

8 - 11 days

Answer

15-16 days

Question 5

What is the outer layer of the blastocyst called?

Accepted Answer

Trophoblast

Answer

Embryo proper

Answer

Primitive streak

Answer

Yolk sac

Question 6

Which structure do cytotrophoblasts invade during implantation?

Accepted Answer

Decidua basalis

Answer

Decidua capsularis

Answer

Decidua vera

Answer

Decidua parietalis

Question 7

Skeletal derivative of 2nd pharyngeal arch -

Accepted Answer

Stapes

Answer

Malleus

Answer

Incus

Answer

Maxilla

Question 8

Which of the following is derived from endoderm?

Accepted Answer

Gall bladder

Answer

Lens

Answer

Spleen

Answer

Lymph nodes

Question 9

Inferior parathyroid develops from which pharyngeal pouch?

Accepted Answer

3rd

Answer

1st

Answer

2nd

Answer

4th

Question 10

Coronary sinus develops from?

Accepted Answer

Sinus venosus

Answer

Truncus arteriosus

Answer

Conus

Answer

AV canal

Embryology and Development — MCQs

Embryology and Development — MCQs

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