Embryology and Development — MCQs

Embryology and Development Indian Medical PG Practice Questions and MCQs

Question 651: Which of the following structures is derived from the second pharyngeal arch?

A. Sphenomandibular ligament
B. Stylomandibular ligament
C. Anterior ligament of malleus
D. Stylohyoid ligament (Correct Answer)

Explanation: The pharyngeal (branchial) arches are a high-yield topic for NEET-PG, as each arch gives rise to specific skeletal, muscular, and neural structures. ### **Explanation of the Correct Answer** The **second pharyngeal arch (Reichert’s arch)** is associated with the **facial nerve (CN VII)**. Its skeletal derivatives are formed from the cartilage of the second arch, which includes: * The **Stapes** (ear ossicle) * The **Styloid process** of the temporal bone * The **Stylohyoid ligament** (Correct Answer) * The **Lesser cornu** and **upper part of the body** of the hyoid bone. ### **Analysis of Incorrect Options** * **A & C (Sphenomandibular ligament and Anterior ligament of malleus):** These are derivatives of the **first pharyngeal arch (Meckel’s cartilage)**. The first arch also gives rise to the malleus, incus, and the mandible (via membrane bone formation around Meckel's cartilage). * **B (Stylomandibular ligament):** This is a thickening of the **deep cervical fascia** (specifically the parotid fascia) and is not a direct derivative of the pharyngeal arch cartilages. ### **NEET-PG High-Yield Pearls** * **Mnemonic for 2nd Arch:** Remember the **"S"** structures: **S**tapes, **S**tyloid process, **S**tylohyoid ligament, **S**tylohyoid muscle, and **S**even (CN VII). * **Hyoid Bone Origin:** It is unique because it comes from two arches. The **upper** part (lesser cornu) is from the **2nd arch**, while the **lower** part (greater cornu) is from the **3rd arch**. * **Muscles of 2nd Arch:** Muscles of facial expression, Stapedius, Stylohyoid, and the posterior belly of Digastric.

Question 652: Embryologically, the dorsal aorta forms which of the following structures?

A. Ascending aorta
B. Descending aorta (Correct Answer)
C. Common carotid artery
D. Pulmonary trunk

Explanation: The development of the great vessels involves a complex remodeling of the aortic arches and the primitive dorsal aortae. **1. Why the Correct Answer is Right:** The **Descending Aorta** is derived from the fusion of the two **primitive dorsal aortae** (distal to the 4th aortic arch) and the left dorsal aorta [2]. Specifically, the left dorsal aorta persists to form the descending thoracic aorta, while the right dorsal aorta normally disappears below the level of the 7th intersegmental artery. **2. Why the Incorrect Options are Wrong:** * **A. Ascending Aorta:** This develops from the **truncus arteriosus** (specifically the aortic sac) after it is partitioned by the aorticopulmonary septum [2]. * **C. Common Carotid Artery:** This is derived from the **3rd aortic arch**. * **D. Pulmonary Trunk:** Like the ascending aorta, this develops from the **truncus arteriosus** following its division by the spiral septum [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **4th Aortic Arch:** The Left forms the **Arch of Aorta** (between the left common carotid and left subclavian); the Right forms the **proximal part of the Right Subclavian Artery**. * **6th Aortic Arch:** The Left forms the **Left Pulmonary Artery and Ductus Arteriosus**; the Right forms the **Right Pulmonary Artery**. * **Recurrent Laryngeal Nerve:** The right nerve hooks around the 4th arch (Right Subclavian), while the left nerve hooks around the 6th arch (Ductus Arteriosus/Ligamentum arteriosum), explaining their asymmetrical clinical courses [1]. * **Coarctation of the Aorta:** Usually occurs distal to the origin of the left subclavian artery, at the site of the ductus arteriosus.

Question 653: Which of the following structures is NOT derived from the second pharyngeal arch?

A. Posterior belly of digastric
B. Anterior belly of digastric (Correct Answer)
C. Buccinator
D. Platysma

Explanation: The pharyngeal (branchial) arches are a high-yield topic in NEET-PG, as each arch has a specific nerve, muscle group, and skeletal derivative. ### **Explanation** The **Anterior belly of the digastric** is derived from the **First Pharyngeal Arch** (Mandibular arch). It is supplied by the nerve of the first arch, the **Mandibular nerve (V3)**, specifically via the nerve to the mylohyoid. The **Second Pharyngeal Arch** (Hyoid arch) is associated with the **Facial nerve (CN VII)**. All muscles derived from this arch are supplied by the facial nerve. ### **Analysis of Options** * **A. Posterior belly of digastric:** Derived from the **2nd arch**. Unlike the anterior belly, it is supplied by the facial nerve. This dual innervation of the digastric muscle is a classic exam favorite. * **C. Buccinator:** This is a muscle of facial expression. All muscles of facial expression originate from the **2nd arch** and are supplied by CN VII. * **D. Platysma:** Also a muscle of facial expression (located in the neck), it originates from the **2nd arch** and is supplied by the cervical branch of the facial nerve. ### **High-Yield NEET-PG Pearls** * **The "Rule of S" for 2nd Arch:** **S**tapes, **S**tyloid process, **S**tylohyoid ligament, **S**maller cornu of hyoid, **S**tapedius, and **S**eventh Cranial Nerve. * **Digastric Innervation:** Anterior belly = CN V3 (1st arch); Posterior belly = CN VII (2nd arch). * **Mnemonic for 1st Arch Muscles:** **M**uscles of **M**astication, **M**ylohyoid, Anterior belly of digastric, **T**ensor tympani, and **T**ensor veli palatini (The "M's and T's").

Question 654: The corneal stroma is derived from which embryonic tissue?

A. Paraxial mesoderm
B. Intermediate mesoderm
C. Neural crest (Correct Answer)
D. Ectoderm

Explanation: The development of the eye involves a complex interaction between the neuroectoderm, surface ectoderm, and mesenchyme (derived from both mesoderm and neural crest cells). **Why Neural Crest is Correct:** The **corneal stroma** and the **corneal endothelium** are derived from **neural crest cells**. During development, after the lens vesicle detaches from the surface ectoderm, neural crest-derived mesenchyme migrates in waves between the surface ectoderm and the lens. The first wave forms the corneal endothelium, and the second wave forms the thick, collagenous corneal stroma. **Why Other Options are Incorrect:** * **Paraxial Mesoderm:** While it contributes to the extraocular muscles and the sclera (partially), it does not form the corneal stroma. * **Intermediate Mesoderm:** This tissue primarily gives rise to the urogenital system (kidneys and gonads) and has no role in ocular development. * **Ectoderm (Surface Ectoderm):** This gives rise to the **corneal epithelium**, the lens, and the lacrimal apparatus. It is a common distractor; remember that the epithelium is ectodermal, but the deeper stroma is neural crest-derived. **High-Yield Clinical Pearls for NEET-PG:** * **Corneal Layers Origin:** Epithelium = Surface Ectoderm; Stroma/Endothelium = Neural Crest. * **Neural Crest Derivatives in Eye:** Sclera (most of it), Choroid, Ciliary muscle, Iris stroma, and the Trabecular meshwork. * **Neuroectoderm Derivatives:** Retina, Iris epithelium, and Optic nerve. * **Key Concept:** If a question asks about the "mesenchyme" of the head and neck, it is almost always referring to **Ectomesenchyme** (Neural Crest).

Question 655: Which umbilical vessel disappears by the 4th month of gestation?

A. Right umbilical artery
B. Left umbilical artery
C. Right umbilical vein (Correct Answer)
D. Left umbilical vein

Explanation: ### Explanation In early embryonic development, there are initially two umbilical arteries and two umbilical veins. The **Right Umbilical Vein** undergoes regression and completely disappears by the **4th month (late in the first trimester)** of gestation. **1. Why the Right Umbilical Vein is correct:** Initially, both right and left umbilical veins carry oxygenated blood from the placenta to the sinus venosus. However, as the liver develops, the umbilical veins lose their direct connection to the heart and form a plexus within the liver. The right umbilical vein eventually obliterates, leaving the **Left Umbilical Vein** as the sole vessel responsible for carrying oxygenated blood from the placenta to the fetus. **2. Analysis of Incorrect Options:** * **Right and Left Umbilical Arteries (Options A & B):** Both umbilical arteries persist throughout the entire intrauterine life [3]. They carry deoxygenated blood from the fetus to the placenta. After birth, they obliterate to form the **medial umbilical ligaments** [3]. * **Left Umbilical Vein (Option D):** This vessel does not disappear during gestation [1]. It persists until birth, after which it obliterates to form the **ligamentum teres hepatis** (found in the free margin of the falciform ligament) [1], [3]. ### High-Yield Clinical Pearls for NEET-PG: * **Rule of "Left is Last":** Remember that the **Left** umbilical vein is the one that stays (until birth), while the **Right** disappears early. * **The 3-Vessel Cord:** A normal umbilical cord contains **two arteries and one (left) vein** [2]. * **Single Umbilical Artery (SUA):** This is a significant clinical finding often associated with congenital anomalies, particularly renal and cardiac malformations. * **Ductus Venosus:** A shunt that allows oxygenated blood from the left umbilical vein to bypass the liver capillaries and enter the IVC directly [1]. It becomes the **ligamentum venosum** after birth [3].

Question 656: All of the following statements regarding the development of the thyroid gland are true, EXCEPT:

A. Its development begins at the 3rd week of gestation.
B. It develops from the floor of the primitive pharynx.
C. An ectopic location of the thyroid gland is at the base of the tongue.
D. Thyroid hormone synthesis begins at the 20th week of gestation. (Correct Answer)

Explanation: ### Explanation The thyroid gland is the first endocrine gland to develop in the embryo. Understanding its timeline and anatomical descent is high-yield for NEET-PG. **Why Option D is the Correct Answer (The False Statement):** Thyroid hormone synthesis (iodine trapping and colloid formation) begins much earlier than the 20th week. It typically starts at the **10th to 12th week** of gestation [2]. By the end of the first trimester, the gland is functionally active and capable of producing T4 [2]. **Analysis of Other Options:** * **Option A:** Development begins around the **24th day (3rd week)** of gestation as a median endodermal thickening. * **Option B:** It originates from the **floor of the primitive pharynx** [1], specifically at the site of the **foramen cecum**, located between the tuberculum impar and the copula. * **Option C:** The gland descends via the thyroglossal duct [1]. Failure of descent leads to **Lingual Thyroid**, the most common site for ectopic thyroid tissue, located at the base of the tongue [2]. **High-Yield Clinical Pearls:** 1. **Thyroglossal Duct Cyst:** A remnant of the descent path; it typically presents as a midline neck swelling that **moves upward on protrusion of the tongue** [2]. 2. **Pyramidal Lobe:** A common anatomical variant representing a persistent distal end of the thyroglossal duct [1]. 3. **Parafollicular (C) Cells:** Unlike the follicular cells (endoderm), these cells (secreting calcitonin) are derived from the **Ultimobranchial body** (4th/5th pharyngeal pouch via neural crest cells).

Question 657: Which of the following events occurs during the third week of human embryo development?

A. Neural plate formation stimulated by the notochord.
B. Formation of the amniotic disc.
C. The body stalk moves ventrally to form the umbilical cord.
D. Formation of the primitive streak. (Correct Answer)

Explanation: **Explanation:** The **third week of development** is characterized by the process of **Gastrulation**, which converts the bilaminar disc into a trilaminar embryonic disc (ectoderm, mesoderm, and endoderm). 1. **Why Option D is Correct:** The **primitive streak** is the first sign of gastrulation. It appears at the beginning of the third week (Day 15) on the dorsal surface of the epiblast. It establishes the cranio-caudal axis and the bilateral symmetry of the embryo. 2. **Why Other Options are Incorrect:** * **Option A:** While the notochord does induce the overlying ectoderm to form the **neural plate**, this process (Neurulation) typically occurs in the **late third week into the fourth week**. The primitive streak must form first to allow the migration of cells that form the notochord. * **Option B:** The **amniotic cavity** [1] and the bilaminar disc (epiblast and hypoblast) [1] are hallmarks of the **second week** ("Week of Twos"). * **Option C:** The ventral movement of the body stalk and the formation of the definitive **umbilical cord** occur during the **fourth to eighth weeks** as a result of embryonic folding (cephalocaudal and lateral folding) [1]. **High-Yield NEET-PG Pearls:** * **Gastrulation:** The "Rule of Threes" applies to the 3rd week—3 germ layers form from the primitive streak. * **Remnants:** If the primitive streak fails to regress, it can lead to **Sacrococcygeal Teratoma** (the most common tumor in newborns). * **Prechordal Plate:** This is the future site of the oropharyngeal membrane and acts as an important signaling center for forebrain development.

Question 658: Formation of the primary palate is from which of the following structures?

A. Lateral nasal prominences
B. Medial nasal prominences (Correct Answer)
C. Maxillary prominences
D. Mandibular prominences

Explanation: ### Explanation The development of the face and palate occurs between the 4th and 10th weeks of gestation, involving the fusion of five facial primordia. **Why the Medial Nasal Prominences are Correct:** The **primary palate** (also known as the premaxilla) is formed by the fusion of the two **medial nasal prominences** in the midline. This fusion creates the **intermaxillary segment**, which gives rise to three components: 1. The philtrum of the upper lip. 2. The premaxillary part of the maxilla (carrying the four incisor teeth). 3. The triangular **primary palate**. **Analysis of Incorrect Options:** * **A. Lateral nasal prominences:** These form the alae (sides) of the nose. They do not contribute to the palate. * **C. Maxillary prominences:** These form the **secondary palate** via the development of palatal shelves. While they fuse with the intermaxillary segment, they are not the primary source of the primary palate itself. * **D. Mandibular prominences:** These fuse in the midline to form the lower jaw, lower lip, and the lower part of the face. **High-Yield Clinical Pearls for NEET-PG:** * **Secondary Palate:** Formed by the fusion of **lateral palatine shelves** (outgrowths of the maxillary prominences). * **Cleft Lip:** Results from the failure of the **maxillary prominence** to fuse with the **medial nasal prominence**. * **Cleft Palate:** Results from the failure of the palatine shelves to fuse with each other or with the primary palate [1]. * **Incisive Foramen:** This serves as the developmental landmark separating the primary and secondary palates. * **Stomodeum:** The primitive mouth, separated from the pharynx by the buccopharyngeal membrane.

Question 659: The structure marked by the blue arrow develops from which of the following structures?

A. Septum primum
B. Endocardial cushion (Correct Answer)
C. Conus
D. Bulboventricular cavity

Explanation: ***Endocardial cushion*** - The **endocardial cushions** give rise to the **atrioventricular (AV) valves** (mitral and tricuspid) and the **membranous portions** of both the interventricular and interatrial septa. - These structures are crucial for proper **cardiac septation** and valve formation during embryonic development. *Septum primum* - Forms the **primary atrial septum** that initially separates the left and right atria during cardiac development. - Does not contribute to **AV valve formation** but rather to atrial septation and the **foramen ovale**. *Conus* - Develops into the **outflow tracts** of both ventricles, including the **aortic and pulmonary valve cusps**. - Contributes to the **membranous interventricular septum** but not to AV valve structures. *Bulboventricular cavity* - Represents the **primitive ventricular chamber** that eventually forms the main ventricular cavities. - Does not directly contribute to **valve formation** or septal structures marked by the arrow.

Question 660: The embryonic period is defined as the time from fertilization until which week of development?

A. The end of the first week
B. The end of the third week
C. The end of the eighth week (Correct Answer)
D. The end of the twelfth week

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The prenatal development of a human is divided into two main stages: the **embryonic period** and the **fetal period**. The embryonic period begins at fertilization [1] and lasts until the **end of the 8th week** (56 days) of gestation [2]. This stage is characterized by **organogenesis**—the formation of all major organ systems and the basic human body plan. By the end of this period, the embryo has a distinctly human appearance. **2. Analysis of Incorrect Options:** * **Option A (End of the first week):** This marks the completion of implantation and the formation of the blastocyst [1]. * **Option B (End of the third week):** This is the period of **gastrulation** (formation of the three germ layers: ectoderm, mesoderm, and endoderm). While organogenesis begins here, it is not the end of the embryonic period. * **Option C (End of the twelfth week):** This marks the end of the **first trimester**. By this time, the fetal period is well underway, and the focus has shifted from organ formation to growth and maturation. **3. NEET-PG High-Yield Clinical Pearls:** * **Teratogenicity:** The embryonic period (Weeks 3–8) is the **most critical period** for development. Exposure to teratogens (e.g., Thalidomide, Alcohol, TORCH infections) during this window carries the highest risk of major structural congenital anomalies [2]. * **Fetal Period:** Starts from the **9th week** until birth [2]. It is primarily characterized by rapid body growth and functional maturation of tissues. * **Rule of 2s:** Occurs in the 2nd week (2 germ layers: epiblast/hypoblast; 2 cavities: amniotic/yolk sac) [3]. * **Rule of 3s:** Occurs in the 3rd week (3 germ layers via gastrulation).

Practice by Chapter

Gametogenesis and Fertilization

Practice Questions

Early Embryonic Development

Practice Questions

Placentation

Practice Questions

Development of Nervous System

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Development of Cardiovascular System

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Development of Gastrointestinal System

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Development of Urogenital System

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Development of Musculoskeletal System

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Development of Head and Neck

Practice Questions

Congenital Anomalies

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Teratology

Practice Questions

Molecular Mechanisms in Development

Practice Questions

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