Embryology and Development Practice Questions

Q: Cells from the neural crest are involved in all except?

Wilm's tumour. ***Wilm's tumour*** - **Wilms' tumor** (nephroblastoma) is a childhood kidney cancer that arises from immature kidney cells (metanephric blastema derived from **intermediate mesoderm**), NOT neural crest cells. - This is the correct answer as it is NOT derived from neural crest cells. *Hirschsprung's disease* - Hirschsprung's disease is caused by the failure of **neural crest cells** to migrate completely during development, leading to an absence of ganglion cells (enteric nervous system) in the distal colon [1]. - This results in a functional obstruction due to lack of peristalsis in the affected segment. *Neuroblastoma* - **Neuroblastoma** is a common extracranial solid tumor in children, arising from **neural crest cells** that form the sympathetic nervous system. - It often originates in the adrenal medulla or paraspinal sympathetic ganglia. *Primitive neuroectodermal tumour* - **Note:** The classification and origin of PNETs is complex and controversial. - While traditionally included in neural crest questions, **central PNETs** (like medulloblastoma) arise from the **cerebellar neuroepithelium**, NOT neural crest [2]. - **Peripheral PNETs** (Ewing sarcoma family) may have neural crest or mesodermal origin, which remains debated. - In the context of this question, this option is considered to have neural crest involvement for traditional examination purposes.

Q: What is the duration of embryogenesis in human development?

From fertilization to the eighth week. ***From fertilization to the eighth week*** - **Embryogenesis** is the period during which the major **organ systems develop** [1]. - This critical phase begins at **fertilization** and extends through approximately the **eighth week of gestation** [1]. - The eighth week marks the end of the embryonic period, after which the **fetal period** begins [2]. *From the second week to the eighth week* - This period correctly identifies the **end of embryogenesis** but incorrectly states the **beginning**. - The first week post-fertilization involves **cleavage, morula, and blastocyst formation**, which are essential initial steps of embryonic development. - Excluding the first week misses critical early embryonic events. *From fertilization to the tenth week* - This duration is **too long** for embryogenesis, as the **ninth week marks the beginning of the fetal period** [1], [2]. - The fetal period is characterized by **growth and maturation** of already formed organ systems rather than organogenesis [2]. *From fertilization to the twelfth week* - This period is also **too long** for embryogenesis, encompassing a significant portion of the **fetal period**. - By the twelfth week, most major structures are already established and are undergoing further **development and growth**, not organogenesis.

Q: The umbilical arteries that return fetal blood to the placenta are continuous with the

Hypogastric arteries. ***Hypogastric arteries*** - The **umbilical arteries** are direct continuations of the fetal **internal iliac arteries**, which are also known as **hypogastric arteries**. [3] - These arteries carry deoxygenated blood and waste products from the fetus back to the placenta for exchange. [2], [3] *Ductus venosus* - The **ductus venosus** is a shunt that bypasses the fetal liver, allowing oxygenated blood from the umbilical vein to directly enter the **inferior vena cava**. [1] - It handles **oxygenated blood flow** from the placenta to the fetal circulation, not deoxygenated blood returning to the placenta. [1] *Portal vein* - The **portal vein** is responsible for carrying nutrient-rich blood from the gastrointestinal tract to the liver in both fetal and adult circulation. - While it receives some blood from the umbilical circulation via the umbilical vein, it is not the direct continuation of the umbilical arteries that return blood to the placenta. [1] *Inferior vena cava* - The **inferior vena cava (IVC)** carries deoxygenated blood from the lower body and oxygenated blood from the ductus venosus to the right atrium of the heart. [1], [3] - It is a large vein that brings blood to the heart, not an artery that takes blood away from the fetus to the placenta.

Q: At what stage of pregnancy do tertiary chorionic villi develop?

Day 17. **Day 17** - By **Day 17** of gestation, the **chorionic villi** have developed into their **tertiary form**, characterized by the presence of **fetal capillaries** within their mesenchymal core [1]. - This stage marks the establishment of a functional **feto-maternal exchange system** for nutrients, gases, and waste products. *Day 28* - By **Day 28**, the tertiary chorionic villi are already well-established and undergoing further **maturation** and **branching**, not just initial development. - This period is more indicative of the continued growth and specialization of the **placenta**. *Day 25* - While significant development is occurring around **Day 25**, the **tertiary villi** are generally considered to be fully formed a few days earlier. - At this point, the villi are actively engaged in early **nutrient exchange**, building on the structural foundation laid earlier. *Day 15* - At **Day 15**, the chorionic villi are typically in the **primary** or early **secondary stage** of development [1]. - **Primary villi** consist of a cytotrophoblast core covered by syncytiotrophoblast, and **secondary villi** introduce a mesenchymal core, but not yet fetal capillaries [1].

Q: A pregnant woman exposed to a teratogenic drug during the first trimester is most likely to result in which of the following defects?

Neural tube defects. ***Neural tube defects*** - The **neural tube** forms during the **third to fourth week of gestation**, representing the **earliest critical period** of organogenesis in the first trimester. Exposure to teratogens during this period can disrupt its closure. - Examples include **spina bifida** and **anencephaly**, which are severe structural malformations. - Because this is the **earliest organogenesis event**, it is the **most vulnerable** to teratogenic exposure in the first trimester, making neural tube defects the **most likely** outcome when timing is unspecified. - Classic teratogens include **valproic acid**, **carbamazepine**, and **folic acid deficiency**. *Cleft palate* - The palate develops between the **6th and 12th weeks of gestation**, which is also within the first trimester. - This is a **common teratogenic defect** associated with medications like **phenytoin**, **corticosteroids**, and **retinoids**. - However, palate formation occurs **later than neural tube closure**, making it a secondary consideration when the question asks for the "most likely" first-trimester defect. *Hypospadias* - This condition involves incomplete fusion of the **urethral folds**, which occurs during the **9th to 12th weeks of gestation** (late first to early second trimester). - While teratogens can contribute, the critical period extends beyond the first trimester, and it is **less commonly** associated with classic first-trimester teratogen exposure compared to neural tube defects. *Polydactyly* - Characterized by **extra fingers or toes**, this condition most commonly results from **genetic mutations** rather than direct teratogenic exposure. - Limb development occurs during the **fifth to ninth weeks of gestation**; while teratogens can affect limb development (e.g., thalidomide causing limb reduction), polydactyly itself is **rarely** directly linked to teratogen exposure.

Question 1

Cells from the neural crest are involved in all except?

Accepted Answer

Wilm's tumour

Answer

Hirschsprung's disease

Answer

Neuroblastoma

Answer

Primitive neuroectodermal tumour

Question 2

What is the duration of embryogenesis in human development?

Accepted Answer

From fertilization to the eighth week

Answer

From fertilization to the twelfth week

Answer

From the second week to the eighth week

Answer

From fertilization to the tenth week

Question 3

The umbilical arteries that return fetal blood to the placenta are continuous with the

Accepted Answer

Hypogastric arteries

Answer

Ductus venosus

Answer

Inferior vena cava

Answer

Portal vein

Question 4

At what stage of pregnancy do tertiary chorionic villi develop?

Accepted Answer

Day 17

Answer

Day 28

Answer

Day 25

Answer

Day 15

Question 5

A pregnant woman exposed to a teratogenic drug during the first trimester is most likely to result in which of the following defects?

Accepted Answer

Neural tube defects

Answer

Hypospadias

Answer

Cleft palate

Answer

Polydactyly

Embryology and Development — MCQs

Embryology and Development — MCQs

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