Embryology and Development Practice Questions

Q: All of the following structures arise from the mesonephric duct except?

Appendix of testis. The development of the male reproductive system is a high-yield topic for NEET-PG. To answer this question, one must distinguish between structures derived from the **Mesonephric (Wolffian) duct** and those derived from the **Paramesonephric (Müllerian) duct**. [1] ### 1. Why "Appendix of testis" is the correct answer: The **Appendix of testis** is a vestigial remnant of the cranial end of the **Paramesonephric (Müllerian) duct**. In males, the Müllerian ducts largely regress due to Müllerian Inhibiting Substance (MIS) secreted by Sertoli cells. Only two remnants persist: the Appendix of testis (cranial end) and the Prostatic utricle (caudal end). [1] ### 2. Why the other options are incorrect: Under the influence of testosterone (from Leydig cells), the **Mesonephric (Wolffian) duct** differentiates into the following male genital excretory passages: [1] * **Epididymis:** Formed from the highly coiled proximal part of the duct. * **Ductus (Vas) deferens:** Formed from the thick-walled intermediate part. [1] * **Ejaculatory duct:** Formed from the terminal part of the duct, distal to the seminal vesicle bud. * **Seminal vesicles:** Arise as lateral outgrowths from the distal mesonephric duct. ### 3. Clinical Pearls & High-Yield Facts: * **Mnemonic (SEED):** **S**eminal vesicles, **E**pididymis, **E**jaculatory duct, and **D**uctus deferens all come from the Wolffian duct. * **Appendix of Epididymis:** Unlike the appendix of the testis, the appendix of the epididymis is a remnant of the **Mesonephric duct**. * **Torsion:** The appendix of the testis can undergo torsion (common in children), presenting as a "blue dot sign" on the scrotum, mimicking testicular torsion. * **Trigon of Bladder:** The mesonephric ducts also contribute to the development of the vesical trigone.

Q: All are ectodermal in origin except?

Bone marrow. ### Explanation The correct answer is **D. Bone marrow**. **1. Why Bone Marrow is the Correct Answer:** The bone marrow, along with the skeletal system, muscles, circulatory system (heart and blood vessels), and connective tissues, is derived from the **Mesoderm**. Specifically, the hematopoietic stem cells within the bone marrow originate from the mesodermal layer during embryogenesis [1]. **2. Analysis of Incorrect Options (Ectodermal Derivatives):** * **A. External acoustic meatus:** This is derived from the **surface ectoderm** (specifically the dorsal end of the first pharyngeal cleft). * **B. Anal canal:** The anal canal has a dual origin. The part **below the pectinate line** is derived from the **proctodeum (surface ectoderm)**, while the part above is endodermal. Since the question asks for "ectodermal in origin," this fits the criteria. * **C. Sebaceous gland:** All skin appendages, including sweat glands, sebaceous glands, hair follicles, and nails, are derivatives of the **surface ectoderm** [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Rule of Thumb:** "Ectoderm" forms the "Attract-oderm" (things that make you attractive: skin, hair, brain/intelligence). * **Neuroectoderm vs. Surface Ectoderm:** * *Neuroectoderm:* CNS (Brain, Spinal cord), Retina, Posterior Pituitary. * *Surface Ectoderm:* Lens of the eye, Inner ear, Anterior Pituitary (Rathke’s pouch), and Parotid gland. * **Microglia Exception:** While most of the nervous system is ectodermal, **Microglia** are mesodermal in origin (the "M" in Microglia stands for Mesoderm). * **Adrenal Gland:** The Cortex is Mesodermal, while the Medulla is Neural Crest (Ectodermal).

Q: Double arch of aorta is seen in which of the following conditions?

All of the above. The correct answer is **D. All of the above** because all three options represent different clinical manifestations of the same underlying genetic etiology: **22q11.2 deletion syndrome.** **1. The Underlying Concept:** The 22q11.2 deletion syndrome is a result of the defective development of the **3rd and 4th pharyngeal pouches**. This leads to a spectrum of anomalies involving the heart, parathyroid glands, and thymus. **Double Aortic Arch** is a classic vascular ring anomaly associated with this deletion, occurring when the right dorsal aorta persists along with the left dorsal aorta, encircling the trachea and esophagus [1]. **2. Breakdown of Options:** * **CATCH22:** This is a popular mnemonic used to describe the clinical features of 22q11.2 deletion: **C**ardiac defects (like Double Aortic Arch, Tetralogy of Fallot), **A**bnormal facies, **T**hymic hypoplasia, **C**left palate, and **H**ypocalcemia. * **DiGeorge Syndrome:** This is the most well-known phenotype of the 22q11.2 deletion, characterized primarily by immune deficiency (thymic aplasia) and hypocalcemia. * **Velo-cardio-facial Syndrome (Shprintzen Syndrome):** This is another variant of the same genetic deletion, focusing more on cleft palate (Velo-), cardiac defects (-cardio-), and distinct facial features (-facial). Since all three terms refer to the same genetic microdeletion syndrome, they all share the risk of aortic arch anomalies. **High-Yield Clinical Pearls for NEET-PG:** * **Embryology:** Double aortic arch results from the failure of the **right dorsal aorta** to regress. * **Clinical Presentation:** It forms a "vascular ring" that can compress the trachea (causing stridor) and esophagus (causing dysphagia lusoria) [1]. * **Diagnosis:** Barium swallow shows bilateral indentations on the esophagus; Gold standard is CT/MRI angiography [1]. * **Genetic Marker:** 22q11.2 deletion is the most common microdeletion in humans.

Q: In the production of female gametes, which of the following cells can remain dormant for 12-40 years?

Primary oocyte. The correct answer is **Primary oocyte**. This question tests the understanding of the unique timeline of female gametogenesis (oogenesis). **Why Primary Oocyte is Correct:** During fetal development (around the 5th month), oogonia enter the first meiotic division to become **primary oocytes**. However, they do not complete meiosis I. Instead, they are arrested in the **diplotene stage of prophase I** (facilitated by Oocyte Maturation Inhibitor - OMI). These cells remain dormant in this arrested state from birth until puberty [1]. Starting at puberty, small cohorts are recruited during each ovarian cycle. Since ovulation can occur anytime between menarche (age ~12) and menopause (age ~50), these primary oocytes can remain dormant for **12 to 50 years** [1]. **Why Other Options are Incorrect:** * **A. Primordial germ cells:** These are the earliest undifferentiated stem cells that migrate from the yolk sac to the genital ridge by the 5th-6th week of gestation. They quickly differentiate into oogonia and do not remain dormant for years. * **C. Secondary oocyte:** This is formed only just before ovulation when the primary oocyte completes meiosis I [2]. It is arrested in **metaphase II** and survives for only 12–24 hours unless fertilized. * **D. First polar body:** This is a byproduct of the completion of meiosis I [2]. It is a non-functional cell that typically degenerates shortly after formation. **High-Yield NEET-PG Pearls:** * **Arrest Points:** Primary oocyte = **P**rophase I (**D**iplotene); Secondary oocyte = **M**etaphase II (Mnemonic: **P**rimary-**P**rophase; **S**econdary-**S**econd metaphase). * **Dictyotene:** The specific resting stage within the diplotene stage is often called the *dictyate* or *dictyotene* stage [1]. * **Completion of Meiosis II:** This only occurs if **fertilization** takes place. If no sperm enters, the secondary oocyte never completes meiosis.

Q: The second arch artery persists for some part of fetal life as which of the following?

Stapedial artery. The aortic arches are a series of six pairs of mesenchymal vessels that arise from the aortic sac. Each arch is associated with a specific pharyngeal arch and undergoes a unique pattern of regression or transformation. ### **Explanation of the Correct Answer** **Option B (Stapedial artery)** is correct. The **second aortic arch** (Hyoid arch) largely disappears, but its dorsal portion persists during fetal life as the **stapedial artery**. This vessel passes through the ring of the stapes. While it typically atrophies in humans before birth (leaving behind the foramen in the stapes), its remnants contribute to the development of the caroticotympanic arteries. ### **Analysis of Incorrect Options** * **Option A (Maxillary artery):** This is derived from the **first aortic arch**. While most of the first arch disappears, a small portion persists as the maxillary artery and contributes to the external carotid artery. * **Option C (Subclavian artery):** The **right** subclavian artery is formed by the **fourth right aortic arch**, the right dorsal aorta, and the right seventh intersegmental artery. The **left** subclavian artery is derived primarily from the **left seventh intersegmental artery**. ### **NEET-PG High-Yield Pearls** * **1st Arch:** Maxillary artery (Mnemonic: **1**st is **M**axillary). * **2nd Arch:** Stapedial and Hyoid arteries (Mnemonic: **S**econd is **S**tapedial). * **3rd Arch:** Common Carotid and proximal part of Internal Carotid artery (Mnemonic: **C** is the **3**rd letter). * **4th Arch:** Left side forms the **Arch of Aorta**; Right side forms the **Right Subclavian artery**. * **6th Arch:** Left side forms the **Ductus Arteriosus** and Left Pulmonary artery; Right side forms the Right Pulmonary artery. * **Clinical Note:** A persistent stapedial artery is a rare vascular anomaly that can cause pulsatile tinnitus or complicate middle ear surgery.

Q: Anal opening is formed in which week of embryonic development?

7th. The development of the anal opening is a critical event in the partitioning of the hindgut. During the **7th week** of embryonic development, the **urorectal septum** (a wedge of mesoderm) grows caudally to fuse with the **cloacal membrane**. This fusion divides the cloaca into two distinct parts: the primitive urogenital sinus (anteriorly) and the anorectal canal (posteriorly). Simultaneously, the cloacal membrane is divided into the urogenital membrane and the **anal membrane**. By the end of the 7th week, the anal membrane ruptures, creating a patent communication between the rectum and the exterior, thus forming the **anal opening** [1]. **Analysis of Options:** * **Option A (5th week):** During this stage, the urorectal septum is just beginning to divide the cloaca; the membranes are still intact and the openings are not yet formed. * **Option B (7th week):** **Correct.** This is the definitive period when the anal membrane ruptures to establish the anal orifice [1]. * **Option C (10th week):** By this time, the gastrointestinal tract is undergoing rotation and physiological herniation return; the anal opening is already well-established. **High-Yield Clinical Pearls for NEET-PG:** * **Dual Origin of Anal Canal:** The upper 2/3rd (above the pectinate line) is derived from **endoderm** (hindgut), while the lower 1/3rd (below the pectinate line) is derived from **ectoderm** (proctodeum). * **Imperforate Anus:** This clinical condition occurs if the anal membrane fails to perforate during the 7th-8th week. * **Pectinate Line:** This represents the site of the former anal membrane and serves as a landmark for differences in blood supply, nerve supply, and lymphatic drainage.

Q: By which day after fertilization is placental circulation established?

17th day. ### Explanation The establishment of placental circulation is a multi-step process involving the development of the chorionic villi and the fetal cardiovascular system. **Why 17th Day is Correct:** By the **17th day** after fertilization, the fetal blood vessels (derived from the extraembryonic mesoderm) within the **tertiary villi** become functional [1]. These vessels connect with the developing embryonic heart tube. At this stage, the fetal blood begins to circulate through the capillaries of the villi, and the **placental (fetoplacental) circulation** is officially established [1]. This allows for the exchange of nutrients and gases between the maternal blood (in the intervillous spaces) and fetal blood. **Analysis of Incorrect Options:** * **11th Day:** This marks the formation of **lacunae** within the syncytiotrophoblast [1]. While maternal blood begins to flow into these lacunae (primordial uteroplacental circulation), the fetal component is not yet developed. * **13th Day:** This is characterized by the appearance of **primary villi** (proliferations of cytotrophoblast covered by syncytiotrophoblast) [1]. No blood vessels are present in the villi yet. * **15th Day:** This corresponds to the formation of **secondary villi**, where extraembryonic mesoderm invades the core of the primary villi. However, these mesenchymal cells have not yet differentiated into blood vessels. **NEET-PG High-Yield Pearls:** * **Primary Villi:** Trophoblast only (Day 13) [1]. * **Secondary Villi:** Trophoblast + Mesoderm core (Day 15). * **Tertiary Villi:** Trophoblast + Mesoderm + **Capillaries** (Day 17-21). * **Heart Beat:** The embryonic heart starts beating around **Day 21-22**, which is when the circulation becomes fully effective. * **Uteroplacental vs. Fetoplacental:** Maternal blood enters lacunae by Day 11-12 (Uteroplacental), but the fetal circuit (Fetoplacental) requires tertiary villi (Day 17) [1].

Q: Muscles of facial expression develop from which embryonic arch?

Second Arch. The muscles of facial expression develop from the **mesoderm of the Second Pharyngeal Arch** (also known as the Hyoid Arch). In embryology, each pharyngeal arch is associated with a specific cranial nerve that supplies all the structures derived from that arch. The nerve of the second arch is the **Facial Nerve (CN VII)**; therefore, all muscles supplied by the facial nerve—including the muscles of facial expression, stapedius, stylohyoid, and the posterior belly of the digastric—originate from this arch. **Analysis of Options:** * **First Arch (Mandibular Arch):** Associated with the **Trigeminal Nerve (V3)**. It gives rise to the muscles of mastication (tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of digastric). * **Third Arch:** Associated with the **Glossopharyngeal Nerve (CN IX)**. It gives rise to a single muscle: the **Stylopharyngeus**. * **Fourth Arch:** Associated with the **Superior Laryngeal branch of the Vagus Nerve (CN X)**. It gives rise to the cricothyroid muscle and the levator veli palatini. **High-Yield Clinical Pearls for NEET-PG:** * **Skeletal Derivatives:** The second arch also forms the stapes, styloid process, stylohyoid ligament, and the lesser cornu (and upper body) of the hyoid bone. * **Golden Rule:** If you know the nerve supply of a muscle, you can deduce its arch of origin. * CN V = 1st Arch * CN VII = 2nd Arch * CN IX = 3rd Arch * CN X = 4th & 6th Arches * **Treacher Collins Syndrome:** Results from the failure of first arch neural crest cells to migrate, leading to mandibular hypoplasia and facial abnormalities.

Q: The vitelline vein develops into which of the following vascular structures?

Hepatic vein. **Explanation:** The vitelline veins (omphalomesenteric veins) are responsible for carrying blood from the yolk sac to the sinus venosus. As the liver develops within the septum transversum, the vitelline veins form a complex anastomotic network around the duodenum [1], which eventually gives rise to: 1. **Hepatic Sinusoids:** Formed by the fragmentation of the veins by the growing liver cords [1]. 2. **Hepatic Veins:** Derived from the proximal portion of the right vitelline vein [4]. 3. **Portal Vein:** Formed from the anastomotic network around the duodenum [3]. 4. **Superior Mesenteric Vein:** Derived from the distal part of the right vitelline vein [3]. **Analysis of Incorrect Options:** * **B. Azygos vein:** This is derived from the **Right Supracardinal vein** (part of the cardinal venous system), which drains the body wall. * **C. Inferior mesenteric vein:** This develops from the **subcardinal/cardinal system** and vitelline tributaries, but it is not a direct derivative of the vitelline trunk itself in the same way the hepatic/portal systems are. * **D. Splenic vein:** This develops from the dorsal mesentery veins and joins the portal system; it is not a primary derivative of the vitelline veins [3]. **NEET-PG High-Yield Pearls:** * **Left Vitelline Vein:** Mostly regresses; the persistent part contributes to the hepatic sinusoids. * **Right Vitelline Vein:** Forms the **Inferior Vena Cava (Hepatic segment)**, the Portal vein, and the Superior Mesenteric vein [2]. * **Umbilical Veins:** The **Right** umbilical vein disappears completely; the **Left** umbilical vein persists to carry oxygenated blood from the placenta to the liver [2] (becoming the *Ligamentum teres* after birth).

Question 1

All of the following structures arise from the mesonephric duct except?

Accepted Answer

Appendix of testis

Answer

Epididymis

Answer

Ductus deferens

Answer

Ejaculatory duct

Question 2

Which of the following is an exception to the non-development of Wolffian duct structures?

Accepted Answer

Incomplete Androgen Insensitivity Syndrome (AIS)

Answer

Swyer syndrome

Answer

Testicular feminization syndrome

Answer

Turner syndrome

Question 3

All are ectodermal in origin except?

Accepted Answer

Bone marrow

Answer

External acoustic meatus

Answer

Anal canal

Answer

Sebaceous gland

Question 4

Double arch of aorta is seen in which of the following conditions?

Accepted Answer

All of the above

Answer

CATCH22

Answer

Di George syndrome

Answer

Velo cardiofacial syndrome

Question 5

In the production of female gametes, which of the following cells can remain dormant for 12-40 years?

Accepted Answer

Primary oocyte

Answer

Primordial germ cell

Answer

Secondary oocyte

Answer

First polar body

Question 6

The second arch artery persists for some part of fetal life as which of the following?

Accepted Answer

Stapedial artery

Answer

Maxillary artery

Answer

Subclavian artery

Answer

None of the above

Question 7

Anal opening is formed in which week of embryonic development?

Accepted Answer

7th

Answer

5th

Answer

10th

Answer

None of the above

Question 8

By which day after fertilization is placental circulation established?

Accepted Answer

17th day

Answer

11th day

Answer

13th day

Answer

15th day

Question 9

Muscles of facial expression develop from which embryonic arch?

Accepted Answer

Second Arch

Answer

First Arch

Answer

Third Arch

Answer

Fourth Arch

Question 10

The vitelline vein develops into which of the following vascular structures?

Accepted Answer

Hepatic vein

Answer

Azygos vein

Answer

Inferior mesenteric vein

Answer

Splenic vein

Embryology and Development — MCQs

Embryology and Development — MCQs

On this page

Practice by Chapter

Want unlimited practice?