Embryology and Development Practice Questions

Q: Defect in any of the following results in renal agenesis, except:

Failure of descent of kidney into the lumbar region. The development of the permanent kidney (metanephros) depends on a reciprocal inductive interaction between two key structures: the **Ureteric Bud** and the **Metanephric Blastema**. [1] ### 1. Why Option D is Correct **Failure of descent (Ectopic Kidney)** is a positional anomaly, not a developmental failure of the organ itself. The kidney initially develops in the pelvic region and "ascends" to the lumbar region due to the straightening of the fetal body and differential growth. If this migration fails, the kidney remains in the pelvis (Pelvic Kidney). While the position is abnormal, the renal tissue is present and functional [1]; therefore, it does **not** result in renal agenesis. ### 2. Why Other Options are Incorrect * **Ureteric Bud (Option B) & Nephrogenic Bud (Option A):** These terms refer to the outgrowth from the mesonephric duct. The ureteric bud induces the surrounding mesoderm to form nephrons. If the bud fails to develop or reach the mesoderm, the kidney will not form (Renal Agenesis). * **Blastema of Nephrogenic Tissue (Option C):** Also known as the Metanephric Blastema, this provides the cells that form the nephrons (Bowman’s capsule, PCT, Loop of Henle, and DCT). Without this tissue, there is no substrate for the ureteric bud to induce, leading to agenesis. [1] ### 3. NEET-PG High-Yield Pearls * **Derivatives:** The **Ureteric Bud** gives rise to the collecting system (Ureter, Renal Pelvis, Calyces, and Collecting ducts). The **Metanephric Blastema** gives rise to the excretory system (Nephrons). * **Potter Sequence:** Bilateral renal agenesis leads to oligohydramnios, resulting in pulmonary hypoplasia, limb deformities, and characteristic facial features. * **Most Common Ectopic Kidney:** Pelvic kidney, usually located near the common iliac artery.

Q: First evidence of primordial follicles can be seen in the ovaries at what stage of development?

5th month of intrauterine life. ### Explanation **Correct Answer: A. 5th month of intrauterine life** The development of the female germ cells follows a specific chronological sequence. Primordial germ cells migrate from the yolk sac to the gonadal ridge by the 5th–6th week. These cells undergo rapid mitosis to become **oogonia**. By the **4th to 5th month** of intrauterine life, some oogonia enter the prophase of the first meiotic division and become **primary oocytes**. A **primordial follicle** is formed when a primary oocyte becomes surrounded by a single layer of flattened follicular (granulosa) cells. This process peaks at the **5th month**, marking the first histological evidence of follicles [1]. At this stage, the total number of germ cells reaches its maximum (approximately 7 million) [1]. **Why other options are incorrect:** * **B. 7th month:** By this stage, many oogonia have already become atretic. While primordial follicles are present, they first appeared much earlier (at the 5th month). * **C. Birth:** At birth, no oogonia remain; all germ cells are primary oocytes arrested in the **diplotene stage of prophase I** [1]. The number of follicles has already decreased to about 1–2 million [1]. * **D. Puberty:** This is when follicular maturation (transition to primary, secondary, and antral follicles) begins under the influence of FSH. Only about 400,000 follicles remain at this stage [1]. **High-Yield NEET-PG Pearls:** * **Peak Germ Cell Count:** 7 million at the 5th month of IUL [1]. * **Meiotic Arrest:** Primary oocytes are arrested in the **Diplotene stage** of Prophase I by Oocyte Maturation Inhibitor (OMI) until puberty. * **Meiosis II:** Completed only if **fertilization** occurs. * **Origin:** Granulosa cells are derived from the **coelomic epithelium** of the gonad.

Q: Edwards syndrome is characterized by which chromosomal abnormality?

Trisomy 18. **Explanation:** **Edwards Syndrome** is caused by **Trisomy 18**, a chromosomal condition where there are three copies of chromosome 18 instead of the usual two. This occurs primarily due to meiotic non-disjunction during gametogenesis [1]. It is the second most common autosomal trisomy among live births, following Down syndrome. **Analysis of Options:** * **Trisomy 18 (Correct):** Characterized by severe intellectual disability and multisystem defects. Key features include **clenched fists with overlapping fingers**, rocker-bottom feet, micrognathia (small jaw), and low-set ears. * **Trisomy 21 (Option A):** This is **Down Syndrome**, the most common autosomal trisomy. It is characterized by flat facial profiles, epicanthal folds, and Simian creases [1]. * **Trisomy 13 (Option C):** This is **Patau Syndrome**. It presents with more severe midline defects such as holoprosencephaly, cleft lip/palate, polydactyly, and microphthalmia [2]. * **Cri-du-chat Syndrome (Option D):** This is caused by a **deletion of the short arm of chromosome 5 (5p-)**, not a trisomy. It is noted for a high-pitched, cat-like cry in infants. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Trisomies:** **P**atau (13), **E**dwards (18), **D**own (21) — Think "Puberty at **13**, Election at **18**, Drinking at **21**." * **Edwards Syndrome Hallmark:** Look for "Clenched fists with index finger overlapping the 3rd and 5th finger overlapping the 4th." * **Cardiac defect:** Ventricular Septal Defect (VSD) is the most common cardiac anomaly in Edwards syndrome. * **Prognosis:** Most affected infants die within the first year of life due to respiratory failure or cardiac complications.

Q: Which of the following is NOT a derivative of the paramesonephric duct?

Gartner's duct. ### Explanation The **Paramesonephric duct (Müllerian duct)** is the primordial structure that develops into the female internal reproductive tract in the absence of Anti-Müllerian Hormone (AMH) [1]. **Why Gartner’s Duct is the Correct Answer:** Gartner’s duct is a vestigial remnant of the **Mesonephric duct (Wolffian duct)** in females. While the mesonephric duct regresses in females due to the lack of testosterone, its remnants can persist as Gartner’s cysts along the lateral walls of the vagina. Therefore, it is NOT a derivative of the paramesonephric duct. **Analysis of Other Options:** * **Appendix of testis (Option A):** In males, AMH causes the paramesonephric ducts to degenerate. The only vestigial remnant that persists at the upper pole of the testis is the appendix of the testis. * **Hydatid of Morgagni (Option B):** Also known as the *appendix vesiculosa*, this is a small pedunculated remnant of the cranial end of the paramesonephric duct located near the fimbriated end of the fallopian tube in females [1]. * **Uterus (Option C):** The paramesonephric ducts fuse in the midline to form the uterovaginal canal, which gives rise to the uterus, cervix, and the upper 1/3rd (or 4/5ths) of the vagina [1]. **High-Yield NEET-PG Pearls:** 1. **Paramesonephric Derivatives:** Fallopian tubes, uterus, cervix, upper vagina, and Appendix of testis (male) [1]. 2. **Mesonephric Derivatives:** Epididymis, Vas deferens, Seminal vesicles, Ejaculatory ducts, and Gartner’s duct (female). 3. **Prostatic Utricle:** The male homologue of the uterus/vagina, derived from the paramesonephric duct. 4. **Paradoxical Remnants:** Remember "M" for **M**üllerian = **M**orgagni; "W" for **W**olffian = **G**artner (alphabetically close).

Q: Which of the following is a derivative of the IV pharyngeal pouch?

Superior thyroid glands. The pharyngeal pouches are endodermal outpocketings that give rise to critical structures in the head and neck. Understanding their derivatives is a high-yield topic for NEET-PG. **Why Option C is Correct:** The **Fourth (IV) Pharyngeal Pouch** differentiates into two main components: 1. **Dorsal part:** Develops into the **Superior Parathyroid Glands** (often referred to as Parathyroid IV). 2. **Ventral part:** Forms the **Ultimobranchial body**, which incorporates into the thyroid gland to become **Parafollicular C-cells** (secreting calcitonin). **Analysis of Incorrect Options:** * **A & B (Thymus and Inferior Parathyroid):** These are derivatives of the **Third (III) Pharyngeal Pouch**. Because the thymus migrates further caudally into the mediastinum, it "pulls" the parathyroid III down with it, resulting in them becoming the **Inferior** parathyroid glands. * **D (Auditory tube):** This is derived from the **First (I) Pharyngeal Pouch** (specifically the tubotympanic recess), which also forms the middle ear cavity and the internal layer of the tympanic membrane [1]. **High-Yield Clinical Pearls:** * **DiGeorge Syndrome:** Results from the failure of the 3rd and 4th pouches to develop, leading to thymic hypoplasia (immunodeficiency) and hypoparathyroidism (hypocalcemia). * **Rule of "Inversion":** Remember that the **3rd** pouch forms the **Inferior** parathyroid, while the **4th** pouch forms the **Superior** parathyroid. * **Ectopic Tissue:** Because of the long migration path of the 3rd pouch, ectopic parathyroid or thymic tissue is most commonly found along the descent path in the neck or anterior mediastinum.

Q: The paramesonephric duct develops into which of the following structures?

Uterus. The **Paramesonephric duct (Müllerian duct)** is the primordial structure that develops into the female internal genital tract in the absence of Anti-Müllerian Hormone (AMH). In females, the cranial and horizontal parts of these ducts form the **Fallopian tubes** [1], while the caudal vertical parts fuse in the midline to form the **uterovaginal primordium**, which gives rise to the **uterus** [2], cervix, and the upper 1/3rd of the vagina. **Analysis of Options:** * **A & B (Vas deferens and Seminal vesicle):** These are male internal genital structures derived from the **Mesonephric (Wolffian) duct**. In males, Testosterone promotes the development of these structures, while AMH causes the regression of the Paramesonephric ducts. * **C (Ureter):** The ureter develops from the **Ureteric bud**, which is an outgrowth from the caudal end of the Mesonephric duct. It is part of the urinary system, not the genital duct system. **High-Yield Clinical Pearls for NEET-PG:** * **Remnants:** The vestigial remnant of the Paramesonephric duct in males is the **Appendix testis** and the **Prostatic utricle**. * **Müllerian Agenesis (Mayer-Rokitansky-Küster-Hauser syndrome):** Characterized by the congenital absence of the uterus and upper vagina due to failure of Paramesonephric duct development. * **Fusion Defects:** Failure of the ducts to fuse properly can lead to uterine anomalies such as **Uterus Didelphys** (double uterus) or **Bicornuate uterus** (heart-shaped). * **Rule of Thumb:** Paramesonephric = Female (Müllerian); Mesonephric = Male (Wolffian).

Question 1

Which of the following is an immune-privileged site?

Accepted Answer

Seminiferous tubules

Answer

Area postrema

Answer

Loop of Henle

Answer

Optic nerve

Question 2

Which of the following statements is true of cardiac development?

Accepted Answer

The heart bends into an S-shape because the caudal regions of the endocardial tubes grow faster than the cranial regions

Answer

During formation of the heart loop, a single-tube heart remains suspended by a complete dorsal mesocardium

Answer

The atria are represented by cranial portions of endocardial tubes

Answer

The left and right sides of the heart result directly from side-by-side apposition

Question 3

Defect in any of the following results in renal agenesis, except:

Accepted Answer

Failure of descent of kidney into the lumbar region

Answer

Nephrogenic bud

Answer

Ureteric bud

Answer

Blastema of nephrogenic tissue

Question 4

Trophoblast gives rise to which of the following structures?

Accepted Answer

All of these

Answer

Placenta

Answer

Chorion

Answer

Amnion

Question 5

First evidence of primordial follicles can be seen in the ovaries at what stage of development?

Accepted Answer

5th month of intrauterine life

Answer

7th month of intrauterine life

Answer

Birth

Answer

Puberty

Question 6

Edwards syndrome is characterized by which chromosomal abnormality?

Accepted Answer

Trisomy 18

Answer

Trisomy 21

Answer

Trisomy 13

Answer

Cri-du-chat syndrome (5p deletion)

Question 7

Which of the following is NOT a derivative of the paramesonephric duct?

Accepted Answer

Gartner's duct

Answer

Appendix of testis

Answer

Hydatid of Morgagni

Answer

Uterus

Question 8

The fetus born during the 6th month of intrauterine life will NOT be able to survive due to which of the following reasons?

Accepted Answer

Absence or insufficient amount of surfactant

Answer

Lack of subcutaneous connective tissue

Answer

Lack of co-ordination between the respiratory and nervous system

Answer

Lack of sufficient capillaries

Question 9

Which of the following is a derivative of the IV pharyngeal pouch?

Accepted Answer

Superior thyroid glands

Answer

Thymus glands

Answer

Inferior thyroid glands

Answer

Auditory tube

Question 10

The paramesonephric duct develops into which of the following structures?

Accepted Answer

Uterus

Answer

Vas deferens

Answer

Seminal vesicle

Answer

Ureter

Embryology and Development — MCQs

Embryology and Development — MCQs

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