Embryology and Development Practice Questions

Q: Which of the following statements with regard to Meckel's Diverticulum are correct? 1. It represents a persistent remnant of the vitellointestinal duct. 2. It is a true diverticulum of gastrointestinal tract. 3. It is most commonly found on anti-mesenteric border of ileum. 4. Heterotopic mucosa is present in 50-60% of patients. Select the correct answer using the code given below:

1, 2 and 3. ***Option: 1, 2 and 3 (Correct Answer)*** - **Statement 1 is correct:** Meckel's diverticulum is a **congenital anomaly** resulting from incomplete obliteration of the **vitellointestinal (vitelline) duct**, which connects the midgut to the yolk sac during embryonic development [1]. - **Statement 2 is correct:** It is a **true diverticulum** because it contains all three layers of the intestinal wall: mucosa, submucosa, and muscularis propria (unlike false diverticula which only contain mucosa and submucosa). - **Statement 3 is correct:** It arises from the **anti-mesenteric border of the ileum**, typically within 60-100 cm proximal to the ileocecal valve [1]. - **Statement 4 is incorrect:** Heterotopic mucosa (most commonly gastric mucosa, followed by pancreatic tissue) is present in approximately **20-30% of all Meckel's diverticula**. The 50-60% figure applies specifically to **symptomatic cases**, not all patients with the condition [1]. *Option: 1, 3 and 4* - While statements 1 and 3 are correct, statement 4 overstates the prevalence of heterotopic mucosa in the general population with Meckel's diverticulum [1]. - Additionally, this option excludes statement 2, which is definitively correct and represents an essential characteristic of Meckel's as a true diverticulum. *Option: 1, 2 and 4* - Statements 1 and 2 are correct, but statement 4's percentage for heterotopic mucosa (50-60%) is too high for the overall population [1]. - The actual prevalence of heterotopic mucosa is **20-30% in all cases**, though it is found in the majority of symptomatic presentations. *Option: 1 and 3* - While statements 1 and 3 are correct, this option incorrectly excludes statement 2. - Statement 2 is unequivocally correct: Meckel's is a **true diverticulum** with all intestinal wall layers, which distinguishes it from false diverticula.

Q: A meningomyelocele is most commonly situated in the

Lumbosacral spine. ***Lumbosacral spine*** - The **lumbosacral region** (L5-S1) is the most frequent anatomical site for meningomyelocele due to the timing of neural tube closure. - This area is the last portion of the **neural tube** to close, making it more susceptible to defects if closure is incomplete [1]. *Thoracic spine* - While meningomyeloceles can occur in the thoracic region, it is far less common than in the lumbosacral area [1]. - Defects in the thoracic spine are usually associated with a higher level of neurological impairment [1]. *Dorsolumbar spine* - This term encompasses the lower thoracic and upper lumbar regions; while possible, it is not the most common singular site. - The lumbosacral region has a higher prevalence of meningomyelocele formation. *Cervical spine* - Meningoceles and meningomyeloceles in the cervical spine are much rarer. - These defects often present with different neurological findings compared to lumbosacral lesions, such as upper limb weakness.

Q: Monoamniotic monochorionic twins develop when the division of cell mass occurs

after 8th day of fertilization. ***after 8th day of fertilization*** - If division occurs **after the 8th day** post-fertilization, the twins will share both the **amnion** and **chorion**, leading to monoamniotic monochorionic twins. - This late division stage means the **amniotic cavity** has already formed for both embryos, and they share the same amniotic fluid and placenta. *after 2 weeks of development of embryonic disc* - Division this late (after 2 weeks, or day 14) would be extremely rare and usually results in **conjoined twins**, as the embryonic disc has already significantly developed. - At this stage, the primitive streak has formed, and further division would likely involve shared organs or structures. *within 72 hours after fertilization* - Division within the first 72 hours (days 0-3) typically results in **dichorionic diamniotic twins**, meaning each twin has its own placenta and amniotic sac. - This early division occurs before the formation of the inner cell mass and trophoblast differentiate into distinct structures. *between 4th and 8th day of fertilization* - Division between days 4 and 8 most commonly leads to **monochorionic diamniotic twins**, where the twins share a placenta but have separate amniotic sacs. - This timing corresponds to the formation of a common chorion before the development of separate amniotic cavities.

Q: The lungs are derived from an out-pouching of the primitive foregut during which period of intrauterine life?

4th week. ***4th week*** - The **respiratory diverticulum (lung bud)** appears as a ventral out-pouching from the **primitive foregut** at approximately **26-28 days** of development, which falls in the **4th week** of intrauterine life [1]. - This marks the beginning of the respiratory system's development, initiating the formation of the **larynx**, **trachea**, **bronchi**, and **lungs** [1]. - The lung bud forms from the foregut endoderm and subsequently divides into the **right and left bronchial buds**. *3rd week* - During the third week, **gastrulation** occurs with the formation of the three germ layers (ectoderm, mesoderm, endoderm). - The **primitive gut tube** begins to form toward the end of the third week through **lateral and cranio-caudal folding**, but the respiratory diverticulum has not yet appeared. - The lung bud out-pouching occurs later, around day 26-28 of the fourth week. *5th week* - By the fifth week, the **laryngotracheal tube** has separated from the foregut via the **tracheoesophageal septum**. - The main **bronchi** continue to elongate and branch into **secondary (lobar) bronchi**. - The initial formation of the lung bud precedes this developmental stage. *6th week* - By the sixth week, the **bronchial tree** undergoes further branching with the formation of **tertiary (segmental) bronchi**. - The **pseudoglandular stage** of lung development is underway, with continued airway differentiation. - This represents a later stage of respiratory development, well after the initial lung bud formation [1].

Q: Regarding “conjoined twins”, which of the following statements is/are true? 1. These are always monozygotic 2. These result when division occurs before the embryonic disc is formed 3. Most common variety is thoracopagus Select the correct answer using the code given below:

1 and 3 only. ***1 and 3 only*** - **Identical (monozygotic)** twins are always conjoined because they develop from a single fertilized egg that imperfectly separates. - **Incomplete division** of the embryonic disc after 13 days from fertilization causes conjoined twins [1]. **Thoracopagus** is the most common type, where twins are joined at the chest [1, 2]. *1 and 2 only* - Conjoined twins are indeed **monozygotic**, but the timing of division is typically *after* the embryonic disc is formed, not before [1]. - Division *before* the embryonic disc forms would usually lead to separate monozygotic twins [1]. *2 and 3 only* - While **thoracopagus** is the most common variety [2], statement 2 regarding the timing of division is incorrect. - Conjoined twins are a result of incomplete separation *after* the formation of the embryonic disc, typically around 13-15 days post-fertilization [1]. *1, 2 and 3* - This option incorrectly states that division occurs *before* the embryonic disc is formed. - The formation of conjoined twins results from an *incomplete* splitting of the **monozygotic embryo** *after* the embryonic disc has already begun to differentiate [1].

Q: The umbilical cord normally contains:

Two arteries and one vein. ***Two arteries and one vein*** - The umbilical cord typically contains **two umbilical arteries** [1] that carry deoxygenated blood and waste products from the fetus to the placenta. - It also contains **one umbilical vein** [2, 3] that carries oxygenated, nutrient-rich blood from the placenta to the fetus. - This is the **normal anatomical configuration** of the umbilical cord. *One artery and two veins* - This configuration is **incorrect** as there is only **one umbilical vein** [2] in the normal umbilical cord, not two. - The presence of a single artery (single umbilical artery - SUA) is a recognized anomaly associated with certain fetal abnormalities, but even in SUA, there is only one vein. *One artery and one vein* - This arrangement is **incorrect** as the normal umbilical cord contains **two arteries**, not one [1]. - Single umbilical artery (SUA) is the most common umbilical cord anomaly, occurring in about 1% of pregnancies, but this is still an abnormal finding. *Two arteries and two veins* - This statement is **incorrect** because the normal umbilical cord contains only **one umbilical vein**, not two. - The presence of two veins would be a rare anomaly and is not part of normal umbilical cord anatomy.

Q: The external opening of branchial fistula is present in :

Lower third of the neck. ***Lower third of the neck*** - The external opening of a branchial fistula is typically found in the **lower third of the anterolateral neck**, anterior to the sternocleidomastoid muscle [1]. - This location corresponds to the embryological remnants of the second branchial cleft failing to close completely. *Middle third of the neck* - While other branchial anomalies might present in the middle third, the classic external opening of a **branchial fistula** is usually lower [1]. - Cysts (branchial cleft cysts) are more commonly found in the middle third [1]. *Upper third of the neck* - Anomalies in the upper third of the neck are less common for an external branchial fistula opening. - This region is more associated with anomalies of the first branchial cleft [1]. *Suprasternal notch* - The suprasternal notch is located at the base of the neck, and while cysts can occur in this area (e.g., cervicomediastinal thymic cysts), it is not the typical site for a **branchial fistula** opening. - This location is often associated with abnormalities of thyroid development or other midline defects.

Q: Defective fusion of the Mullerian ducts may give rise to which of the following?

Uterus bicornis unicollis. ***Uterus bicornis unicollis*** - This condition results from the **incomplete fusion** of the two Müllerian ducts, leading to a uterus with a **septum** or two distinct uterine cavities but a single cervix and vagina. - The Müllerian ducts are embryological structures that develop into the **female reproductive tract**, including the uterus, fallopian tubes, cervix, and upper two-thirds of the vagina. *Imperforate anus* - This congenital condition is due to the **failure of the anal membrane to rupture** during development, not related to Müllerian duct fusion. - It affects the **gastrointestinal tract** and is not derived from Müllerian structures. *Absence of the ovaries* - The **ovaries** develop from the **gonadal ridges** and are distinct from the Müllerian ducts; therefore, their absence is not due to defective Müllerian fusion. - Conditions like **gonadal dysgenesis** can lead to absent or streak ovaries. *Imperforate hymen* - An imperforate hymen results from the failure of the **hymen to canalize** during fetal development, leading to an obstruction of the vaginal introitus. - The hymen is formed from the **urogenital sinus**, which is embryologically distinct from the Müllerian ducts.

Q: Implantation of a fertilised ovum occurs on which day following fertilisation?

Day 6. ***Day 6*** * Fertilization occurs in the **ampulla** of the fallopian tube, and the zygote undergoes cleavage as it travels towards the uterus. * By day 5-6, the embryo develops into a **blastocyst** with an outer trophoblast layer and inner cell mass. * **Implantation begins on day 6-7** post-fertilization when the blastocyst attaches to the endometrium, making day 6 the correct answer for when implantation occurs. * The process continues and is complete by day 10-12, but the initial attachment (implantation) starts on day 6. *Incorrect: Day 14* * Day 14 marks the time of **ovulation** in a typical 28-day menstrual cycle, not implantation. * By day 14 post-fertilization, the embryo would have been implanted for approximately one week. *Incorrect: Day 20* * Implantation occurs much earlier, around day 6-12 post-fertilization. * By day 20 post-fertilization, the implanted embryo would be well into **gastrulation and organogenesis**. *Incorrect: Day 10* * While the implantation process may continue until day 10-12, it **begins on day 6**, not day 10. * Day 10 represents a later stage when implantation is nearly complete, but the question asks when implantation occurs (i.e., begins).

Question 1

Which one of the following best describes craniosynostosis?

Accepted Answer

It is the premature fusion of one or more cranial sutures, preventing growth perpendicular to the suture.

Answer

It is the premature fusion of one or more cranial sutures, facilitating growth perpendicular to the suture.

Answer

It is delayed fusion of one or more cranial sutures facilitating growth perpendicular to the suture.

Answer

It is delayed fusion of one or more cranial sutures preventing growth perpendicular to the suture.

Question 2

Which of the following statements with regard to Meckel's Diverticulum are correct?

1. It represents a persistent remnant of the vitellointestinal duct.
2. It is a true diverticulum of gastrointestinal tract.
3. It is most commonly found on anti-mesenteric border of ileum.
4. Heterotopic mucosa is present in 50-60% of patients.

Select the correct answer using the code given below:

Accepted Answer

1, 2 and 3

Answer

1, 3 and 4

Answer

1, 2 and 4

Answer

1 and 3

Question 3

A meningomyelocele is most commonly situated in the

Accepted Answer

Lumbosacral spine

Answer

Thoracic spine

Answer

Dorsolumbar spine

Answer

Cervical spine

Question 4

Monoamniotic monochorionic twins develop when the division of cell mass occurs

Accepted Answer

after 8th day of fertilization

Answer

after 2 weeks of development of embryonic disc

Answer

within 72 hours after fertilization

Answer

between 4th and 8th day of fertilization

Question 5

The lungs are derived from an out-pouching of the primitive foregut during which period of intrauterine life?

Accepted Answer

4th week

Answer

3rd week

Answer

5th week

Answer

6th week

Question 6

Regarding “conjoined twins”, which of the following statements is/are true?

1. These are always monozygotic
2. These result when division occurs before the embryonic disc is formed
3. Most common variety is thoracopagus

Select the correct answer using the code given below:

Accepted Answer

1 and 3 only

Answer

1 and 2 only

Answer

2 and 3 only

Answer

1, 2 and 3

Question 7

The umbilical cord normally contains:

Accepted Answer

Two arteries and one vein

Answer

One artery and two veins

Answer

One artery and one vein

Answer

Two arteries and two veins

Question 8

The external opening of branchial fistula is present in :

Accepted Answer

Lower third of the neck

Answer

Middle third of the neck

Answer

Upper third of the neck

Answer

Suprasternal notch

Question 9

Defective fusion of the Mullerian ducts may give rise to which of the following?

Accepted Answer

Uterus bicornis unicollis

Answer

Imperforate anus

Answer

Absence of the ovaries

Answer

Imperforate hymen

Question 10

Implantation of a fertilised ovum occurs on which day following fertilisation?

Accepted Answer

Day 6

Answer

Day 14

Answer

Day 20

Answer

Day 10

Embryology and Development — MCQs

Embryology and Development — MCQs

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