Embryology and Development — MCQs
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What is the anatomical location of the testis during the 24-28 weeks of intrauterine life?
What is the skeletal derivative of the first arch?
Which arch artery contributes to the formation of the aortic arch that influences the course of the left recurrent laryngeal nerve?
Which of the following statements about skin is false?
The structure marked A in the image below gives rise to which of the following structures?
Which of the following is a remnant of the Wolffian duct in females?
The most common site of the branchial cyst is:
Nerves of the Branchial arches are derived from:
Which of the following muscles is derived from the first pharyngeal arch?
Ureteric bud develops from:
Embryology and Development Indian Medical PG Practice Questions and MCQs
Question 1091: What is the anatomical location of the testis during the 24-28 weeks of intrauterine life?
- A. Superficial inguinal ring
- B. Inguinal region
- C. Scrotal region
- D. Deep inguinal ring (Correct Answer)
Explanation: Deep inguinal ring - Between **24-28 weeks of gestation**, the testes are typically located in the **deep inguinal ring**, preparing for their descent into the scrotum. - This stage represents a crucial period in testicular descent, positioning the testes at the entrance to the inguinal canal. *Inguinal region* - While the testes pass through the inguinal region during descent, this term is too broad to pinpoint their exact location at **24-28 weeks**. - The inguinal region encompasses both the **deep and superficial inguinal rings**, as well as the inguinal canal itself. *Scrotal region* - The testes typically reach the **scrotal region** much later, usually by **30-32 weeks of gestation** or shortly before birth. - Their presence in the scrotum at **24-28 weeks** would be considered premature descent. *Superficial inguinal ring* - The testes pass through the **superficial inguinal ring** after traversing the inguinal canal, usually after **28 weeks**, on their way to the scrotum. - Before **28 weeks**, they are generally located more proximally, around the deep inguinal ring.
Question 1092: What is the skeletal derivative of the first arch?
- A. Stapes
- B. Maxilla (Correct Answer)
- C. Laryngeal cartilages
- D. Hyoid bone
Explanation: Maxilla - The **first pharyngeal arch** forms the maxilla, which is derived from its **dorsal portion**. - This arch also gives rise to the **mandible**, zygoma, and squamous temporal bone. *Stapes* - The **stapes** is a derivative of the **second pharyngeal arch**. - This arch also forms the **styloid process**, lesser horn of the hyoid, and parts of the temporal bone. *Laryngeal cartilages* - The laryngeal cartilages (thyroid, cricoid, arytenoid) are derived from the **fourth and sixth pharyngeal arches**. - These arches give rise to structures involved in the **larynx** and pharynx. *Hyoid bone* - The **hyoid bone** has a dual origin: the **lesser horn and upper body** are from the **second pharyngeal arch**, while the **greater horn and lower body** are from the **third pharyngeal arch**. - It does not exclusively originate from the first arch.
Question 1093: Which arch artery contributes to the formation of the aortic arch that influences the course of the left recurrent laryngeal nerve?
- A. 4th arch (Correct Answer)
- B. 3rd arch
- C. 5th arch
- D. 2nd arch
Explanation: ***4th arch*** - The **left fourth aortic arch artery** gives rise to the **aortic arch** distal to the origin of the left subclavian artery. - The left recurrent laryngeal nerve hooks around the **ductus arteriosus** (a remnant of the 6th arch artery) and the aortic arch, making its course dependent on the development of the 4th aortic arch [1]. *3rd arch* - The **third aortic arch arteries** primarily contribute to the formation of the common carotid arteries and the proximal part of the internal carotid arteries. - These arteries are located superior to the structures that influence the recurrent laryngeal nerve's path. *5th arch* - The **fifth aortic arch arteries** are **rudimentary** or absent in humans. - They do not significantly contribute to the formation of major arterial structures in the adult, nor do they influence the recurrent laryngeal nerve. *2nd arch* - The **second aortic arch arteries** give rise to the stapedial arteries, which usually regress. - They are not involved in the formation of the great vessels in the mediastinum or the course of the recurrent laryngeal nerve.
Question 1094: Which of the following statements about skin is false?
- A. Most of the cells in skin are keratinocytes derived from ectoderm
- B. Dermis is made up of type 1 and type 3 collagen in 4:1 ratio
- C. Both dermis & epidermis are derived from ectoderm (Correct Answer)
- D. Skin accounts for total of 15% of body weight
Explanation: Both dermis & epidermis are derived from ectoderm - This statement is **FALSE** because the **epidermis is derived from the ectoderm**, but the **dermis is derived from the mesoderm**. - The ectoderm forms the outer layer of the embryo, giving rise to the epidermis, while the mesoderm forms the connective tissues, including the dermis. - This is the correct answer to this "false" question. [1] *Most of the cells in skin are keratinocytes derived from ectoderm* - This is **TRUE**. **Keratinocytes** constitute approximately **90% of the epidermal population**. - They are indeed derived from the **embryonic ectoderm**, which is the primary germ layer for the epidermis. [1] *Dermis is made up of type 1 and type 3 collagen in 4:1 ratio* - This is **TRUE**. The dermis is primarily composed of **collagen fibers**, with **Type I collagen** being the most abundant (80-90%). - **Type III collagen** is also present, and the ratio of **Type I to Type III collagen is approximately 4:1 to 5:1** in normal mature dermis. *Skin accounts for total of 15% of body weight* - This is **TRUE**. The skin is the **largest organ** of the body, and its weight typically constitutes around **15-20% of an adult's total body weight**. - This significant proportion reflects its extensive surface area and multiple essential functions. [1]
Question 1095: The structure marked A in the image below gives rise to which of the following structures?
- A. Lienorenal ligament
- B. Gastrophrenic ligament
- C. Gastrosplenic ligament
- D. Falciform ligament (Correct Answer)
Explanation: ***Falciform ligament*** - The structure marked 'A' represents the **ventral mesentery** in the embryonic stage, which connects the primitive gut tube to the anterior body wall. - The **falciform ligament** develops from the ventral mesentery, specifically in the region of the liver, and connects the liver to the anterior abdominal wall and diaphragm. *Gastrosplenic ligament* - This ligament is derived from the **dorsal mesentery**, not the ventral mesentery. - It connects the greater curvature of the stomach to the hilum of the spleen. *Lienorenal ligament* - Also derived from the **dorsal mesentery**, connecting the left kidney to the spleen. - This structure is not formed from the ventral mesentery which is indicated by 'A'. *Gastrophrenic ligament* - This ligament is part of the **dorsal mesentery** and connects the stomach to the diaphragm. - It is not a derivative of the ventral mesentery.
Question 1096: Which of the following is a remnant of the Wolffian duct in females?
- A. Pouch of Douglas
- B. Uterovesical pouch
- C. Gartner’s cyst (Correct Answer)
- D. Broad ligament
Explanation: ***Gartner’s cyst*** - **Gartner's cysts** are remnants of the **Wolffian duct (mesonephric duct)** in females [3]. These ducts normally regress in females but can persist as vestigial structures [3]. - They typically present as cysts or small ducts along the lateral walls of the vagina or in the broad ligament [2], [3]. *Pouch of Douglas* - The **Pouch of Douglas (rectouterine pouch)** is a peritoneal recess located between the rectum and the uterus, not a remnant of the Wolffian duct [2]. - It is formed during development as the peritoneum drapes over the pelvic organs. *Uterovesical pouch* - The **uterovesical pouch** is a peritoneal reflection located between the uterus and the bladder, separate from the Wolffian duct remnants [1]. - Like the Pouch of Douglas, it is a normal anatomical space formed by the arrangement of the peritoneum in the pelvis. *Broad ligament* - The **broad ligament** is a wide fold of peritoneum that supports the uterus, fallopian tubes, and ovaries. It is not a remnant of the Wolffian duct itself, though Wolffian duct remnants (like Gartner's ducts) can sometimes be found within it [3]. - It serves as a mesentery for the reproductive organs, connecting them to the lateral walls of the pelvis.
Question 1097: The most common site of the branchial cyst is:
- A. Posterior border of sternocleidomastoid
- B. Anterior border of sternocleidomastoid (Correct Answer)
- C. Digastric muscle
- D. Omohyoid muscle
Explanation: ***Anterior border of sternocleidomastoid*** - Branchial cysts most commonly present as a mass along the **anterior border of the sternocleidomastoid muscle**, typically in the upper to middle third of the neck [3]. - This location corresponds to the embryological remnants of the **second branchial cleft**. *Posterior border of sternocleidomastoid* - Cysts or masses in this region are less likely to be branchial cysts and might indicate other conditions like **lymphadenopathy** or a **cystic hygroma** [1]. - The posterior border is not the typical embryological location for branchial cleft remnants to form cysts. *Digastric muscle* - While the digastric muscle is located in the neck, cysts directly associated with this muscle are rare and usually of **different embryological origin** (e.g., salivary gland cysts or submandibular space infections). - Branchial cysts are specifically tied to the branchial apparatus remnants. *Omohyoid muscle* - The omohyoid muscle crosses the lower neck, and masses in its vicinity are typically not branchial cysts but could involve **thyroid pathology**, **lymph nodes**, or **vascular anomalies** [2]. - This location is anatomically distinct from the typical presentation of a branchial cleft cyst.
Question 1098: Nerves of the Branchial arches are derived from:
- A. Mesoderm
- B. Neuroectoderm (Correct Answer)
- C. Endoderm
- D. Neural crest
Explanation: ***Neuroectoderm*** - The **cranial nerves** (CN V, VII, IX, X) that supply the branchial arches are derived from **neuroectoderm**. - **Motor components** arise from motor nuclei in the brainstem (neural tube derivative). - **Sensory components** arise from sensory nuclei in the brainstem and from ectodermal placodes. - Neuroectoderm gives rise to the **neurons** that form the actual nerve fibers innervating branchial arch derivatives. *Neural crest* - While neural crest cells migrate extensively and are crucial to branchial arch development, they do **not** form the nerves themselves. - Neural crest contributes to **sensory and autonomic ganglia**, **Schwann cells**, and other supporting structures. - The actual **nerve fibers (axons)** of cranial nerves come from neuroectodermal neurons, not neural crest. *Mesoderm* - **Mesoderm** forms the muscles, cartilage, bones, and blood vessels of the branchial arches. - It does not contribute to the formation of the nervous tissue or nerves. *Endoderm* - **Endoderm** lines the pharyngeal pouches and forms glandular structures (thymus, parathyroid). - It has no role in nerve formation.
Question 1099: Which of the following muscles is derived from the first pharyngeal arch?
- A. Stapedius
- B. Masseter (Correct Answer)
- C. Posterior belly of digastric
- D. Stylopharyngeus
Explanation: ***Masseter*** - The **masseter** is one of the four **muscles of mastication** derived from the **first pharyngeal arch** mesoderm. - All muscles of mastication (masseter, temporalis, medial pterygoid, lateral pterygoid) develop from the first arch. - The masseter is innervated by the **masseteric nerve**, a branch of the **mandibular division of CN V (CN V3)**, which is the nerve of the first pharyngeal arch. *Stapedius* - The stapedius muscle is derived from the **second pharyngeal arch**, not the first. - It is the smallest skeletal muscle in the body and dampens sound vibrations in the middle ear. - Innervated by the **facial nerve (CN VII)**, which is the nerve of the second pharyngeal arch. *Stylopharyngeus* - The stylopharyngeus is derived from the **third pharyngeal arch**. - It elevates the pharynx and larynx during swallowing. - Innervated by the **glossopharyngeal nerve (CN IX)**, which is the nerve of the third pharyngeal arch. *Posterior belly of digastric* - The posterior belly of the digastric muscle is derived from the **second pharyngeal arch**. - It assists in depressing the mandible and elevating the hyoid bone. - Innervated by the **facial nerve (CN VII)**, the nerve of the second arch, distinguishing it from the anterior belly which is first arch.
Question 1100: Ureteric bud develops from:
- A. Mesonephros (Correct Answer)
- B. Metanephros
- C. Pronephros
- D. Genital sinus
Explanation: ***Mesonephros*** - The **ureteric bud** arises as an outgrowth of the **mesonephric duct** (Wolffian duct), which is the duct of the mesonephros. - The ureteric bud emerges from the **caudal portion of the mesonephric duct** near its entry into the cloaca around the 5th week of development. - It plays a crucial role in forming the **collecting system of the kidney**, including the ureter, renal pelvis, major and minor calyces, and collecting ducts. - **Note:** While technically the ureteric bud arises from the mesonephric duct (not the mesonephric tubules), "mesonephros" is accepted as the answer referring to the mesonephric duct system. *Metanephros* - The **metanephric mesoderm** (metanephric blastema) is induced by the ureteric bud to form the **definitive kidney**. - The metanephros forms the **nephrons** (from Bowman's capsule to distal convoluted tubule). - It does not give rise to the ureteric bud; rather, it interacts with it through **reciprocal induction**. *Pronephros* - The **pronephros** is the first, transient, and **non-functional** kidney structure in human embryonic development. - It appears in the **cervical region** around week 4 and completely **regresses** by week 5. - It does not contribute to the formation of the ureteric bud or the adult kidney. *Genital sinus* - The **urogenital sinus** is derived from the ventral part of the cloaca after division by the urorectal septum. - It gives rise to the **bladder**, parts of the urethra, and contributes to external genitalia. - It is not involved in the development of the ureteric bud or the kidney's collecting system.
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