Embryology and Development Practice Questions

Q: Meckel's diverticulum is classified as which of the following?

A true diverticulum. **Explanation:** **Meckel’s Diverticulum** is the most common congenital anomaly of the gastrointestinal tract. It results from the incomplete obliteration of the **vitellointestinal duct** (omphalomesenteric duct) during the 5th–8th week of gestation. 1. **Why Option B is correct:** It is a **true diverticulum** because it contains **all layers of the intestinal wall** (mucosa, submucosa, and muscularis propria). In contrast, "false" diverticula (like Zenker’s or colonic diverticula) only involve the herniation of mucosa and submucosa through the muscular layer. 2. **Why other options are incorrect:** * **Option A:** It is **congenital**, not acquired. Acquired diverticula usually develop later in life due to increased intraluminal pressure. * **Option C:** It is located in the **ileum**, specifically within 2 feet (60 cm) of the ileocecal valve, not the jejunum. * **Option D:** It always occurs on the **antimesenteric border** of the ileum. This is a crucial surgical landmark to distinguish it from duplication cysts, which occur on the mesenteric side. **High-Yield Clinical Pearls (Rule of 2s):** * **2%** of the population is affected. * Located **2 feet** proximal to the ileocecal valve. * Approximately **2 inches** in length. * Contains **2 types of ectopic tissue**: Gastric (most common, causes bleeding) and Pancreatic. * Most common presentation in children is **painless lower GI bleeding** (due to acid secretion from ectopic gastric mucosa causing ileal ulcers). * Most common presentation in adults is **intestinal obstruction**. * **Investigation of choice:** Meckel’s Scan (Technetium-99m pertechnetate scan) which labels ectopic gastric mucosa.

Q: By which week of gestation is the fetal choroidal fissure closed?

6th week. ### Explanation The development of the eye begins around the 4th week of gestation. The **optic vesicle** invaginates to form a double-layered **optic cup**. This invagination extends along the ventral surface of the optic cup and the optic stalk, forming a groove known as the **choroidal (or optic) fissure**. **Why 6th week is correct:** The primary purpose of the choroidal fissure is to allow the **hyaloid artery** to reach the inner chamber of the eye. Under normal developmental conditions, the margins of this fissure grow toward each other and fuse, surrounding the hyaloid vessels. This fusion begins in the center and spreads anteriorly and posteriorly, completing by the **6th week** of gestation. **Analysis of Incorrect Options:** * **3rd week:** At this stage, the embryo is undergoing gastrulation; the optic primordia (optic grooves) only begin to appear at the end of the 3rd week/start of the 4th week. * **4th week:** This is when the optic vesicle first appears and the choroidal fissure begins to form, not close. * **8th week:** By this time, the fissure should have been closed for two weeks. Delay or failure in closure by this stage results in permanent structural defects. **Clinical Pearls for NEET-PG:** * **Coloboma:** Failure of the choroidal fissure to close results in a Coloboma. It typically occurs in the **inferonasal quadrant** and can affect the iris, ciliary body, retina, or optic nerve. * **Hyaloid Artery:** The distal part of this artery eventually degenerates, while the proximal part persists as the **central artery of the retina**. * **Pax2 Gene:** Mutations in the *PAX2* gene are often associated with optic fissure closure defects (Renal-coloboma syndrome).

Q: Bicornuate uterus is due to:

Incomplete fusion of the paramesonephric duct. Explanation: The development of the female reproductive tract primarily involves the **Paramesonephric (Müllerian) ducts**. In a normal embryo, these ducts undergo a three-stage process: elongation, **midline fusion**, and canalization (septal resorption). [1] **1. Why Option B is Correct:** The uterus, cervix, and upper 1/3rd of the vagina are formed by the fusion of the two paramesonephric ducts [1]. A **Bicornuate Uterus** (heart-shaped uterus) occurs specifically due to the **partial failure of fusion** of the paramesonephric ducts at the superior aspect [2]. This results in two separate uterine horns entering a single cervix. **2. Why Other Options are Wrong:** * **Option A:** Incomplete fusion of the uterine cavity is a vague description. The pathology lies in the fusion of the ducts themselves, not just the internal cavity. * **Option C:** The **Mesonephric (Wolffian) ducts** regress in females due to the absence of testosterone. They contribute to the male reproductive system (epididymis, vas deferens). In females, remnants may persist as Gartner’s cysts. * **Option D:** The vagina has a dual origin. The upper 1/3rd comes from paramesonephric ducts, while the lower 2/3rd comes from the **urogenital sinus** (sino-vaginal bulbs) [1]. Incomplete formation leads to vaginal atresia or agenesis, not a bicornuate uterus. **High-Yield Clinical Pearls for NEET-PG:** * **Septate Uterus:** Failure of **resorption** of the midline septum (most common Mullerian anomaly) [2]. * **Uterus Didelphys:** Complete failure of fusion of paramesonephric ducts (double uterus, double cervix) [3]. * **Mayer-Rokitansky-Küster-Hauser (MRKH) Syndrome:** Müllerian agenesis (absent uterus and upper vagina). * **Renal Anomalies:** Always screen the urinary tract (via ultrasound) in patients with uterine anomalies, as both systems develop from the intermediate mesoderm simultaneously.

Q: On what day after fertilization do syncytiotrophoblasts and cytotrophoblasts differentiate?

8 days. The differentiation of the trophoblast is a hallmark of the **second week of development**, often referred to as the **"Week of Twos."** Around **Day 8** (shortly after implantation begins), the trophoblast differentiates into two distinct layers [1]: 1. **Cytotrophoblast:** The inner layer of mononucleated cells with distinct cell boundaries (the "cellular" layer). 2. **Syncytiotrophoblast:** The outer, multinucleated zone without distinct cell boundaries that invades the uterine endometrium [1]. **Analysis of Options:** * **Day 6 (Option A):** This is when the blastocyst typically begins to **attach** to the endometrial epithelium. Differentiation into two distinct layers is not yet complete. * **Day 8 (Option B - Correct):** By this day, the blastocyst is partially embedded, and the trophoblast has clearly differentiated into the cyto- and syncytiotrophoblast [1]. Simultaneously, the embryoblast divides into the epiblast and hypoblast [1]. * **Day 10 (Option C):** By this stage, the blastocyst is more deeply embedded, and fibrin coagula close the penetration defect in the surface epithelium. * **Day 12 (Option D):** This period is characterized by the formation of **extraembryonic mesoderm** and the development of lacunar networks within the syncytiotrophoblast to establish uteroplacental circulation [1]. **High-Yield NEET-PG Pearls:** * **Rule of Twos:** 2 trophoblast layers (Cyto/Syncytio), 2 embryoblast layers (Epi/Hypoblast), and 2 cavities (Amniotic/Yolk sac) all form in the 2nd week [1]. * **hCG Production:** The **syncytiotrophoblast** is responsible for secreting Human Chorionic Gonadotropin (hCG), which maintains the corpus luteum [1]. * **Mitosis:** Only cytotrophoblast cells undergo mitosis; they then migrate into the syncytiotrophoblast, where they lose their cell membranes [1].

Q: The pars intermedia of the hypophysis cerebri is derived from which embryonic germ layer?

Oral ectoderm. The pituitary gland (hypophysis cerebri) has a dual embryological origin, arising from two different sources of **ectoderm**. **Why Oral Ectoderm is Correct:** The pituitary gland develops from two distinct buds. The **adenohypophysis** (anterior lobe) develops from an upward growth of the **oral ectoderm** (primitive mouth cavity) known as **Rathke’s pouch**. This pouch eventually pinches off from the stomodeum and differentiates into three parts: 1. **Pars distalis:** The main anterior part. 2. **Pars tuberalis:** The part wrapping around the infundibulum. 3. **Pars intermedia:** The thin layer between the anterior and posterior lobes. Since the pars intermedia is a derivative of Rathke’s pouch, its origin is oral ectoderm [1]. **Why Incorrect Options are Wrong:** * **Endoderm:** Does not contribute to the formation of the pituitary gland. * **Mesoderm:** Forms the connective tissue and vascular supply of the gland, but not the functional parenchyma or the pars intermedia. * **Neuroectoderm:** This gives rise to the **neurohypophysis** (posterior lobe) via a downward growth from the floor of the diencephalon (the infundibulum) [1]. It forms the pars nervosa, the infundibular stem, and the median eminence [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Craniopharyngioma:** A tumor arising from the remnants of **Rathke’s pouch**. It is the most common suprasellar tumor in children and often shows calcification on imaging. * **Pharyngeal Pituitary:** Occasionally, a small portion of Rathke’s pouch persists in the roof of the pharynx. * **Empty Sella Syndrome:** A condition where the subarachnoid space extends into the sella turcica, flattening the pituitary gland.

Q: Failure of closure of the posterior neuropore causes what condition?

Spina bifida. ### Explanation The development of the central nervous system begins with **neurulation**, where the neural plate folds to form the neural tube. This tube remains open at both ends via the cranial (anterior) and caudal (posterior) neuropores. **1. Why Spina Bifida is Correct:** The **posterior (caudal) neuropore** normally closes around **Day 27** of embryonic development. Failure of this closure results in **Spina Bifida**, a group of neural tube defects (NTDs) characterized by an incomplete closure of the vertebral column and spinal cord [1], [3]. This can range from *Spina Bifida Occulta* (mildest) to *Meningomyelocele* (most severe) [2]. **2. Analysis of Incorrect Options:** * **Anencephaly:** This results from the failure of the **anterior (cranial) neuropore** to close (around Day 25) [3]. It leads to the absence of a major portion of the brain and skull. * **Gastroschisis & Omphalocele:** These are **ventral body wall defects** related to the abdominal cavity, not the neural tube. **3. NEET-PG High-Yield Pearls:** * **Folic Acid:** Supplementation (400 mcg/day) pre-conception and during early pregnancy significantly reduces the risk of NTDs. * **Biomarkers:** Elevated **Alpha-fetoprotein (AFP)** in maternal serum and amniotic fluid [3], along with increased **Acetylcholinesterase** in amniotic fluid, are diagnostic markers for open NTDs. * **Closure Sequence:** Anterior neuropore closes first (Day 25), followed by the posterior neuropore (Day 27). Remember: "Head before Tail."

Q: Hemivertebra is a defect of which part of the vertebra?

Body. **Explanation:** **Hemivertebra** is a congenital spinal anomaly where only one side of the vertebral body develops. This occurs due to the **failure of one of the two lateral chondrification centers** of the vertebral body to form or fuse during embryonic development (around the 6th week of gestation). * **Why Option A is Correct:** The vertebral body (centrum) develops from two primary ossification centers. If one center fails to develop, only half of the body forms, resulting in a wedge-shaped vertebra. This is the most common cause of congenital scoliosis, as the asymmetrical growth leads to lateral curvature of the spine. * **Why Other Options are Incorrect:** * **Options B & C (Transverse process and Spine):** These are parts of the vertebral arch. While they may be secondary victims of the deformity, their primary development is not the cause of a hemivertebra. * **Option D (Posterior vertebral arches):** Defects in the fusion of the posterior arches lead to **Spina Bifida**, not hemivertebra. The arches develop from separate primary ossification centers located in each half of the neural arch. **High-Yield Clinical Pearls for NEET-PG:** 1. **Congenital Scoliosis:** Hemivertebra is the most frequent cause of structural congenital scoliosis. 2. **VACTERL Association:** Hemivertebrae are often associated with other anomalies (Vertebral, Anal, Cardiac, Tracheo-Esophageal, Renal, and Limb). 3. **Butterfly Vertebra:** Occurs when both lateral chondrification centers fail to fuse in the midline, leaving a central cleft. 4. **Ossification Centers:** A typical vertebra has **3 primary centers** (1 for the body, 2 for the arches) and **5 secondary centers** (appearing at puberty).

Question 1

A double aortic arch is due to persistence and continued patency of which segment?

Accepted Answer

Right dorsal aorta between the right seventh intersegmental artery and its junction with the left dorsal aorta

Answer

Right dorsal aorta between the right sixth intersegmental artery and its junction with the left dorsal aorta

Answer

Left dorsal aorta between the right seventh intersegmental artery and its junction with the left dorsal aorta

Answer

Left dorsal aorta between the right sixth intersegmental artery and its junction with the left dorsal aorta

Question 2

In a fetus, in which location is the highest oxygen concentration found?

Accepted Answer

Inferior vena cava (IVC)

Answer

Superior vena cava (SVC)

Answer

Right ventricle

Answer

Aorta (ascending)

Question 3

Tertiary stem villi consist of which of the following structures?

Accepted Answer

Central fetal blood vessels surrounded by mesoderm and trophoblast.

Answer

A central core of cytotrophoblast covered with synctiotrophoblast.

Answer

A central core of extra-embryonic mesoderm covered by central cytotrophoblast and peripheral synctiotrophoblast.

Answer

Central maternal blood vessels surrounded by mesoderm and trophoblast.

Question 4

Meckel's diverticulum is classified as which of the following?

Accepted Answer

A true diverticulum

Answer

An acquired diverticulum

Answer

A diverticulum seen in the jejunum

Answer

A diverticulum seen on the mesenteric side

Question 5

By which week of gestation is the fetal choroidal fissure closed?

Accepted Answer

6th week

Answer

3rd week

Answer

4th week

Answer

8th week

Question 6

Bicornuate uterus is due to:

Accepted Answer

Incomplete fusion of the paramesonephric duct

Answer

Incomplete fusion of the uterine cavity

Answer

Incomplete fusion of the mesonephric duct

Answer

Incomplete formation of the vagina

Question 7

On what day after fertilization do syncytiotrophoblasts and cytotrophoblasts differentiate?

Accepted Answer

8 days

Answer

6 days

Answer

10 days

Answer

12 days

Question 8

The pars intermedia of the hypophysis cerebri is derived from which embryonic germ layer?

Accepted Answer

Oral ectoderm

Answer

Endoderm

Answer

Mesoderm

Answer

Neuroectoderm

Question 9

Failure of closure of the posterior neuropore causes what condition?

Accepted Answer

Spina bifida

Answer

Anencephaly

Answer

Gastroschisis

Answer

Omphalocele

Question 10

Hemivertebra is a defect of which part of the vertebra?

Accepted Answer

Body

Answer

Transverse process

Answer

Spine

Answer

Posterior vertebral arches

Embryology and Development — MCQs

Embryology and Development — MCQs

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