Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 1081: Trigone of urinary bladder develops from:

A. Ectoderm
B. Mesoderm (Correct Answer)
C. None of the options
D. Endoderm of urachus

Explanation: ***Mesoderm*** - The **trigone** of the urinary bladder develops from the **distal ends of the mesonephric (Wolffian) ducts**, which are **mesodermal in origin**. - These ducts are **absorbed into the posterior wall of the bladder**, forming the smooth triangular area between the two ureteric orifices and the internal urethral orifice [1]. - Although the epithelium of the trigone is later **replaced by endodermal epithelium** from the urogenital sinus, the **structural origin remains mesodermal**. - This is a classic example of **epithelial metaplasia** where endodermal epithelium replaces mesodermal tissue. *Endoderm of urachus* - The **urachus** is the fibrous remnant of the allantois that connects the apex of the bladder to the umbilicus. - It forms the **median umbilical ligament** in adults and does **not contribute to the trigone**. - The **urogenital sinus** (endodermal) forms the majority of the bladder body, but not the trigone. *Ectoderm* - The **ectoderm** forms the nervous system, epidermis, and sensory epithelia. - It does **not contribute** to the development of the urinary bladder or its trigone. - The urinary system is derived from **mesoderm** (kidneys, ureters, trigone) and **endoderm** (bladder body, urethra). *None of the options* - This is incorrect because **mesoderm** is the correct embryological origin of the trigone. - The mesonephric ducts that form the trigone are definitively mesodermal structures.

Question 1082: What is the anatomical location of the testis during the 24-28 weeks of intrauterine life?

A. Superficial inguinal ring
B. Inguinal region
C. Scrotal region
D. Deep inguinal ring (Correct Answer)

Explanation: Deep inguinal ring - Between **24-28 weeks of gestation**, the testes are typically located in the **deep inguinal ring**, preparing for their descent into the scrotum. - This stage represents a crucial period in testicular descent, positioning the testes at the entrance to the inguinal canal. *Inguinal region* - While the testes pass through the inguinal region during descent, this term is too broad to pinpoint their exact location at **24-28 weeks**. - The inguinal region encompasses both the **deep and superficial inguinal rings**, as well as the inguinal canal itself. *Scrotal region* - The testes typically reach the **scrotal region** much later, usually by **30-32 weeks of gestation** or shortly before birth. - Their presence in the scrotum at **24-28 weeks** would be considered premature descent. *Superficial inguinal ring* - The testes pass through the **superficial inguinal ring** after traversing the inguinal canal, usually after **28 weeks**, on their way to the scrotum. - Before **28 weeks**, they are generally located more proximally, around the deep inguinal ring.

Question 1083: How many cells are typically present in a morula?

A. 4
B. 8
C. 12
D. 16 (Correct Answer)

Explanation: ***16*** - A **morula** is typically formed around day 3-4 after fertilization and consists of 12-32 cells, with **16 cells** being the **most commonly cited representative number** in embryology textbooks [1]. - This solid ball of cells results from successive **cleavage divisions** of the zygote, and by 16 cells, the characteristic **compaction** is well-established. - The 16-cell stage is the **conventional benchmark** taught in medical education for defining a typical morula [1]. *4* - A 4-cell stage occurs earlier in embryonic development, around the **second day** after fertilization, following the first two cleavage divisions [1]. - This stage precedes the formation of a compact morula. *8* - The 8-cell stage is typically reached by the **third day**, and **compaction begins** at this stage [1]. - While it marks the onset of morula formation, it's generally considered the **early morula** stage rather than the typical or representative cell count. *12* - A 12-cell stage falls within the range for a morula (12-32 cells) and represents an **early-to-mid morula**. - However, **16 cells is more consistently used** as the standard reference point in embryology literature and medical entrance examinations for describing a "typical" morula [1].

Question 1084: From which embryonic layer are glomus cells derived?

A. Surface ectoderm
B. Mesoderm
C. Endoderm
D. Neural crest derivatives (e.g., melanocytes, craniofacial cartilage) (Correct Answer)

Explanation: ***Neural crest derivatives (e.g., melanocytes, craniofacial cartilage)*** - Glomus cells, also known as **chemoreceptor cells** in the carotid and aortic bodies, are derived from the **neural crest** [1]. - The neural crest is a transitory multipotent cell population that arises from the **ectoderm** and migrates extensively to form a wide array of tissues, including neurons, glia, and endocrine cells like glomus cells [1]. *Surface ectoderm* - The surface ectoderm forms the **epidermis**, hair, nails, and glands of the skin, as well as the lens of the eye and inner ear. - It does not give rise to neuroendocrine cells such as glomus cells. *Mesoderm* - The mesoderm forms many tissues including **muscle**, **bone**, connective tissue, the circulatory system, and the urogenital system. - It is not involved in the formation of glomus cells. *Endoderm* - The endoderm forms the **lining of the gastrointestinal and respiratory tracts**, as well as associated glands like the liver and pancreas. - It does not contribute to the development of glomus cells.

Question 1085: Female genital tract develops from?

A. Mesonephric duct
B. Mesonephric tubules
C. Mullerian duct (Correct Answer)
D. None of the options

Explanation: Mullerian duct - The Mullerian (paramesonephric) duct is the primary embryonic structure that gives rise to the fallopian tubes, uterus, cervix, and the upper two-thirds of the vagina in females [1]. - In the absence of Anti-Mullerian Hormone (AMH), which is secreted by the fetal testes, the Mullerian ducts develop into these female reproductive organs [2]. Mesonephric duct - The mesonephric (Wolffian) duct is the precursor to most male internal genital structures, including the epididymis, vas deferens, and seminal vesicles. - In females, the mesonephric duct normally regresses due to the absence of testosterone, leaving only vestigial remnants [2]. Mesonephric tubules - The mesonephric tubules are part of the mesonephros, an embryonic kidney that functions temporarily during development. - While related to the mesonephric duct, these tubules themselves give rise to the efferent ductules in males and largely degenerate in females. None of the options - This option is incorrect because the Mullerian duct specifically forms the female genital tract [1]. - The development of the female reproductive organs is a well-established process originating from this particular embryonic structure.

Question 1086: Ureteric bud arises from?

A. Mullerian duct
B. Mesonephric duct (Correct Answer)
C. Mesonephric tubule
D. Paramesonephric duct

Explanation: ***Mesonephric duct*** - The **ureteric bud** is an outgrowth from the caudal end of the **mesonephric duct** (also known as the Wolffian duct). - This bud plays a crucial role in forming the collecting system of the kidney, including the **ureter**, renal pelvis, calyces, and collecting ducts. *Paramesonephric duct* - The **paramesonephric duct** (or Müllerian duct) develops into the female reproductive tracts (fallopian tubes, uterus, and upper vagina) [1]. - It degenerates in males due to the presence of **Müllerian inhibiting substance (MIS)**. *Mullerian duct* - The **Müllerian duct** is synonymous with the paramesonephric duct [1]. - It does not give rise to any components of the **urinary system**. *Mesonephric tubule* - **Mesonephric tubules** are part of the mesonephros, an embryonic kidney that transiently functions before degenerating. - While they are derived from the same intermediate mesoderm, the ureteric bud grows *out of* the mesonephric duct, not directly from the tubules themselves.

Question 1087: What is the skeletal derivative of the first arch?

A. Stapes
B. Maxilla (Correct Answer)
C. Laryngeal cartilages
D. Hyoid bone

Explanation: Maxilla - The **first pharyngeal arch** forms the maxilla, which is derived from its **dorsal portion**. - This arch also gives rise to the **mandible**, zygoma, and squamous temporal bone. *Stapes* - The **stapes** is a derivative of the **second pharyngeal arch**. - This arch also forms the **styloid process**, lesser horn of the hyoid, and parts of the temporal bone. *Laryngeal cartilages* - The laryngeal cartilages (thyroid, cricoid, arytenoid) are derived from the **fourth and sixth pharyngeal arches**. - These arches give rise to structures involved in the **larynx** and pharynx. *Hyoid bone* - The **hyoid bone** has a dual origin: the **lesser horn and upper body** are from the **second pharyngeal arch**, while the **greater horn and lower body** are from the **third pharyngeal arch**. - It does not exclusively originate from the first arch.

Question 1088: Which of the following structures is NOT derived from the first pharyngeal arch?

A. Mandibular process
B. Frontonasal process (Correct Answer)
C. Both maxillary & mandibular processes
D. Maxillary process

Explanation: **Frontonasal process** - The **frontonasal process** is a distinct embryonic structure that forms the forehead, bridge of the nose, and the primary palate; it is not derived from the pharyngeal arches. - Its development is separate from the pharyngeal arch system, which primarily forms structures of the face, neck, and throat. *Maxillary process* - The **maxillary process** is derived from the first pharyngeal arch and contributes to the formation of the maxilla, zygomatic bone, and part of the temporal bone. - It also forms the lateral components of the upper lip and secondary palate. *Mandibular process* - The **mandibular process** is the ventral portion of the first pharyngeal arch and develops into the mandible (lower jaw). - It also gives rise to the malleus and incus bones of the middle ear and the anterior two-thirds of the tongue. *Both maxillary & mandibular processes* - Both the **maxillary** and **mandibular processes** are direct derivatives of the first pharyngeal arch. - They are fundamental in forming the upper and lower jaws, respectively, along with associated facial structures.

Question 1089: Which embryonic structure gives rise to the 2nd part of the duodenum?

A. Foregut
B. Hindgut
C. Both foregut & midgut (Correct Answer)
D. Midgut

Explanation: ***Both foregut & midgut*** - The **2nd part of the duodenum** (descending part) is derived from **both foregut and midgut** [1]. - The **superior portion** of the 2nd part (above the major duodenal papilla) is derived from the **foregut**. - The **inferior portion** of the 2nd part (below the major duodenal papilla) is derived from the **midgut**. - The **junction between foregut and midgut** occurs **at the major duodenal papilla** (where the bile duct and pancreatic duct enter), which is located in the middle of the 2nd part of the duodenum [1]. - Therefore, the 2nd part straddles both embryonic origins. *Foregut* - The **foregut** gives rise to the pharynx, esophagus, stomach, and the proximal duodenum up to and including the opening of the bile duct. - While the foregut does contribute to the 2nd part of the duodenum, it only forms the **superior portion** above the papilla. - The 1st part and the upper half of the 2nd part are foregut derivatives. *Midgut* - The **midgut** gives rise to the duodenum distal to the bile duct opening, jejunum, ileum, cecum, appendix, ascending colon, and proximal two-thirds of the transverse colon [1]. - While the midgut does contribute to the 2nd part of the duodenum, it only forms the **inferior portion** below the papilla [2]. - The 3rd and 4th parts of the duodenum are entirely midgut derivatives [2]. *Hindgut* - The **hindgut** gives rise to the distal one-third of the transverse colon, descending colon, sigmoid colon, rectum, and superior part of the anal canal [1]. - The duodenum is not derived from the hindgut.

Question 1090: Xiphoid fuses with sternum by what age?

A. 40 years (Correct Answer)
B. 35 years
C. 30 years
D. 45 years

Explanation: ***40 years*** - The **xiphoid process** typically **fuses** with the **sternal body** around the age of **40 years** (range 35-50 years). - This fusion represents the final stage of **sternal ossification** and is a gradual process that occurs during adulthood. - This is the standard age cited in major anatomy textbooks including **Gray's Anatomy** and **Moore's Clinically Oriented Anatomy**. *30 years* - While ossification of the xiphoid process is ongoing in the third decade of life, **30 years** is typically **too early** for complete fusion with the sternal body. - The fusion process usually begins later and is not complete by this age in most individuals. *35 years* - **35 years** represents the **lower end** of the typical range for xiphoid fusion. - While fusion may begin around this age in some individuals, it is not the average or most commonly cited age for completion. *45 years* - **45 years** is within the normal range for xiphoid fusion but represents the **upper end** of the typical timeframe. - Most individuals complete fusion earlier, around age 40.

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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