Embryology and Development Practice Questions

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).

Q: Which blood vessel carries deoxygenated blood back to the placenta?

Umbilical artery. ***Umbilical artery*** - The **umbilical arteries** carry **deoxygenated blood** and waste products from the fetus to the placenta [2], [3]. - There are typically **two umbilical arteries** that branch off the internal iliac arteries in the fetus [2]. *Inferior vena cava* - The **inferior vena cava** carries deoxygenated blood from the lower body back to the **fetal heart**, not the placenta. - In a fetus, the inferior vena cava also carries **oxygenated blood** from the umbilical vein through the ductus venosus [1]. *Umbilical vein* - The **umbilical vein** carries **oxygenated blood** and nutrients from the placenta to the fetus [1]. - It bypasses the liver via the **ductus venosus** to deliver blood directly to the inferior vena cava [1]. *Ductus venosus* - The **ductus venosus** is a shunt that allows **oxygenated blood** from the umbilical vein to bypass the fetal liver [1]. - It connects the umbilical vein directly to the **inferior vena cava**, not to the placenta with deoxygenated blood [1].

Q: Fingerprint first develops in how many weeks of intrauterine life?

12-16. ***12-16*** - **Fingerprint patterns**, specifically the **friction ridges** on the fingers, begin to form between 12 and 16 weeks of gestation. - This period marks the development of the **dermal papillae** and epidermal ridges that create the unique patterns. *20-24* - By 20-24 weeks, the fingerprint patterns are already **well-established** and clearly visible. - This stage is beyond the initial developmental period when the patterns first emerge. *28-32* - At 28-32 weeks, the fingerprint patterns are **fully formed** and permanent. - This timeframe is too late for the initial development of these unique dermal features. *32-36* - By 32-36 weeks, the fetus is nearing full term, and the **fingerprint morphology** is complete and stable. - The initial formation process has long since concluded before this stage.

Q: A child lacks thymus and inferior parathyroid glands. Defective development of which of the following structures is likely to be the cause?

3. ***Option 3 (Structure 3 - Third pharyngeal pouch)*** - Structure **3** represents the **third pharyngeal pouch**, which is the embryological origin of both the **thymus** and **inferior parathyroid glands**. - Defective development of the third pharyngeal pouch leads to **DiGeorge syndrome** (22q11.2 deletion syndrome), characterized by thymic hypoplasia/aplasia and hypoparathyroidism. - This explains the clinical presentation of absent thymus and inferior parathyroid glands. *Option 2 (Structure 2 - Second pharyngeal pouch)* - Structure **2** represents the **second pharyngeal pouch**. - This gives rise to the **palatine tonsils** and the **tonsillar fossa**. - Not related to thymus or parathyroid gland development. *Option 1 (Structure 1 - First pharyngeal pouch)* - Structure **1** represents the **first pharyngeal pouch**. - This develops into the **eustachian tube** (auditory tube) and **middle ear cavity** (tympanic cavity). - Not related to thymus or inferior parathyroid gland development. *Option 4 (Structure 4 - Fourth pharyngeal pouch)* - Structure **4** represents the **fourth pharyngeal pouch**. - This gives rise to the **superior parathyroid glands** (dorsal wing) and **ultimobranchial body** (ventral wing), which contributes parafollicular C cells to the thyroid gland. - Note: The inferior parathyroids (from 3rd pouch) migrate further caudally than superior parathyroids (from 4th pouch).

Q: What is the incorrect statement?

Zygote is Bipotential at 8 weeks. ***Zygote is Bipotential at 8 weeks*** - A **zygote** is formed at conception and is the single-cell diploid organism, not bipotential at 8 weeks. - The **bipotential gonad** can develop into either testes or ovaries, and this stage of sexual differentiation occurs earlier in gestation, typically around the 6th to 7th week, before differentiating into male or female gonads, not at 8 weeks as an entire zygote. *MIS inhibits the formation of Mullerian duct* - **Müllerian Inhibiting Substance (MIS)**, also known as **Anti-Müllerian Hormone (AMH)**, is produced by the Sertoli cells of the developing testes [1]. - Its primary function is to cause the **regression of the Müllerian ducts**, which would otherwise develop into female internal reproductive structures (fallopian tubes, uterus, and upper vagina) [1]. *WD form male internal genitalia* - The **Wolffian ducts (WD)**, also known as mesonephric ducts, are precursors to male internal genitalia in the presence of testosterone [1]. - stimulated by **testosterone** produced by the Leydig cells of the fetal testes, they develop into the **epididymis, vas deferens, and seminal vesicles** [1]. *DHT is necessary for the development of external genitals* - **Dihydrotestosterone (DHT)**, a more potent form of testosterone, is crucial for the development of male external genitalia [1]. - The enzyme **5α-reductase** converts testosterone to DHT in target tissues, leading to the formation of the **penis, scrotum, and prostate** [1].

Q: Identify the type of marked chromosome in the given karyotype.

Acrocentric. ***Acrocentric*** - Acrocentric chromosomes have a **centromere positioned very close to the end**, resulting in one very short arm (p arm) and one long arm (q arm). - Chromosome 13, as indicated by the arrow in the karyotype, clearly exhibits this morphology with a distinctly short p arm. *Metacentric* - **Metacentric chromosomes** have the centromere located approximately in the **middle of the chromosome**, resulting in two arms of roughly equal length. - Examples of metacentric chromosomes in a human karyotype include chromosomes 1, 3, 16, 19, and 20. *Telocentric* - **Telocentric chromosomes** have the **centromere at the very end of the chromosome**, meaning there is essentially only one arm. - This type of chromosome structure is not found in normal human karyotypes. *Submetacentric* - **Submetacentric chromosomes** have the centromere off-center, leading to one arm being **moderately shorter** than the other. - Chromosomes 2, 4-12, 17, 18, and X are generally classified as submetacentric in human karyotypes.

Q: The marked structure develops from which of the following structures?

Supracardinal vein. ***Supracardinal vein*** - The arrow points to the **azygos vein**, which drains the thoracic wall. - The azygos vein is primarily derived from the right **supracardinal vein**. *Anterior cardinal vein* - The anterior cardinal veins contribute to the formation of the **superior vena cava** and internal jugular veins. - They are located more superiorly and drain the head and upper limbs. *Subcardinal vein* - The subcardinal veins are involved in the formation of the **renal veins**, gonadal veins, and a segment of the inferior vena cava. - These veins are found in the abdominal region, inferolateral to the developing kidneys. *Common cardinal vein* - The right common cardinal vein and the proximal right anterior cardinal vein contribute to the formation of the **superior vena cava** and enter the sinus venosus. - They are important in the early embryonic stage for collecting blood from the anterior and posterior cardinal veins.

Q: During embryological development, failure of the lateral palatine processes to fuse with the primary palate results in which of the following conditions?

Isolated cleft palate. ***Isolated cleft palate*** - This condition occurs when the **lateral palatine processes** (secondary palate) **fail to fuse** with each other and/or with the **primary palate**. [1] - It results in an **opening between the oral and nasal cavities**, affecting feeding and speech. [1] *Pierre Robin sequence* - Characterized by **micrognathia**, **glossoptosis**, and often a **U-shaped cleft palate**. - While a cleft palate can be present, the defining features are the small mandible and posterior displacement of the tongue. *Submucous cleft* - Involves failure of **muscle or bone fusion under intact mucous membranes**. - It can be difficult to diagnose visually, often identified by a **bifid uvula**, notch in the hard palate, or abnormal muscle function of the soft palate. *Bifid uvula* - This is a mild form of **cleft palate**, where only the **uvula is split**. - It indicates incomplete fusion of the palatine shelves but does not represent a full failure of the lateral palatine processes to fuse with the primary palate.

Q: During development, a fetus is found to have incomplete fusion of the neural tube. Which of the following structures would most likely be affected by this developmental defect?

Spinal cord and meninges. ***Spinal cord and meninges*** - Incomplete fusion of the neural tube directly results in defects of the **neural tube closure**, which include the formation of the **spinal cord** and its protective coverings, the **meninges**. [1, 2] - Conditions like **spina bifida** (meningocele, myelomeningocele) are direct consequences of these fusion failures, exposing or abnormally developing the spinal cord and meninges. [1, 2] *Notochord* - The **notochord** is a transient embryonic structure that induces the formation of the neural tube by signaling to the overlying ectoderm; it is not directly formed by the neural tube itself. - While it plays a critical role in neural tube development, its own structural integrity is typically not primarily affected by neural tube fusion defects. *Somites* - **Somites** are blocks of paraxial mesoderm that differentiate into sclerotome (vertebrae and ribs), myotome (skeletal muscle), and dermatome (dermis of the skin). - While somite development is closely coordinated with neural tube formation, incomplete neural tube fusion primarily affects the neural structures themselves, not the somites directly. *Vertebral bodies* - **Vertebral bodies** develop from the sclerotome portion of the somites, which migrate to surround the neural tube and notochord. - While vertebral defects can be associated with severe neural tube defects (e.g., in spina bifida, the vertebral arches may fail to close), the primary defect of incomplete neural tube fusion directly impacts the neural tissue (spinal cord and meninges), with skeletal defects being secondary or associated. [1, 2]

Question 1

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 2

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

Accepted Answer

Day 6

Answer

Day 14

Answer

Day 20

Answer

Day 10

Question 3

Which blood vessel carries deoxygenated blood back to the placenta?

Accepted Answer

Umbilical artery

Answer

Inferior vena cava

Answer

Umbilical vein

Answer

Ductus venosus

Question 4

Fingerprint first develops in how many weeks of intrauterine life?

Accepted Answer

12-16

Answer

20-24

Answer

28-32

Answer

32-36

Question 5

A child lacks thymus and inferior parathyroid glands. Defective development of which of the following structures is likely to be the cause?

Accepted Answer

3

Answer

2

Answer

4

Answer

1

Question 6

What is the incorrect statement?

Accepted Answer

Zygote is Bipotential at 8 weeks

Answer

MIS inhibits the formation of Mullerian duct

Answer

WD form male internal genitalia

Answer

DHT is necessary for the development of external genitals

Question 7

Identify the type of marked chromosome in the given karyotype.

Accepted Answer

Acrocentric

Answer

Metacentric

Answer

Telocentric

Answer

Submetacentric

Question 8

The marked structure develops from which of the following structures?

Accepted Answer

Supracardinal vein

Answer

Anterior cardinal vein

Answer

Subcardinal vein

Answer

Common cardinal vein

Question 9

During embryological development, failure of the lateral palatine processes to fuse with the primary palate results in which of the following conditions?

Accepted Answer

Isolated cleft palate

Answer

Pierre Robin sequence

Answer

Submucous cleft

Answer

Bifid uvula

Question 10

During development, a fetus is found to have incomplete fusion of the neural tube. Which of the following structures would most likely be affected by this developmental defect?

Accepted Answer

Spinal cord and meninges

Answer

Notochord

Answer

Somites

Answer

Vertebral bodies

Embryology and Development — MCQs

Embryology and Development — MCQs

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