Embryology and Development Practice Questions

Q: A newborn has multiple congenital defects owing to dysgenesis of the neural crest. Which of the following cells is most likely to be spared?

Motor neurons. ### Explanation The correct answer is **Motor neurons** because they are derived from the **neuroectoderm (neural tube)**, specifically the basal plate, rather than the neural crest. **1. Why Motor Neurons are spared:** Neural crest cells (NCCs) are often called the "fourth germ layer" because they migrate extensively to form various structures. However, the central nervous system (CNS) and the motor components of the peripheral nervous system have different origins. While sensory and autonomic ganglia arise from NCCs, the **somatic motor neurons** (located in the ventral horn of the spinal cord) and **branchial motor neurons** originate from the neuroepithelium of the neural tube. Therefore, dysgenesis of the neural crest will not affect these cells. **2. Analysis of Incorrect Options:** * **Geniculate ganglion cells (A):** All sensory ganglia of cranial nerves (V, VII, IX, and X) and dorsal root ganglia are derived from **neural crest cells** (along with ectodermal placodes). * **Melanocytes (B):** These pigment-producing cells of the skin and uvea are classic derivatives of **neural crest cells**. Their absence leads to conditions like Waardenburg syndrome. * **Parafollicular cells (D):** Also known as C-cells of the thyroid (which secrete calcitonin), these are derived from the **neural crest via the ultimobranchial body. **3. High-Yield NEET-PG Pearls:** * **Mnemonic for NCC derivatives (MOTHER):** **M**elanocytes, **O**dontoblasts, **T**racheal cartilage, **H**eart (conotruncal septum), **E**nteric nervous system/Endocrine (Adrenal medulla), **R**esponses (Sensory/Autonomic ganglia). * **Clinical Correlation:** **DiGeorge Syndrome** and **Treacher Collins Syndrome** are prime examples of "neurocristopathies" (defects in NCC migration/differentiation). * **Key Distinction:** The **Adrenal Medulla** is neural crest-derived (chromaffin cells), while the **Adrenal Cortex** is mesodermal.

Q: The given deformity is due to which of the following developmental anomalies?

Non-fusion of the mandibular processes. ***Non-fusion of the mandibular processes*** - Non-fusion of the **mandibular processes** results in **macrostomia** (lateral or transverse facial cleft), creating an abnormally wide mouth opening. - This developmental anomaly occurs when the **maxillary** and **mandibular processes** fail to fuse properly at the corners of the mouth during embryogenesis. *Non-fusion of the two medial nasal processes* - This anomaly results in **median cleft lip**, characterized by a cleft in the center of the upper lip. - It affects the **philtrum** and central portion of the upper lip, not the lateral mouth opening. *Non-fusion of a medial nasal process and a maxillary process* - This causes **unilateral cleft lip**, the most common type of cleft lip deformity. - It results in a gap in the **upper lip** extending from the lip to the nostril, not affecting mouth width. *Non-fusion of medial and lateral (or alar) processes and a maxillary process* - This anomaly leads to **oblique facial cleft**, a rare condition extending from the mouth toward the eye. - It creates a cleft running from the **upper lip** toward the **lower eyelid**, distinct from lateral mouth enlargement.

Q: Which of the following structures is derived from the surface ectoderm?

Lens of the eye. The development of the eye involves a complex interaction between the surface ectoderm, neuroectoderm, and neural crest cells. **Correct Answer: A. Lens of the eye** The **surface ectoderm** gives rise to structures that form the outer interface of the eye. When the optic vesicle (from the forebrain) contacts the surface ectoderm, it induces the formation of the **lens placode**, which eventually invaginates to form the **lens**. Other surface ectoderm derivatives include the corneal epithelium, lacrimal glands, and the epidermis of the eyelids. **Explanation of Incorrect Options:** * **B. Retina:** The retina develops from the **neuroectoderm** (specifically the optic cup) [1]. The inner layer forms the neural retina, while the outer layer forms the retinal pigment epithelium. * **C. Iris:** The iris develops from the anterior rim of the **optic cup (neuroectoderm)**. Specifically, the sphincter and dilator pupillae muscles are unique as they are among the few muscles in the body derived from the neuroectoderm. * **D. Corneal stroma:** While the corneal epithelium is surface ectoderm, the **corneal stroma** and endothelium are derived from **neural crest cells** (mesenchyme) [2]. **High-Yield NEET-PG Pearls:** * **Neuroectoderm:** Retina, Optic nerve, Iris (including muscles), and Ciliary body epithelium. * **Neural Crest Cells:** Sclera, Corneal stroma, Choroid, and Ciliary muscle. * **Surface Ectoderm:** Lens, Corneal epithelium, and Conjunctiva. * **Clinical Correlation:** Failure of the optic fissure to close results in **Coloboma**, typically affecting the inferior iris.

Q: The given deformity is due to which of the following developmental anomalies?

Non-fusion of the mandibular processes. ***Non-fusion of the mandibular processes*** - **Macrostomia** results from failure of fusion between the **mandibular processes** during the 6th week of embryonic development. - This anomaly causes an abnormally **wide mouth** extending laterally beyond the normal commissures. *Non-fusion of the two medial nasal processes* - This would result in a **median cleft lip**, creating a central defect in the upper lip. - The deformity would be located in the **midline** of the face, not affecting mouth width. *Non-fusion of a medial nasal process and a maxillary process* - This causes **unilateral cleft lip**, typically involving the upper lip and potentially the alveolar ridge. - Results in a **vertical cleft** on one side of the upper lip, not horizontal mouth widening. *Non-fusion of medial and lateral (or alar) processes and a maxillary process* - This would produce an **oblique facial cleft**, extending from the mouth toward the eye. - Creates a **diagonal cleft** across the face, distinct from the horizontal mouth extension seen in macrostomia.

Q: Defect in any of the following may result in renal agenesis except?

Failure of descent of nephrogenic tissue of lumbar area. Renal development depends on a complex reciprocal induction between two key embryological structures: the **Ureteric Bud** and the **Metanephric Blastema** (nephrogenic tissue). **Why Option D is the correct answer:** Renal agenesis is a failure of the kidney to form. The kidneys actually develop in the **sacral/pelvic region** and subsequently **ascend** to the lumbar area. A failure of descent is embryologically impossible; rather, a failure of *ascent* results in an **Ectopic Kidney** (often a Pelvic Kidney), not agenesis. Since the kidney has already formed but is simply in the wrong location, it is not considered agenesis. **Analysis of Incorrect Options:** * **A & C (Nephrogenic bud/Blastoma):** The metanephric blastema (nephrogenic tissue) forms the nephrons (excretory part). If this tissue is absent or defective, no kidney tissue can develop. * **B (Ureteric bud):** The ureteric bud (a diverticulum of the Wolffian duct) must penetrate the metanephric blastema to induce it to form the kidney [1]. If the ureteric bud fails to develop or reach the blastema, the result is **Renal Agenesis**. **NEET-PG High-Yield Pearls:** * **Reciprocal Induction:** Ureteric bud (forms collecting system: ureter, pelvis, calyces, collecting ducts) $\leftrightarrow$ Metanephric blastema (forms excretory system: Bowman’s capsule to DCT). * **Potter’s Sequence:** Bilateral renal agenesis leads to oligohydramnios, pulmonary hypoplasia, and characteristic flattened facies [2]. * **Unilateral Agenesis:** Often asymptomatic; usually associated with a single umbilical artery. * **Blood Supply:** As the kidney ascends, it receives new arterial branches from the aorta at higher levels; failure of lower vessels to degenerate results in **Accessory Renal Arteries**.

Q: The medial umbilical ligament is a remnant of which fetal structure?

Distal part of the umbilical artery. ### Explanation The correct answer is **A. Distal part of the umbilical artery.** **1. Why the Correct Answer is Right:** During fetal life, the umbilical arteries carry deoxygenated blood from the fetus to the placenta. After birth, when the umbilical cord is clamped, these arteries undergo functional closure [3]. The **distal portion** of each umbilical artery obliterates and fibroses to form the **medial umbilical ligament** (sometimes referred to as lateral umbilical ligaments in specific obstetrics texts), which is found on the inner surface of the anterior abdominal wall, covered by the medial umbilical fold [3]. **2. Analysis of Incorrect Options:** * **B. Distal part of the umbilical vein:** The umbilical vein (specifically the left one) obliterates to form the **Ligamentum teres hepatis** (Round ligament of the liver), which runs in the free edge of the falciform ligament [2], [3]. * **C. Proximal part of the umbilical artery:** The proximal portion of the umbilical artery remains **patent** after birth and gives rise to the **superior vesical arteries**, which supply the upper part of the urinary bladder [3]. * **D. Urachus:** The urachus is a remnant of the allantois [1]. It obliterates to form the **median umbilical ligament** (singular, in the midline), not the medial umbilical ligament. **3. High-Yield Clinical Pearls for NEET-PG:** * **Median vs. Medial:** Remember the "N" for **Median** is in the middle (Urachus), while **Medial** (Umbilical Artery) is lateral to it. * **Lateral Umbilical Fold:** This contains the **inferior epigastric vessels** (not a fetal remnant). This is a crucial landmark for distinguishing direct from indirect inguinal hernias. * **Patent Urachus:** Failure of the urachus to obliterate leads to urine leaking from the umbilicus. * **Patent Vitellointestinal Duct:** Leads to fecal discharge from the umbilicus [1].

Q: What is the most common congenital anomaly of the upper renal tract?

Duplication of renal pelvis. **Explanation:** **Correct Answer: A. Duplication of renal pelvis** The most common congenital anomaly of the upper urinary tract is a **duplicated collecting system**. Among the variations of this anomaly, **duplication of the renal pelvis** (bifid pelvis) is the most frequent. It occurs when the ureteric bud bifurcates before it enters the metanephros. This condition is often asymptomatic and discovered incidentally during imaging. **Analysis of Options:** * **B. Duplication of ureter:** While common, a complete duplication (two separate ureters entering the bladder) is less frequent than a simple duplication of the renal pelvis or a partial (Y-shaped) ureter. * **C. Ectopic ureteric orifice:** This is a relatively rare anomaly where the ureter opens at a site other than the posterolateral angle of the bladder trigone. It is more common in females and often associated with a duplicated system, but it is not the most common overall. * **D. Congenital megaureter:** This refers to an intrinsic functional or organic obstruction at the vesicoureteric junction leading to dilatation. It is a significant cause of hydroureteronephrosis in children but is less common than pelvic duplication. **Clinical Pearls for NEET-PG:** * **Weigert-Meyer Law:** In complete ureteric duplication, the ureter from the **upper pole** opens **medially and inferiorly** to the normal insertion and is prone to **obstruction (ureterocele)**. The ureter from the **lower pole** opens laterally and superiorly and is prone to **vesicoureteric reflux (VUR)**. * **Most common renal fusion anomaly:** Horseshoe kidney. * **Most common cause of bladder outlet obstruction in male infants:** Posterior Urethral Valves (PUV). * **Most common site of urinary obstruction in children:** Pelviureteric junction (PUJ) obstruction.

Q: The biceps brachii muscle develops from which of the following embryological structures?

Anterior condensation. Explanation: The development of limb musculature begins during the 5th week of gestation when myogenic precursor cells migrate from the **somites** (dermomyotome) into the limb buds. These cells organize into two primary masses: the **Anterior (Ventral) condensation** and the **Posterior (Dorsal) condensation**. 1. **Why Anterior Condensation is correct:** The anterior condensation gives rise to the **flexor and pronator** muscles of the upper limb and the **flexor and adductor** muscles of the lower limb. Since the **Biceps Brachii** is a primary flexor of the elbow and supinator of the forearm, it originates from the anterior condensation. 2. **Why Posterior Condensation is incorrect:** This mass gives rise to the **extensor and supinator** muscles of the upper limb (e.g., Triceps brachii, Brachioradialis) and the **extensor and abductor** muscles of the lower limb. 3. **Why Epimere and Hypomere are incorrect:** These terms refer to the division of the **myotome** in the trunk, not the limbs. * **Epimere (Dorsal):** Develops into the intrinsic muscles of the back (Erector spinae), innervated by dorsal rami. * **Hypomere (Ventral):** Develops into the muscles of the thoracic and abdominal walls (e.g., Intercostals, Rectus abdominis), innervated by ventral rami. **High-Yield Clinical Pearls for NEET-PG:** * **Innervation Rule:** Muscles from the anterior condensation are supplied by the **anterior divisions** of the brachial plexus (Musculocutaneous, Median, Ulnar nerves). * **Lower Limb Exception:** While the Biceps Brachii (Upper Limb) is anterior, the **Biceps Femoris** (Lower Limb) is unique: its long head is from the anterior condensation (Tibial N.), while the short head is from the posterior condensation (Common Peroneal N.). * **Origin:** All limb muscles are derived from **paraxial mesoderm** (somites), whereas the limb skeleton is derived from **lateral plate mesoderm** (somatic layer).

Q: Which gene is primarily responsible for eye morphogenesis?

Pax-6. **Explanation:** **Pax-6: The Master Control Gene** Pax-6 is recognized as the **"master control gene"** for eye development. It is a transcription factor expressed in the anterior neural ridge of the neural plate. Its primary role is to initiate the formation of the optic cup and lens vesicle. Without Pax-6, the complex cascade of signaling required for eye morphogenesis fails to occur. **Analysis of Options:** * **Pax-6 (Correct):** It is essential for the development of the entire eye. Mutations in Pax-6 are classically associated with **Aniridia** (absence of iris) and Peter’s anomaly in humans. * **BMP-4 (Bone Morphogenetic Protein 4):** While involved in various induction processes, it primarily functions in dorso-ventral patterning and limb development. In the eye, it plays a secondary role in optic cup differentiation but is not the primary morphogenetic trigger. * **HOX-D13:** Mutations in this gene lead to **Synpolydactyly** (fusion and extra digits). It is involved in limb morphogenesis, specifically the fingers and toes [1]. * **HOX-A13:** Mutations in this gene cause **Hand-Foot-Genital Syndrome**. It governs the development of the distal limbs and the urinary/reproductive tracts. **High-Yield Clinical Pearls for NEET-PG:** * **Sonic Hedgehog (SHH):** This gene is responsible for separating the single eye field into two. **Loss of SHH** leads to **Cyclopia** (a single midline eye) and holoprosencephaly. * **Coloboma:** Results from the failure of the **choroid fissure** to close during the 7th week of development. * **Lens Origin:** The lens develops from the **surface ectoderm**, while the retina and optic nerve develop from the **neuroectoderm**.

Question 1

A newborn has multiple congenital defects owing to dysgenesis of the neural crest. Which of the following cells is most likely to be spared?

Accepted Answer

Motor neurons

Answer

Geniculate ganglion cells

Answer

Melanocytes

Answer

Parafollicular cells

Question 2

The bladder develops from which germ layer?

Accepted Answer

Endoderm

Answer

Ectoderm

Answer

Mesoderm

Answer

Neural crest cell

Question 3

The given deformity is due to which of the following developmental anomalies?

Accepted Answer

Non-fusion of the mandibular processes

Answer

Non-fusion of the two medial nasal processes

Answer

Non-fusion of a medial nasal process and a maxillary process

Answer

Non-fusion of medial and lateral (or alar) processes and a maxillary process

Question 4

Which of the following structures is derived from the surface ectoderm?

Accepted Answer

Lens of the eye

Answer

Retina

Answer

Iris

Answer

Corneal stroma

Question 5

The given deformity is due to which of the following developmental anomalies?

Accepted Answer

Non-fusion of the mandibular processes

Answer

Non-fusion of the two medial nasal processes

Answer

Non-fusion of a medial nasal process and a maxillary process

Answer

Non-fusion of medial and lateral (or alar) processes and a maxillary process

Question 6

Defect in any of the following may result in renal agenesis except?

Accepted Answer

Failure of descent of nephrogenic tissue of lumbar area

Answer

Nephrogenic bud

Answer

Ureteric bud

Answer

Blastoma of nephrogenic tissue

Question 7

The medial umbilical ligament is a remnant of which fetal structure?

Accepted Answer

Distal part of the umbilical artery

Answer

Distal part of the umbilical vein

Answer

Proximal part of the umbilical artery

Answer

Urachus

Question 8

What is the most common congenital anomaly of the upper renal tract?

Accepted Answer

Duplication of renal pelvis

Answer

Duplication of ureter

Answer

Ectopic ureteric orifice

Answer

Congenital megaureter

Question 9

The biceps brachii muscle develops from which of the following embryological structures?

Accepted Answer

Anterior condensation

Answer

Hypomere

Answer

Epimere

Answer

Posterior condensation

Question 10

Which gene is primarily responsible for eye morphogenesis?

Accepted Answer

Pax-6

Answer

BMP-4

Answer

HOX-D13

Answer

HOX-A13

Embryology and Development — MCQs

Embryology and Development — MCQs

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