Embryology and Development Practice Questions

Q: Number of somites developed in a human fetus?

42 pairs. ### Explanation **1. Why 42 pairs is the correct answer:** Somites are bilateral blocks of paraxial mesoderm that form along the head-to-tail axis of the developing embryo. In humans, somatogenesis begins around the 20th day of gestation. Somites appear in a cranio-caudal sequence at a rate of approximately 3 pairs per day. By the end of the 5th week, a total of **42 to 44 pairs** of somites are formed. These are distributed as: * 4 Occipital * 8 Cervical * 12 Thoracic * 5 Lumbar * 5 Sacral * 8–10 Coccygeal **2. Why the other options are incorrect:** * **10 pairs (Option A):** This represents an early stage of development (approx. day 23). It is too few for a fully developed fetus. * **21 pairs (Option B):** This corresponds to the number of somites present around day 26. * **32 pairs (Option C):** This is the approximate number of somites seen at the end of the 4th week. While significant, it does not represent the final total count. **3. NEET-PG High-Yield Facts & Clinical Pearls:** * **Derivatives:** Each somite differentiates into a **Sclerotome** (vertebrae and ribs), **Myotome** (skeletal muscle), and **Dermatome** (dermis of the skin). * **Age Estimation:** The number of somites is a reliable indicator of the embryo's age during the 3rd to 5th weeks. * **Fate of Occipital Somites:** The first occipital pair and the last 5–7 coccygeal pairs eventually disappear, while the remaining occipital somites contribute to the base of the skull and muscles of the tongue (innervated by the Hypoglossal nerve). * **Clinical Correlation:** Defects in somite formation or segmentation lead to congenital vertebral anomalies like **Scoliosis** or **Klippel-Feil syndrome**.

Q: Fertilization of sperm and ova typically takes place at which site?

Ampullae. Fertilization is the process where a sperm and an oocyte unite to form a zygote [1]. In humans, this typically occurs in the **ampulla** of the fallopian tube [1]. The ampulla is the widest and longest part of the uterine tube, making it the most favorable site for the meeting of gametes [1]. The oocyte remains viable for approximately 24 hours after ovulation, during which time it resides in this region awaiting the capacitated sperm [1]. Analysis of Incorrect Options: **B. Infundibulum:** This is the funnel-shaped distal end of the tube. While it captures the ovum from the peritoneal cavity, it is not the primary site for fertilization [1]. **C. Isthmus:** This is the narrow, thick-walled medial portion of the tube. It serves as a reservoir for sperm but is generally too narrow for the initial fertilization event. **D. Fimbrial End:** These are finger-like projections at the end of the infundibulum that "sweep" the secondary oocyte into the tube [1]. They are involved in ovum pickup, not fertilization [2].

Q: A primary oocyte is formed after which process?

Mitotic division. ### Explanation The process of oogenesis begins during fetal life when primordial germ cells migrate to the ovary and undergo multiple rounds of **mitotic division** to form **oogonia**. These oogonia then undergo further mitosis and begin to differentiate into **primary oocytes**. **Why Mitotic Division is Correct:** A primary oocyte is essentially an oogonium that has completed DNA replication and entered the prophase of Meiosis I. This transition from a germ cell to a primary oocyte is driven by mitotic expansion and subsequent differentiation. By the 5th month of intrauterine life, the ovaries contain approximately 7 million oogonia, all formed via mitosis, which then transform into primary oocytes. **Why Other Options are Incorrect:** * **First Meiotic Division:** The completion of the first meiotic division (Meiosis I) occurs just before ovulation, resulting in the formation of a **secondary oocyte** and the first polar body. * **Second Meiotic Division:** The completion of the second meiotic division (Meiosis II) occurs only if fertilization takes place, resulting in a mature **ovum** (ootid) and the second polar body. **High-Yield Clinical Pearls for NEET-PG:** * **Arrest Points:** Primary oocytes are arrested in the **Dictyate stage (Prophase I)** until puberty. Secondary oocytes are arrested in **Metaphase II** until fertilization. * **Timeline:** All primary oocytes are formed before birth; no new oocytes are created postnatally. * **Number:** At birth, there are ~1–2 million primary oocytes; by puberty, only ~400,000 remain due to atresia.

Q: Which of the following statements regarding the umbilical cord is TRUE?

Contains two arteries and one vein. ### Explanation The umbilical cord is the vital conduit between the developing fetus and the placenta. Understanding its anatomy is high-yield for NEET-PG [2]. **1. Why Option A is Correct:** The mature umbilical cord typically contains **two umbilical arteries** and **one umbilical vein**, all embedded in a gelatinous substance called **Wharton’s jelly** [2]. * **Umbilical Arteries:** Carry deoxygenated blood and waste products from the fetus to the placenta [4]. * **Umbilical Vein:** Carries oxygenated and nutrient-rich blood from the placenta to the fetus [3], [4]. **2. Why the Other Options are Incorrect:** * **Option B:** The umbilical cord pulsation rate **corresponds to the fetal heart rate**, not the maternal rate. This is because the blood flowing through the cord is pumped by the fetal heart. * **Option C:** The umbilical cord is covered only by the **amnion**. The chorion contributes to the placenta but does not wrap around the cord [1]. * **Option D:** While there are initially two umbilical veins during early embryonic development, the **right umbilical vein normally regresses** by the 6th week, leaving only the left umbilical vein. **3. Clinical Pearls for NEET-PG:** * **Single Umbilical Artery (SUA):** Seen in about 1% of pregnancies; it is a marker for increased risk of congenital anomalies (especially renal and cardiac) and chromosomal trisomies (Trisomy 18). * **Wharton’s Jelly:** Derived from extraembryonic mesoderm; it prevents the compression of the vessels. * **Remnants:** The umbilical cord may contain remnants of the **allantois** and the **vitelline duct** (yolk stalk) [2]. * **False Knots:** These are simply focal accumulations of Wharton's jelly or redundant vessel loops, unlike true knots which can cause fetal distress [2].

Q: During which fetal developmental stage do the testes descend into the scrotum?

End of 8th month. The descent of the testes is a complex physiological process occurring in two distinct phases: the **trans-abdominal phase** and the **inguino-scrotal phase**. 1. **Why the Correct Answer is Right:** The testes reach the deep inguinal ring by the 3rd month of gestation. They remain there until the 7th month, after which they pass through the inguinal canal. The final stage of descent into the scrotum occurs during the **end of the 8th month** (approximately 32 weeks). This process is mediated by the shortening of the **gubernaculum** and influenced by androgens and Calcitonin Gene-Related Peptide (CGRP). 2. **Analysis of Incorrect Options:** * **6th Month:** At this stage, the testes are still located near the deep inguinal ring, having not yet entered the inguinal canal. * **7th Month:** This marks the *beginning* of the migration through the inguinal canal, not the completion into the scrotum. * **9th Month:** By the 9th month (full term), the testes should already be present in the scrotum. If they are not descended by birth, the condition is termed cryptorchidism. **High-Yield Clinical Pearls for NEET-PG:** * **Cryptorchidism:** The most common site for an undescended testis is the **inguinal canal**. * **Processus Vaginalis:** Failure of this peritoneal fold to obliterate after descent can lead to **congenital indirect inguinal hernia** or **hydrocele**. * **Ectopic Testis:** Occurs when the testis deviates from the normal path of descent, most commonly found in the **superficial inguinal pouch**. * **Thermoregulation:** The primary physiological reason for descent is that spermatogenesis requires a temperature 2–3°C lower than the core body temperature.

Q: The central tendon of the diaphragm is derived from which embryonic structure?

Septum transversum. The diaphragm is a composite structure formed by the fusion of four embryonic components. Understanding its development is a high-yield topic for NEET-PG. ### **1. Why Septum Transversum is Correct** The **septum transversum** is a thick plate of mesodermal tissue that initially lies between the primitive heart and the liver [1]. During development, it migrates caudally, carrying the phrenic nerve with it. It forms the **central tendon** of the diaphragm, which serves as the non-contractile structural foundation of the muscle [1]. ### **2. Explanation of Incorrect Options** * **B. Pleuroperitoneal membrane:** These membranes close the pericardioperitoneal canals. They contribute to the **small peripheral portions** of the diaphragm. Failure of these to fuse results in Congenital Diaphragmatic Hernia (Bochdalek). * **C. Dorsal mesogastrium:** This forms the **crura** of the diaphragm (the muscular pillars surrounding the esophagus). * **D. Ventral mesogastrium:** This does not contribute to the diaphragm; it gives rise to the lesser omentum and the falciform ligament [1]. ### **3. High-Yield Clinical Pearls for NEET-PG** * **Mnemonic for Diaphragm Development:** "**S**everal **P**arts **B**uild **D**iaphragm" (**S**eptum transversum, **P**leuroperitoneal membranes, **B**ody wall (muscular ingrowth), **D**orsal mesentery of esophagus). * **Nerve Supply:** The diaphragm is supplied by the **Phrenic Nerve (C3, C4, C5)**. The "C3, 4, 5 keep the diaphragm alive" rule exists because the septum transversum originates at the cervical level before descending. * **Bochdalek Hernia:** The most common congenital diaphragmatic hernia; occurs posterolaterally (usually on the **left**) due to failure of the pleuroperitoneal membrane to close. * **Morgagni Hernia:** Occurs anteriorly through the space between the xiphoid and costal origins.

Q: The embryo implants on the endometrium after how many days of fertilization?

7-9 days. The process of implantation is a critical milestone in embryology. Following fertilization in the ampulla of the fallopian tube, the zygote undergoes cleavage while traveling toward the uterus [1]. It reaches the uterine cavity as a **morula** (16-cell stage) on day 3-4 [1]. It then transforms into a **blastocyst**. Implantation begins when the blastocyst attaches to the endometrial epithelium, typically starting on **day 6** and completing by **day 10-12** [3]. The peak window for initial attachment and firm embedding occurs between **7-9 days** post-fertilization [3]. **Analysis of Options:** * **A (3-5 days):** During this period, the embryo is still a morula or an early blastocyst either in the fallopian tube or just entering the uterine cavity; it has not yet initiated implantation [1]. * **B (7-9 days):** **Correct.** This represents the "Implantation Window" where the trophoblast differentiates into syncytiotrophoblast and cytotrophoblast to invade the secretory phase endometrium [2]. * **C (10 days):** By day 10, the blastocyst is almost completely embedded in the endometrial stroma [2]. While implantation is ongoing, the process starts significantly earlier. * **D (16 days):** This is well into the second week of development (period of gastrulation/primitive streak formation). By this time, the uteroplacental circulation is already establishing. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Implantation:** Most commonly the upper part of the posterior wall of the uterine body. * **Decidual Reaction:** The morphological changes in endometrial cells (becoming polyhedral and loaded with glycogen) to support the embryo [4]. * **hCG Secretion:** Secreted by the **syncytiotrophoblast**; it can be detected in maternal blood by day 8-9, serving as the basis for pregnancy tests [3]. * **Zona Pellucida:** Must be shed ("hatching") before implantation can occur [1].

Question 1

Number of somites developed in a human fetus?

Accepted Answer

42 pairs

Answer

10 pairs

Answer

21 pairs

Answer

32 pairs

Question 2

During week 2 of development, how does the embryoblast receive its nutrients?

Accepted Answer

Diffusion

Answer

Osmosis

Answer

Reverse osmosis

Answer

Fetal capillaries

Question 3

Which is the first germ layer to be formed during embryonic development?

Accepted Answer

Endoderm

Answer

Ectoderm

Answer

Mesoderm

Answer

All of them develop simultaneously

Question 4

Fertilization of sperm and ova typically takes place at which site?

Accepted Answer

Ampullae

Answer

Infundibulum

Answer

Isthmus

Answer

Fimbrial End

Question 5

A patient, who appears to be female, is found to be 46XY in genotype. The patient's vagina is very shallow, ending in a blind pouch, and there are palpable masses in the labia. The diagnosis of testicular feminization syndrome is made. Which of the following was most likely present during the early fetal life of this individual?

Accepted Answer

Mullerian inhibitory factor

Answer

A streak ovary

Answer

A uterus

Answer

An oviduct

Question 6

A primary oocyte is formed after which process?

Accepted Answer

Mitotic division

Answer

First meiotic division

Answer

Second meiotic division

Answer

None of the above

Question 7

Which of the following statements regarding the umbilical cord is TRUE?

Accepted Answer

Contains two arteries and one vein

Answer

The umbilical cord pulsation rate does not correspond to the maternal pulsation rate

Answer

It is covered by the amnion and chorion

Answer

It contains two veins

Question 8

During which fetal developmental stage do the testes descend into the scrotum?

Accepted Answer

End of 8th month

Answer

6th month

Answer

7th month

Answer

9th month

Question 9

The central tendon of the diaphragm is derived from which embryonic structure?

Accepted Answer

Septum transversum

Answer

Pleuroperitoneal membrane

Answer

Dorsal mesogastrium

Answer

Ventral mesogastrium

Question 10

The embryo implants on the endometrium after how many days of fertilization?

Accepted Answer

7-9 days

Answer

3-5 days

Answer

10 days

Answer

16 days

Embryology and Development — MCQs

Embryology and Development — MCQs

On this page

Practice by Chapter

Want unlimited practice?