Embryology and Development Practice Questions

Q: Embryo gets implanted at what stage of development?

Blastocyst. Blastocyst - Implantation into the uterine wall occurs when the embryo has developed into a blastocyst, typically around day 6 post-fertilization [1]. - The blastocyst consists of an inner cell mass (which forms the embryo) and an outer layer called the trophoblast (which contributes to the placenta) [1]. Two cell stage - This stage occurs very early in development, usually within the first 24-30 hours after fertilization [1]. - At this point, the embryo is still in the fallopian tube and has not yet reached the uterus for implantation [1]. Four cell stage - The four-cell stage is also an early cleavage stage, occurring around 2 days post-fertilization [1]. - Like the two-cell stage, the embryo is still in transport through the fallopian tube and is not ready for implantation [1]. Morula - The morula is a solid ball of cells formed by cleavage, typically around day 3-4 post-fertilization [1]. - While it has moved closer to the uterus, it has not yet formed the distinct inner cell mass and trophoblast necessary for successful implantation [1].

Q: Which of the following statements about keratinocytes is true?

They are derived from the ectoderm.. ***They are derived from the ectoderm.*** - **Keratinocytes**, the predominant cell type in the epidermis, originate from the **ectodermal germ layer** during embryonic development. - The ectoderm gives rise to the nervous system, epidermis, and other external structures of the body. *Keratinocytes remain unchanged as they progress through the layers of the epidermis.* - Keratinocytes undergo significant **morphological and functional changes** as they migrate from the basal layer to the stratum corneum, a process called **keratinization** [1]. - These changes include the accumulation of **keratin filaments**, loss of organelles, and flattening of cells [1]. *Keratinocytes are only found in the basal and spinous layers of the epidermis.* - Keratinocytes are found in **all four to five layers** of the epidermis, from the deepest **stratum basale** to the most superficial **stratum corneum** [1]. - They are the primary cells that form the protective barrier of the skin. *Keratinocytes only differentiate in the stratum corneum layer.* - **Differentiation of keratinocytes** begins in the **stratum basale** (where they divide) and continues through the **stratum spinosum** and **stratum granulosum** as they mature and accumulate keratin [1]. - The stratum corneum primarily consists of **dead, fully differentiated keratinocytes** (corneocytes).

Q: Which of the following structures is present in an XY child but absent in an XX child?

Prostate gland. ***Prostate gland*** - The **prostate gland** is the most characteristic male-specific accessory reproductive organ that is **definitively present in XY and absent in XX individuals**. - It develops from the **urogenital sinus** under the influence of **dihydrotestosterone (DHT)** during embryonic development. - The prostate is a **substantial glandular structure** that surrounds the urethra and produces approximately 30% of seminal fluid. - It has **no homologous structure in females**—there is no female equivalent organ. *Incorrect: Urethral glands (Cowper's glands)* - **Cowper's glands (bulbourethral glands)** are indeed male-specific structures present only in XY individuals. - However, they are **homologous to Bartholin's glands** in females—meaning both develop from similar embryonic tissue (urogenital sinus). - While the question technically could accept this answer, the **prostate gland is the more definitive answer** as it is larger, more clinically significant, and has no female homologue. - Cowper's glands are small pea-sized glands that contribute to pre-ejaculate fluid. *Incorrect: Ovaries* - **Ovaries** are the primary female gonads present in **XX individuals**, not XY individuals [1]. - They produce ova and female sex hormones (estrogen and progesterone) [1]. - In XY individuals, the **testes** develop instead under the influence of the SRY gene. *Incorrect: Vestibular glands (Bartholin's glands)* - **Bartholin's glands** are female-specific structures present in **XX individuals**, not XY individuals. - Located at the posterior vaginal opening, they secrete mucus for vaginal lubrication. - They are homologous to Cowper's glands in males but are distinct structures.

Q: When does the rudimentary cochlea develop in the fetus?

4th to 8th week. 4th to 8th week - The **cochlea** begins its development from the **otic vesicle** around the **4th week** of gestation and undergoes extensive coiling. - By the **8th week**, the cochlea has achieved its characteristic snail-like shape, though further differentiation and maturation continue. *First week* - The first week of embryonic development involves **fertilization**, **cleavage**, and **implantation**, with no organogenesis occurring [1]. - At this stage, the embryo is a **blastocyst**, and specific organ structures like the cochlea have not yet begun to form [1]. *8th to 12th week* - While significant maturation of the inner ear structures occurs during this period, the **rudimentary cochlea** has already formed its basic shape by the 8th week. - This phase involves further differentiation of the **organ of Corti** and development of neural connections, rather than the initial formation of the cochlea itself. *16 to 20th week* - By the 16th to 20th week, the inner ear structures are largely developed and functional, including the **cochlea**, which is capable of responding to sound stimuli. - This period marks the onset of **fetal hearing** and continued fine-tuning of the auditory system, far beyond the rudimentary stage of cochlear development.

Q: External auditory canal is formed by:

1st branchial groove. 1st branchial groove - The **external auditory canal** is primarily derived from the **first branchial (pharyngeal) groove** during embryonic development [1]. - This groove deepens to form the primitive external auditory meatus, which later develops into the adult external auditory canal [1]. *1st visceral pouch* - The **first pharyngeal (visceral) pouch** gives rise to structures like the **eustachian tube** (auditory tube) and the **middle ear cavity** (tympanic cavity) [1]. - It does not contribute to the formation of the external auditory canal. *2nd branchial groove* - The **second pharyngeal (branchial) groove** contributes to the formation of the **cervical sinus**, which normally obliterates. - Persistence of this groove can lead to **cervical cysts or fistulae**, but it is not involved in ear development. *2nd visceral pouch* - The **second pharyngeal (visceral) pouch** develops into the **palatine tonsils** and its fossa. - It plays no role in the formation of the external auditory canal or other ear structures.

Q: Trigone of bladder is derived from?

Mesonephric duct. The trigone of the bladder is formed from the caudal ends of the **mesonephric ducts**, which are absorbed into the primitive bladder wall [1]. This mesenchymal origin explains why the trigone has a smooth lining [1] and is less prone to infection compared to the rest of the bladder. *Paramesonephric duct* - The **paramesonephric ducts** (Müllerian ducts) are involved in forming the female reproductive organs, specifically the fallopian tubes, uterus [2], and upper vagina. - They do not contribute to the formation of the urinary bladder or its trigone. *Absorbed anal membrane* - The **anal membrane** separates the endoderm-derived hindgut from the ectoderm-derived anal pit. - Its absorption is relevant to the development of the anus, not the urinary bladder. *Mullerian duct* - The **Müllerian ducts** are synonymous with the paramesonephric ducts and are primarily involved in the development of the female reproductive tract [2]. - They play no role in the development of the urinary bladder or its trigone.

Q: Where do primitive red blood cells first originate during early embryonic development?

Yolk sac. ***Yolk sac*** - The **yolk sac** is the primary site of **hematopoiesis** during the first few weeks of embryonic development. - Primitive erythroid cells (red blood cells) originate here to supply the developing embryo with oxygen. *Liver* - The **liver** takes over as the main hematopoietic organ from about the 6th week of gestation, after the yolk sac [1]. - While it produces various blood cells, it is not the *first* site of primitive red blood cell formation. *Bone marrow* - **Bone marrow** becomes the primary site of hematopoiesis during the **fetal period** (around the 20th to 24th week) and continues throughout postnatal life [2]. - It is not involved in the initial production of primitive red blood cell formation in early embryogenesis. *Spleen* - The **spleen** plays a minor role in fetal hematopoiesis, mainly producing lymphoid cells and some myeloid cells, and can take on myeloid functions if the bone marrow is compromised. - It is not the initial site of red blood cell production in the early embryo.

Q: Which of the following is not a derivative of foregut?

Cecum. ***Cecum*** - The **cecum** and the entire large intestine (except the distal third of the transverse colon) are derivatives of the **midgut** [1]. - The midgut is supplied by the **superior mesenteric artery**, differentiating it developmentally from the foregut. *First part of the duodenum* - The **first part of the duodenum** (from the pylorus to the major duodenal papilla) is derived from the **foregut**. - This section receives its blood supply from branches of the **celiac trunk**, consistent with its foregut origin. *Liver* - The **liver** develops as a budding from the distal foregut and is therefore a **foregut derivative** [2]. - It plays a crucial role in metabolism and detoxification, consistent with its early development from this segment. *Pancreas* - The **pancreas** develops from dorsal and ventral buds of the distal foregut, making it a **foregut derivative**. - Both its exocrine and endocrine functions are vital for digestion and glucose homeostasis.

Q: Sertoli cells are derived from -

Coelomic epithelium. Sertoli cells are derived from the **coelomic epithelium** (surface epithelium) of the urogenital ridge during gonadal development. - The coelomic epithelium proliferates to form the **primitive sex cords** (medullary cords in males), and cells within these cords differentiate into Sertoli cells. - These cells are essential for **spermatogenesis**, providing structural support and nutrition to developing germ cells, and producing **anti-Müllerian hormone (AMH)** which causes regression of Müllerian ducts in male development [1]. *Germinal epithelium* - This is an **outdated term** previously used for the surface epithelium of the gonad, based on the misconception that it gave rise to germ cells. - Modern embryology uses the term **coelomic epithelium** or surface epithelium instead. - While historically used, this terminology is no longer preferred in current medical literature. *Genital swelling* - **Genital swellings** (labioscrotal swellings) are external mesodermal structures that develop into the **scrotum** in males or **labia majora** in females. - These are external genitalia components and are not the source of internal testicular cells like Sertoli cells. *Primordial germ cells* - **Primordial germ cells (PGCs)** originate from the epiblast, migrate via the hindgut to the developing gonads, and differentiate into **spermatogonia** (males) or **oogonia** (females) [1]. - They form the **germ cell lineage** (gametes), not somatic support cells like Sertoli cells, which are of coelomic epithelial origin.

Q: Which type of glial cell is derived from mesodermal origin?

Microglial cells. ***Microglial cells*** - **Microglial cells** are unique among glial cells as they originate from **mesoderm**, specifically from **monocyte/macrophage precursors** in the bone marrow [1]. - They function as the **immune cells of the central nervous system (CNS)**, scavenging for plaques, damaged neurons, and infectious agents [1]. *Macroglial cells* - This is a broad category that includes **astrocytes, oligodendrocytes, and ependymal cells**, all of which are derived from **neuroectoderm**, not mesoderm [1]. - They perform various supportive roles but are distinct in origin from microglial cells [1]. *Oligodendrocytes* - **Oligodendrocytes** are derived from **neuroectoderm** and are responsible for forming the **myelin sheath** around axons in the CNS [2]. - Myelination is crucial for rapid and efficient nerve impulse conduction. *Ependymal cells* - **Ependymal cells** are derived from **neuroectoderm** and line the **ventricles of the brain** and the **central canal of the spinal cord**. - They play a role in the production and circulation of **cerebrospinal fluid (CSF)**.

Question 1

Embryo gets implanted at what stage of development?

Accepted Answer

Blastocyst

Answer

Two cell stage

Answer

Four cell stage

Answer

Morula

Question 2

Which of the following statements about keratinocytes is true?

Accepted Answer

They are derived from the ectoderm.

Answer

Keratinocytes remain unchanged as they progress through the layers of the epidermis.

Answer

Keratinocytes are only found in the basal and spinous layers of the epidermis.

Answer

Keratinocytes only differentiate in the stratum corneum layer.

Question 3

Which of the following structures is present in an XY child but absent in an XX child?

Accepted Answer

Prostate gland

Answer

Urethral glands (Cowper's glands)

Answer

Ovaries

Answer

Vestibular glands (Bartholin's glands)

Question 4

When does the rudimentary cochlea develop in the fetus?

Accepted Answer

4th to 8th week

Answer

First week

Answer

8th to 12th week

Answer

16 to 20th week

Question 5

External auditory canal is formed by:

Accepted Answer

1st branchial groove

Answer

1st visceral pouch

Answer

2nd branchial groove

Answer

2nd visceral pouch

Question 6

Trigone of bladder is derived from?

Accepted Answer

Mesonephric duct

Answer

Paramesonephric duct

Answer

Absorbed anal membrane

Answer

Mullerian duct

Question 7

Where do primitive red blood cells first originate during early embryonic development?

Accepted Answer

Yolk sac

Answer

Liver

Answer

Bone marrow

Answer

Spleen

Question 8

Which of the following is not a derivative of foregut?

Accepted Answer

Cecum

Answer

Liver

Answer

Pancreas

Answer

First part of the duodenum

Question 9

Sertoli cells are derived from -

Accepted Answer

Coelomic epithelium

Answer

Genital swelling

Answer

Primordial germ cells

Answer

Germinal epithelium

Question 10

Which type of glial cell is derived from mesodermal origin?

Accepted Answer

Microglial cells

Answer

Macroglial cells

Answer

Oligodendrocytes

Answer

Ependymal cells

Embryology and Development — MCQs

Embryology and Development — MCQs

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