Chapter: Embryology; Topic: Germ Layer Derivatives; Subtopic: Neural Crest Cell Derivatives
Keyword Definitions:
Glomus Cells: Specialized neuroendocrine cells found in carotid and aortic bodies that help regulate blood oxygen levels.
Neural Crest: A transient embryonic structure giving rise to diverse cell types including melanocytes, cranial cartilage, and adrenal medulla cells.
Germ Layers: Three primary layers in embryonic development — ectoderm, mesoderm, and endoderm — from which all tissues originate.
Neuroectoderm: Portion of ectoderm that differentiates into the nervous system and related structures.
Mesoderm: Middle germ layer forming muscles, bones, and blood vessels.
Lead Question - 2014
Glomus cells are derived from?
a) Surface ectoderm
b) Neuroectoderm
c) Mesoderm
d) Endoderm
Explanation: Glomus cells, also called chemoreceptor cells, originate from the neural crest (derived from ectoderm). They are neuroendocrine in nature and are present in the carotid and aortic bodies. These cells sense changes in blood oxygen and carbon dioxide levels and help regulate respiratory activity. Hence, the correct answer is neuroectoderm.
1) Adrenal medulla is derived from?
a) Neural crest
b) Neural tube
c) Mesoderm
d) Endoderm
Explanation: The adrenal medulla arises from neural crest cells, which migrate to the developing adrenal gland and differentiate into chromaffin cells. These cells secrete catecholamines (epinephrine and norepinephrine) that mediate the body’s stress response. The adrenal cortex, however, develops from mesodermal origin. Thus, the answer is neural crest.
2) Parafollicular cells of thyroid develop from?
a) Endoderm
b) Mesoderm
c) Neural crest
d) Surface ectoderm
Explanation: Parafollicular or C cells of the thyroid originate from the neural crest via the ultimobranchial body (a derivative of the 4th pharyngeal pouch). These cells secrete calcitonin, which reduces blood calcium levels by inhibiting bone resorption. The thyroid follicular cells arise from endoderm. Hence, answer: neural crest.
3) Melanocytes of the skin are derived from?
a) Surface ectoderm
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Melanocytes are pigment-producing cells derived from neural crest cells. They migrate into the epidermis, hair follicles, and uveal tract of the eye. Melanocytes synthesize melanin, which protects against ultraviolet radiation. The rest of the epidermis develops from surface ectoderm. Thus, the correct answer is neural crest.
4) Schwann cells originate from?
a) Neural tube
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Schwann cells originate from neural crest cells and are responsible for the myelination of peripheral nerves. They play a vital role in nerve regeneration after injury. Oligodendrocytes, which myelinate the central nervous system, are derived from neuroectoderm. Hence, the correct answer is neural crest.
5) Which of the following structures arises from surface ectoderm?
a) Retina
b) Lens of eye
c) Pituitary gland (posterior lobe)
d) Cerebrum
Explanation: The lens of the eye is derived from surface ectoderm, which invaginates to form the lens vesicle. The retina and posterior pituitary originate from neuroectoderm, and the cerebrum from neural tube. Surface ectoderm also forms epidermis, hair, and nails. Thus, the answer is lens of eye.
6) A 2-year-old child with congenital absence of adrenal medulla likely has a defect in which embryonic structure?
a) Neural crest
b) Neural tube
c) Mesoderm
d) Endoderm
Explanation: Adrenal medulla originates from neural crest cells, which differentiate into chromaffin cells. Defective migration of these cells can result in congenital absence or hypoplasia of adrenal medulla. This causes reduced catecholamine secretion and poor stress response. Thus, the defect is in neural crest origin.
7) A patient with albinism has normal number of melanocytes but lacks melanin. The embryonic origin of affected cells is?
a) Neural crest
b) Surface ectoderm
c) Mesoderm
d) Endoderm
Explanation: In albinism, melanocytes (derived from neural crest) are normal in number but have defective melanin synthesis due to enzyme deficiency (tyrosinase). The pigmentation defect is biochemical, not structural. The embryologic origin of these cells remains neural crest.
8) Tumor of carotid body (chemodectoma) arises from cells derived from?
a) Neural tube
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Chemodectoma or paraganglioma of the carotid body arises from neural crest-derived glomus cells. These cells function as chemoreceptors. Their hyperplasia or neoplasia can result in nonchromaffin paragangliomas, showing neuroendocrine differentiation. Hence, origin is neural crest.
9) A patient with congenital Hirschsprung disease lacks enteric ganglia. This defect is due to abnormal migration of?
a) Neural tube cells
b) Neural crest cells
c) Mesodermal cells
d) Endodermal cells
Explanation: Hirschsprung disease results from failed migration of neural crest cells to the distal gut, leading to absence of enteric ganglion cells in the myenteric and submucosal plexuses. This causes functional obstruction and megacolon. Thus, the embryonic defect involves neural crest cells.
10) Pheochromocytoma arises from which embryonic derivative?
a) Neural tube
b) Neural crest
c) Mesoderm
d) Endoderm
Explanation: Pheochromocytoma is a tumor of adrenal medulla chromaffin cells derived from the neural crest. These cells secrete catecholamines. The tumor causes episodic hypertension, sweating, and palpitations. Neural crest cells contribute to the sympathetic chain and paraganglia. Hence, the correct answer is neural crest.
Chapter: Embryology; Topic: Development of Genital System; Subtopic: Origin of Female Genital Tract
Keyword Definitions:
Vagina: The muscular canal connecting the uterus to the external genitalia, serving as a passage for menstrual flow and childbirth.
Epithelium: A layer of cells forming the surface of the body or lining internal organs and cavities.
Müllerian Duct: Also called paramesonephric duct, it gives rise to female reproductive organs like the uterus, fallopian tubes, and upper vagina.
Urogenital Sinus: An embryonic structure contributing to the lower vagina and urethra.
Mesonephric Duct (Wolffian Duct): A structure primarily involved in the development of male reproductive organs.
Lead Question - 2014
Epithelium of vagina arises from?
a) Ectoderm
b) Wolffian duct
c) Mesoderm
d) Mesonephric duct
Explanation: The upper one-third of the vagina is derived from the Müllerian duct (paramesonephric duct), while the lower two-thirds develop from the urogenital sinus, whose lining is of endodermal origin. The vaginal epithelium, therefore, arises mainly from endoderm (urogenital sinus contribution). The connective tissue and muscle of the vagina are mesodermal in origin. Correct answer: endoderm.
1) Which part of the vagina is derived from the Müllerian duct?
a) Upper one-third
b) Lower two-thirds
c) Entire vagina
d) None
Explanation: The upper one-third of the vagina arises from the Müllerian (paramesonephric) ducts, while the lower two-thirds originate from the urogenital sinus. The junction between these two developmental origins is marked histologically by a transitional zone. Hence, the correct answer is upper one-third derived from Müllerian duct.
2) The lower two-thirds of the vagina develop from?
a) Paramesonephric duct
b) Urogenital sinus
c) Mesonephric duct
d) Cloaca
Explanation: The urogenital sinus (endodermal origin) gives rise to the lower two-thirds of the vagina. It joins the descending Müllerian ducts to form the vaginal plate, which canalizes later to form the vagina. Hence, the correct answer is urogenital sinus.
3) Which embryonic layer gives rise to vaginal epithelium?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neuroectoderm
Explanation: Vaginal epithelium is mainly derived from the endoderm of the urogenital sinus. The mesoderm contributes to the muscular and connective tissue layers, while the Müllerian duct contributes structurally to the upper vagina. Thus, epithelial origin is endodermal. Correct answer: endoderm.
4) In a female newborn with vaginal agenesis, which embryonic structure failed to develop?
a) Müllerian duct
b) Urogenital sinus
c) Cloacal membrane
d) Mesonephric duct
Explanation: Vaginal agenesis occurs when there is defective development of the urogenital sinus or Müllerian ducts. If both fail to fuse or canalize properly, the vagina is absent or rudimentary. Thus, failure of urogenital sinus development leads to lower vaginal agenesis. Correct answer: urogenital sinus.
5) The epithelium of uterus is derived from?
a) Mesoderm
b) Endoderm
c) Ectoderm
d) Neural crest
Explanation: The uterus, fallopian tubes, and upper vagina develop from the paramesonephric (Müllerian) ducts, which are mesodermal in origin. Hence, uterine epithelium arises from mesoderm. This distinguishes it from vaginal epithelium, which arises mainly from endoderm. Correct answer: mesoderm.
6) A 16-year-old girl presents with primary amenorrhea and normal secondary sexual characteristics. Ultrasound shows absence of vagina and uterus. Likely diagnosis?
a) Androgen insensitivity syndrome
b) Müllerian agenesis
c) Turner's syndrome
d) Congenital adrenal hyperplasia
Explanation: In Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome), the Müllerian ducts fail to develop, leading to absence of uterus and upper vagina. Ovaries are normal, hence secondary sexual features are present. Thus, the correct diagnosis is Müllerian agenesis.
7) A female patient with cloacal anomaly shows abnormal connection between vagina and rectum. This defect arises due to failure of?
a) Urorectal septum formation
b) Müllerian duct fusion
c) Cloacal membrane rupture
d) Mesonephric duct regression
Explanation: Cloacal anomalies occur when the urorectal septum fails to divide the cloaca into urogenital and anorectal parts. This leads to abnormal communication between the vagina, urethra, and rectum. Correct answer: urorectal septum formation.
8) The hymen represents the remains of?
a) Cloacal membrane
b) Urogenital sinus
c) Müllerian duct
d) Mesonephric duct
Explanation: The hymen marks the junction between the vagina (from urogenital sinus) and vestibule (from ectoderm). It is a remnant of the cloacal membrane that persists at the vaginal opening. It ruptures during first intercourse or tampon use. Correct answer: cloacal membrane.
9) In a female fetus, the urogenital sinus contributes to which of the following?
a) Lower part of vagina
b) Fallopian tubes
c) Uterus
d) Ovary
Explanation: The urogenital sinus forms the lower two-thirds of the vagina and the vestibule. It does not form the uterus or fallopian tubes, which arise from Müllerian ducts. Hence, the correct answer is lower part of vagina.
10) A newborn girl has a blind vaginal pouch but normal ovaries. The likely cause is?
a) Absence of urogenital sinus contribution
b) Absence of Müllerian duct development
c) Absence of mesonephric duct
d) Defective cloacal membrane
Explanation: A blind vaginal pouch occurs when the Müllerian ducts fail to develop but the urogenital sinus is present. The ovaries (gonadal origin) are unaffected as they arise from the genital ridge. This condition is seen in Müllerian agenesis (MRKH syndrome). Correct answer: absence of Müllerian duct development.
Chapter: Embryology; Topic: Development of Face and Pharyngeal Arches; Subtopic: Derivatives of the First Pharyngeal Arch
Keyword Definitions:
Pharyngeal Arches: Series of mesodermal outpouchings in the embryonic head region that give rise to various structures in the face, neck, and pharynx.
First Pharyngeal Arch: Also known as the mandibular arch, it contributes to the formation of the maxilla, mandible, malleus, and muscles of mastication.
Maxillary Process: Part of the first arch that forms the upper jaw, lateral part of the upper lip, and part of the palate.
Mandibular Process: Part of the first arch that forms the lower jaw and lower lip.
Frontonasal Process: A separate embryonic prominence that gives rise to the forehead, nose, and philtrum of the upper lip.
Lead Question - 2014
Which of the following is derived from Ist arch?
a) Frontonasal process
b) Maxillary process
c) Mandibular process
d) Both maxillary & mandibular processes
Explanation: The first pharyngeal arch divides into two processes — the maxillary process and the mandibular process. These contribute to the development of the upper and lower jaws, muscles of mastication, and part of the ear ossicles. The frontonasal process is not derived from this arch but from neural crest mesenchyme. Correct answer: Both maxillary & mandibular processes.
1) Which nerve is associated with the first pharyngeal arch?
a) Facial nerve
b) Mandibular nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The nerve of the first pharyngeal arch is the mandibular division of the trigeminal nerve (CN V3). It supplies the muscles derived from this arch, such as the muscles of mastication, mylohyoid, tensor tympani, and tensor veli palatini. Correct answer: Mandibular nerve.
2) Which muscle develops from the first pharyngeal arch?
a) Orbicularis oculi
b) Masseter
c) Stylopharyngeus
d) Cricothyroid
Explanation: The masseter, along with other muscles of mastication (temporalis, medial and lateral pterygoid), develops from the first pharyngeal arch. These muscles are supplied by the mandibular nerve. Other options arise from different arches. Correct answer: Masseter.
3) Which bones are derivatives of Meckel’s cartilage?
a) Malleus and incus
b) Stapes and styloid process
c) Hyoid bone
d) Clavicle
Explanation: The Meckel’s cartilage arises from the first pharyngeal arch and gives rise to the malleus and incus of the middle ear, along with part of the mandible. Stapes and styloid process belong to the second arch. Correct answer: Malleus and incus.
4) A newborn has micrognathia (small jaw) and cleft palate. The most likely developmental defect involves?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation: Defective development of the first pharyngeal arch leads to mandibular and maxillary hypoplasia, resulting in micrognathia and facial deformities as seen in Pierre Robin sequence. Thus, the correct answer is first pharyngeal arch.
5) The anterior two-thirds of the tongue is derived from which arch?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The anterior two-thirds of the tongue develops from the first pharyngeal arch (lateral lingual swellings). Sensory supply is via the mandibular nerve, and taste supply is by the chorda tympani (from second arch). Correct answer: First arch.
6) A child presents with mandibulofacial dysostosis (Treacher Collins syndrome). The defect lies in?
a) Neural crest cells of first arch
b) Mesoderm of second arch
c) Endoderm of third pouch
d) Mesenchyme of fourth arch
Explanation: Treacher Collins syndrome results from defective migration of neural crest cells into the first pharyngeal arch, leading to underdeveloped zygomatic and mandibular structures. Thus, the correct answer is Neural crest cells of first arch.
7) The maxillary prominence contributes to the formation of?
a) Upper lip and cheeks
b) Lower jaw
c) Nose
d) Forehead
Explanation: The maxillary process forms the upper lip (excluding philtrum) and the lateral portions of the face such as the cheeks. It fuses with the medial nasal process to complete the upper lip formation. Correct answer: Upper lip and cheeks.
8) A newborn with cleft lip has failure of fusion between?
a) Maxillary and medial nasal processes
b) Lateral nasal and maxillary processes
c) Mandibular and hyoid arches
d) Frontonasal and mandibular processes
Explanation: A cleft lip results from failure of fusion between the maxillary process and the medial nasal process. This leads to a gap in the upper lip on one or both sides. Correct answer: Maxillary and medial nasal processes.
9) The mandibular process gives rise to?
a) Lower jaw and lower lip
b) Upper jaw and cheeks
c) Nose and philtrum
d) Forehead and scalp
Explanation: The mandibular process, a derivative of the first pharyngeal arch, forms the lower jaw, lower lip, and associated structures. It fuses in the midline to form the mandibular symphysis. Correct answer: Lower jaw and lower lip.
10) A neonate presents with malformed ear ossicles and difficulty in feeding. The likely embryological defect involves?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal pouch
d) Fourth pharyngeal arch
Explanation: The first pharyngeal arch contributes to the formation of malleus and incus, as well as muscles of mastication. Defects in this arch can cause malformation of ear ossicles and feeding problems. Correct answer: First pharyngeal arch.
Keyword Definitions:
Pharyngeal arches: Embryonic structures that contribute to the development of head and neck components.
First arch (Mandibular arch): Gives rise to maxilla, mandible, malleus, and incus.
Meckel’s cartilage: Cartilaginous bar of the first arch that forms part of the middle ear and mandible.
Derivatives: The structures (bones, muscles, nerves) developed from specific embryological origins.
Lead Question - 2014
Skeletal derivative of Ist arch ?
a) Stapes
b) Hyoid
c) Maxilla
d) Laryngeal cartilages
Explanation: The first pharyngeal arch, also known as the mandibular arch, gives rise to skeletal structures including the maxilla, mandible, malleus, and incus. These are derived from Meckel’s cartilage and mesenchymal condensations around it. Stapes arises from the second arch, and hyoid from second and third arches. Hence, the correct answer is Maxilla.
Guessed Questions:
1) Which nerve supplies muscles derived from the first pharyngeal arch?
a) Facial nerve
b) Trigeminal nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The muscles of mastication, derived from the first pharyngeal arch, are supplied by the mandibular division of the trigeminal nerve (V3). This arch also gives rise to the mylohyoid and tensor tympani muscles. Hence, the correct answer is Trigeminal nerve.
2) Meckel’s cartilage forms which of the following?
a) Stapes
b) Malleus and incus
c) Styloid process
d) Thyroid cartilage
Explanation: Meckel’s cartilage, the cartilaginous component of the first arch, forms the malleus and incus of the middle ear. It also contributes to the sphenomandibular ligament. Other options like stapes or styloid process belong to the second arch. Hence, the correct answer is Malleus and incus.
3) Which artery represents the derivative of the first arch?
a) Maxillary artery
b) Facial artery
c) External carotid artery
d) Lingual artery
Explanation: The artery of the first pharyngeal arch contributes to the formation of the maxillary artery in the adult. The maxillary artery supplies deep structures of the face, derived from the same embryonic arch. Hence, the correct answer is Maxillary artery.
4) Which of the following muscles are derived from the first arch?
a) Stylopharyngeus
b) Muscles of mastication
c) Pharyngeal constrictors
d) Laryngeal muscles
Explanation: Muscles of mastication (masseter, temporalis, medial and lateral pterygoids) are derived from the first arch mesoderm and innervated by mandibular nerve (V3). Stylopharyngeus comes from the third arch. Hence, the correct answer is Muscles of mastication.
5) Which pharyngeal arch anomaly causes mandibulofacial dysostosis?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: Mandibulofacial dysostosis (Treacher-Collins syndrome) results from defective neural crest cell migration into the first pharyngeal arch. This leads to hypoplasia of the zygomatic bone and mandible. Hence, the correct answer is First arch.
6) A child presents with underdeveloped mandible and malformed ears. Which embryological structure is most likely defective?
a) Second pharyngeal arch
b) First pharyngeal arch
c) Third pharyngeal pouch
d) Fourth pharyngeal arch
Explanation: The first pharyngeal arch contributes to formation of the mandible and external ear structures. Defective migration or development leads to micrognathia and ear anomalies. Hence, the correct answer is First pharyngeal arch.
7) The mandibular process forms which adult structure?
a) Lower jaw
b) Upper lip
c) Nasal septum
d) Palatine bone
Explanation: The mandibular process of the first arch fuses in the midline to form the lower jaw (mandible) and lower lip. Hence, the correct answer is Lower jaw.
8) Which of the following is not derived from the first arch?
a) Malleus
b) Maxilla
c) Stapes
d) Mandible
Explanation: The stapes is derived from Reichert’s cartilage of the second pharyngeal arch, whereas the malleus, incus, maxilla, and mandible arise from the first arch. Hence, the correct answer is Stapes.
9) The nerve of the first pharyngeal arch is?
a) Facial nerve
b) Trigeminal nerve
c) Glossopharyngeal nerve
d) Vagus nerve
Explanation: The first pharyngeal arch is supplied by the mandibular division of the trigeminal nerve (V3), which innervates its muscles and sensory derivatives. Hence, the correct answer is Trigeminal nerve.
10) The anterior belly of digastric muscle is derived from?
a) First pharyngeal arch
b) Second pharyngeal arch
c) Third pharyngeal arch
d) Fourth pharyngeal arch
Explanation: The anterior belly of the digastric muscle and mylohyoid are derived from the first pharyngeal arch mesoderm and supplied by the mylohyoid branch of mandibular nerve. Hence, the correct answer is First pharyngeal arch.
Keyword Definitions:
Pharyngeal arches: Embryonic structures that develop into bones, muscles, and nerves of the head and neck.
Reichert’s cartilage: The cartilaginous core of the second pharyngeal arch giving rise to stapes, styloid process, and part of hyoid bone.
Styloid process: A slender projection from the temporal bone derived from the second arch cartilage.
Facial nerve: Nerve of the second arch supplying muscles of facial expression.
Lead Question - 2014
Styloid process is derived from ?
a) 1st arch
b) 2nd arch
c) 3rd arch
d) 4th arch
Explanation: The styloid process, part of the temporal bone, develops from Reichert’s cartilage of the second pharyngeal arch. Other derivatives of this arch include the stapes, stylohyoid ligament, and lesser horn of hyoid bone. The facial nerve is the nerve of this arch. Hence, the correct answer is 2nd arch.
Guessed Questions:
1) Which nerve is associated with the second pharyngeal arch?
a) Glossopharyngeal nerve
b) Trigeminal nerve
c) Facial nerve
d) Vagus nerve
Explanation: The second pharyngeal arch, also called the hyoid arch, is innervated by the facial nerve (cranial nerve VII). It supplies all muscles derived from this arch, including muscles of facial expression and stapedius. Hence, the correct answer is Facial nerve.
2) Which of the following structures is derived from Reichert’s cartilage?
a) Malleus
b) Incus
c) Stapes
d) Mandible
Explanation: Reichert’s cartilage, the cartilage of the second pharyngeal arch, gives rise to the stapes of the middle ear, styloid process, stylohyoid ligament, and lesser horn of the hyoid. Malleus and incus are derived from the first arch. Hence, the correct answer is Stapes.
3) Which muscle is derived from the second pharyngeal arch?
a) Stylopharyngeus
b) Masseter
c) Orbicularis oculi
d) Cricothyroid
Explanation: The muscles of facial expression, including orbicularis oculi, orbicularis oris, and platysma, develop from the mesoderm of the second pharyngeal arch. These are supplied by the facial nerve. Hence, the correct answer is Orbicularis oculi.
4) The stapes bone develops from which pharyngeal arch?
a) First
b) Second
c) Third
d) Fourth
Explanation: The stapes, one of the auditory ossicles, is derived from Reichert’s cartilage of the second pharyngeal arch. The facial nerve supplies muscles related to this arch, including the stapedius muscle that attaches to the stapes. Hence, the correct answer is Second.
5) The lesser horn of the hyoid bone is derived from?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The lesser horn (cornu) and upper part of the body of the hyoid bone develop from the cartilage of the second pharyngeal arch (Reichert’s cartilage). The greater horn and lower part of the hyoid come from the third arch. Hence, the correct answer is Second arch.
6) A patient with facial nerve palsy is unable to close the eye. This nerve supplies muscles derived from which embryonic arch?
a) First
b) Second
c) Third
d) Fourth
Explanation: The facial nerve (VII) supplies the muscles of facial expression, all derived from the second pharyngeal arch. In facial nerve palsy, loss of orbicularis oculi function prevents eye closure. Hence, the correct answer is Second arch.
7) Which ligament is derived from Reichert’s cartilage?
a) Stylohyoid ligament
b) Sphenomandibular ligament
c) Cricothyroid ligament
d) Stylomandibular ligament
Explanation: The stylohyoid ligament connects the styloid process to the lesser horn of the hyoid bone and is derived from the second pharyngeal arch cartilage. Hence, the correct answer is Stylohyoid ligament.
8) Which structure forms the cartilaginous part of the second pharyngeal arch?
a) Meckel’s cartilage
b) Reichert’s cartilage
c) Thyroid cartilage
d) Arytenoid cartilage
Explanation: Reichert’s cartilage is the cartilaginous component of the second arch, forming the stapes, styloid process, stylohyoid ligament, and lesser horn of hyoid. Hence, the correct answer is Reichert’s cartilage.
9) Which pharyngeal arch contributes to the formation of muscles of facial expression?
a) First
b) Second
c) Third
d) Fourth
Explanation: The second pharyngeal arch forms muscles responsible for facial expression, including orbicularis oris, buccinator, and platysma, all supplied by the facial nerve. Hence, the correct answer is Second.
10) In a congenital anomaly, absence of the styloid process would indicate defective development of which structure?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The styloid process is a derivative of Reichert’s cartilage from the second pharyngeal arch. Its absence suggests defective differentiation of this arch. Hence, the correct answer is Second arch.
Chapter: Embryology; Topic: Pharyngeal Arches; Subtopic: Muscular Derivatives of Pharyngeal Arches
Keyword Definitions:
Pharyngeal arches: Series of embryonic structures in the head and neck that give rise to muscles, bones, and nerves.
Pharyngeal muscles: Muscles that form the wall of the pharynx and aid in swallowing.
Branchial apparatus: Collective term for pharyngeal arches, clefts, and pouches.
Mesoderm: Embryonic layer giving rise to muscles and connective tissues.
Cartilage derivatives: Skeletal elements formed from arch mesenchyme.
Lead Question – 2014
Pharyngeal muscles are derived from which pharyngeal arch?
a) 1st
b) 2nd
c) 3rd
d) 5th
Explanation:
Pharyngeal muscles mainly develop from the mesoderm of the fourth and sixth pharyngeal arches. The 4th arch gives rise to pharyngeal constrictors, cricothyroid, and levator veli palatini, while the 6th arch forms intrinsic laryngeal muscles. These arches are supplied by branches of the vagus nerve. Correct answer: Fourth arch.
1) Muscles of mastication are derived from which pharyngeal arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: The muscles of mastication originate from the first pharyngeal arch, also called the mandibular arch. These include temporalis, masseter, medial and lateral pterygoids. The mandibular division of the trigeminal nerve (CN V3) supplies them, confirming their first arch origin. Answer: 1st arch.
2) Stylopharyngeus muscle is derived from?
a) 2nd arch
b) 3rd arch
c) 4th arch
d) 6th arch
Explanation: The stylopharyngeus muscle is the only muscle derived from the third pharyngeal arch. It is supplied by the glossopharyngeal nerve (CN IX). It elevates the pharynx during swallowing, showing its embryologic connection to the third arch. Answer: 3rd arch.
3) Which nerve supplies the muscles derived from the 4th arch?
a) Glossopharyngeal
b) Facial
c) Superior laryngeal
d) Recurrent laryngeal
Explanation: The superior laryngeal branch of the vagus nerve innervates muscles from the fourth arch such as cricothyroid, pharyngeal constrictors, and levator veli palatini. This nerve also carries sensory fibers to the laryngeal mucosa above the vocal cords. Answer: Superior laryngeal nerve.
4) Facial expression muscles originate from which arch?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: Muscles of facial expression are derived from the second pharyngeal (hyoid) arch. These muscles are innervated by the facial nerve (CN VII). Examples include buccinator, orbicularis oris, and frontalis. Answer: 2nd arch.
5) Clinical Case: A patient with facial nerve palsy cannot close his eye. Which pharyngeal arch origin is affected?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: Orbicularis oculi muscle is derived from the second pharyngeal arch and is supplied by the facial nerve (CN VII). Damage leads to loss of eyelid closure and facial asymmetry. Answer: 2nd arch.
6) Clinical Case: Injury to the recurrent laryngeal nerve affects muscles derived from which arch?
a) 4th
b) 6th
c) 3rd
d) 2nd
Explanation: The recurrent laryngeal nerve supplies muscles derived from the sixth pharyngeal arch. These include intrinsic laryngeal muscles responsible for phonation. Injury leads to hoarseness and vocal cord paralysis. Answer: 6th arch.
7) Which pharyngeal arch gives rise to the mylohyoid muscle?
a) 1st
b) 2nd
c) 3rd
d) 4th
Explanation: The mylohyoid muscle originates from the first pharyngeal arch and assists in elevating the floor of the mouth during swallowing. It is supplied by the mylohyoid branch of the inferior alveolar nerve (CN V3). Answer: 1st arch.
8) Clinical Case: A child with congenital absence of pharyngeal constrictor muscles will have swallowing difficulty due to defect in?
a) 1st arch
b) 3rd arch
c) 4th arch
d) 6th arch
Explanation: Pharyngeal constrictors develop from the fourth arch. Their absence leads to dysphagia. These muscles are innervated by the pharyngeal plexus formed by the vagus nerve. Answer: 4th arch.
9) Stylopharyngeus nerve supply confirms its origin from?
a) CN V
b) CN VII
c) CN IX
d) CN X
Explanation: The stylopharyngeus muscle is supplied by the glossopharyngeal nerve (CN IX), indicating its third arch origin. Each arch is associated with a specific cranial nerve reflecting its embryologic source. Answer: CN IX (3rd arch).
10) Clinical Case: A surgeon injures the external laryngeal nerve during thyroid surgery. Which arch derivative is affected?
a) 3rd
b) 4th
c) 5th
d) 6th
Explanation: The external laryngeal nerve (branch of superior laryngeal nerve) innervates cricothyroid, derived from the 4th arch. Injury causes monotonous voice due to inability to tense vocal cords. Answer: 4th arch.
Chapter: Anatomy; Topic: Osteology; Subtopic: Secondary Ossification Centers of Long Bones
Keyword Definitions:
Ossification center: Area where bone formation begins during development.
Primary ossification center: Appears first, usually in the diaphysis (shaft) of long bones.
Secondary ossification center: Appears later, usually at the epiphysis (ends) of long bones.
Epiphysis: The rounded ends of a long bone where growth occurs.
Femur: The longest and strongest bone of the human body, forming the thigh.
Lead Question – 2014
Secondary ossification center for lower end of femur?
a) Present at birth
b) Appears at 6 months of age
c) Appears at 1 year of age
d) Appears at 5 years of age
Explanation:
The lower end of femur shows a secondary ossification center that is present at birth. It is one of the earliest secondary centers to appear and serves as a useful indicator for assessing fetal viability in late pregnancy. Its early appearance helps in estimating gestational age radiologically. Answer: Present at birth.
1) The secondary ossification center for the head of femur appears at:
a) Birth
b) 1 year
c) 5 years
d) Puberty
Explanation: The secondary ossification center for the head of femur appears at about 1 year of age and fuses by 18–20 years. It contributes to the growth of the proximal end of the femur and helps maintain the hip joint’s structural integrity. Answer: 1 year.
2) The secondary ossification center for upper end of tibia appears at:
a) Birth
b) 1 year
c) 3 years
d) 5 years
Explanation: The upper end of the tibia develops a secondary ossification center around birth. This site contributes to longitudinal bone growth and is radiologically visible early in life, aiding in age estimation. Answer: Birth.
3) Clinical Case: A newborn X-ray shows an ossification center at distal femur. What does it indicate?
a) Prematurity
b) Full-term baby
c) Skeletal dysplasia
d) Growth delay
Explanation: The presence of a distal femoral ossification center indicates a full-term baby (around 36–38 weeks gestation). Its absence in preterm infants helps assess maturity in forensic and neonatal evaluation. Answer: Full-term baby.
4) Which long bone shows a secondary ossification center appearing before birth?
a) Femur (lower end)
b) Humerus (head)
c) Radius (lower end)
d) Tibia (upper end)
Explanation: The lower end of femur and upper end of tibia are exceptions where secondary ossification centers appear before birth, unlike most long bones. They are used to determine fetal maturity radiologically. Answer: Femur (lower end).
5) Clinical Case: A 10-year-old child fractures the lower end of femur. Which part of bone growth may be affected?
a) Primary ossification center
b) Secondary ossification center
c) Diaphyseal growth plate
d) Epiphyseal cartilage
Explanation: In such fractures, the epiphyseal cartilage (growth plate) near the secondary ossification center may be damaged. This can impair longitudinal growth and cause limb length discrepancy if not properly aligned. Answer: Epiphyseal cartilage.
6) The secondary ossification center for upper end of humerus appears at:
a) Birth
b) 6 months
c) 1 year
d) 3 years
Explanation: The upper end of humerus develops its secondary ossification center at birth. It has two centers — one for the head and another for the greater tubercle, which later fuse. Answer: Birth.
7) Clinical Case: In a neonate, absence of distal femoral ossification center indicates:
a) Full-term gestation
b) Premature birth
c) Congenital femoral hypoplasia
d) Nutritional deficiency
Explanation: Absence of the distal femoral ossification center in a neonate indicates premature birth. It usually appears at around 36 weeks of intrauterine life and serves as a radiologic sign of maturity. Answer: Premature birth.
8) The last secondary ossification center to fuse in the femur is at:
a) Lower end
b) Upper end
c) Head
d) Greater trochanter
Explanation: The head of the femur is the last to fuse, typically by 18–20 years of age. This timing helps in assessing skeletal maturity during forensic and orthopedic evaluation. Answer: Head.
9) Clinical Case: A radiograph shows early fusion of epiphyseal plates at both ends of femur. This may result from:
a) Hypothyroidism
b) Hyperthyroidism
c) Hypogonadism
d) Precocious puberty
Explanation: Early fusion of growth plates occurs in precocious puberty due to premature exposure to sex hormones. This causes stunted growth as bone elongation stops early. Answer: Precocious puberty.
10) Secondary ossification center for greater trochanter appears at:
a) Birth
b) 4 years
c) 10 years
d) 15 years
Explanation: The greater trochanter of the femur develops its secondary ossification center at about 4 years of age. This center fuses later in adolescence. Its appearance pattern helps identify bone age in radiographic studies. Answer: 4 years.
Chapter: Anatomy; Topic: Joints of Thorax; Subtopic: Sternochondral Joints
Keyword Definitions:
Joint: The site where two bones meet, allowing movement or providing stability.
Cartilaginous joint: Bones united by cartilage, allowing limited movement.
Primary cartilaginous joint (synchondrosis): Joined by hyaline cartilage, usually immovable.
Secondary cartilaginous joint (symphysis): Has fibrocartilage, allows limited movement.
Synovial joint: Freely movable joint surrounded by a capsule filled with synovial fluid.
Sternochondral joint: Articulation between the sternum and costal cartilages.
Lead Question – 2014
Sternochondral joint is?
a) Primary cartilaginous
b) Secondary cartilaginous
c) Fibrous
d) Synovial
Explanation:
The sternochondral joints are between the costal cartilages and sternum. The first sternochondral joint is a primary cartilaginous (synchondrosis) joint, while the 2nd to 7th are synovial joints allowing slight gliding movement during respiration. This mixed type of articulation ensures stability with flexibility in thoracic expansion. Answer: Synovial (except 1st – primary cartilaginous).
1) The first sternochondral joint differs from the others because it is:
a) Synovial
b) Primary cartilaginous
c) Secondary cartilaginous
d) Fibrous
Explanation: The first sternochondral joint is a primary cartilaginous (synchondrosis) joint composed of hyaline cartilage, allowing no movement. It provides firm attachment of the first rib to the sternum for stability during respiration. Answer: Primary cartilaginous.
2) The 2nd to 7th sternochondral joints are:
a) Primary cartilaginous
b) Secondary cartilaginous
c) Synovial plane joints
d) Fibrous joints
Explanation: The 2nd–7th sternochondral joints are synovial plane type joints that allow gliding movements. These joints assist in the expansion and contraction of the thoracic cage during breathing. Answer: Synovial plane joints.
3) Clinical Case: A patient with ankylosis of sternochondral joints will have difficulty in:
a) Neck movement
b) Breathing
c) Arm movement
d) Swallowing
Explanation: Ankylosis (fusion) of sternochondral joints restricts thoracic cage expansion, reducing respiratory efficiency. The patient experiences breathing difficulty due to limited rib movement during inspiration. Answer: Breathing.
4) Which joint type unites manubrium and body of sternum?
a) Primary cartilaginous
b) Secondary cartilaginous
c) Synovial
d) Fibrous
Explanation: The manubriosternal joint is a secondary cartilaginous (symphysis) joint composed of fibrocartilage. It provides slight movement during respiration and marks the sternal angle (of Louis). Answer: Secondary cartilaginous.
5) Clinical Case: Pain and tenderness over sternochondral joints may be due to:
a) Costochondritis
b) Osteoporosis
c) Rib fracture
d) Pleural effusion
Explanation: Costochondritis is inflammation of the sternochondral junctions, causing localized anterior chest wall pain. It is benign and self-limiting, often mimicking cardiac chest pain. Answer: Costochondritis.
6) Which rib’s costal cartilage articulates with the manubriosternal joint?
a) 1st rib
b) 2nd rib
c) 3rd rib
d) 4th rib
Explanation: The 2nd costal cartilage articulates at the manubriosternal joint (sternal angle). This landmark is clinically important for rib counting and correlates with the level of the aortic arch and T4 vertebra. Answer: 2nd rib.
7) Clinical Case: A 55-year-old man presents with chest pain localized to the costosternal junction, worse on movement. Most likely cause?
a) Angina pectoris
b) Costochondritis
c) Rib fracture
d) Pleural effusion
Explanation: Localized tenderness and pain on movement without cardiac symptoms indicate costochondritis, an inflammation of the costosternal or sternochondral junctions. Answer: Costochondritis.
8) Which joint helps in the expansion of the chest during inspiration?
a) Costovertebral joint
b) Sternochondral joint
c) Manubriosternal joint
d) Xiphisternal joint
Explanation: The sternochondral joints, especially from 2nd to 7th ribs, allow gliding movements that facilitate chest expansion during inspiration. Answer: Sternochondral joint.
9) The xiphisternal joint becomes ossified at what age?
a) 20 years
b) 30 years
c) 40 years
d) After 40 years
Explanation: The xiphisternal joint, a primary cartilaginous type, ossifies completely by around 40 years. It marks the lower end of the sternal body and the level of T9 vertebra. Answer: After 40 years.
10) Clinical Case: Post-thoracotomy patient has limited chest expansion due to stiff joints at costosternal junction. Type of joint affected?
a) Synovial plane
b) Primary cartilaginous
c) Secondary cartilaginous
d) Fibrous
Explanation: The 2nd–7th sternochondral joints are synovial plane joints. Fibrosis or inflammation in these joints limits thoracic expansion and impairs ventilation. Answer: Synovial plane.
Chapter: Anatomy; Topic: Joints; Subtopic: Innervation of Joints
Keyword Definitions:
Synovium: Thin membrane lining the joint capsule producing synovial fluid.
Capsule: Fibrous tissue enclosing the joint for stability and protection.
Articular cartilage: Smooth avascular tissue covering bone ends to reduce friction.
Ligaments: Connective tissues joining bones to stabilize the joint.
Joint innervation: Supply of nerves to joint structures transmitting pain and proprioception.
Lead Question - 2014
Innervated structures of joints are all except ?
a) Synovium
b) Capsule
c) Articular cartilage
d) Ligaments
Explanation: Articular cartilage is avascular and non-innervated, meaning it lacks both blood vessels and nerve endings. In contrast, the capsule, synovium, and ligaments have rich nerve supplies that convey pain and proprioceptive signals. Therefore, the correct answer is Articular cartilage, which relies on diffusion for nutrition and repair due to absence of nerves and vessels.
1) Pain sensation from the hip joint is carried mainly by:
a) Obturator nerve
b) Sciatic nerve
c) Femoral nerve
d) All of the above
Explanation: The hip joint receives sensory innervation from multiple nerves, including the obturator, femoral, and sciatic nerves. These nerves transmit pain and proprioceptive sensations. Hence, the correct answer is All of the above. Such extensive innervation ensures effective joint protection and reflexive muscular stabilization during movement or injury.
2) Which structure provides proprioceptive feedback from a joint?
a) Articular cartilage
b) Synovium
c) Capsule and ligaments
d) Synovial fluid
Explanation: Proprioception from joints originates mainly from mechanoreceptors present in the joint capsule and ligaments. These receptors sense stretch, position, and movement. Articular cartilage lacks such receptors. Thus, the correct answer is Capsule and ligaments. This feedback system is crucial for coordinated movement and joint stability during locomotion or external stress.
3) Referred pain from the shoulder joint may be felt in:
a) Arm
b) Neck
c) Scapular region
d) All of the above
Explanation: Shoulder joint pain is often referred to the neck, arm, and scapular region due to overlapping nerve supply through the C5–C6 spinal segments. Hence, the correct answer is All of the above. Referred pain reflects the convergence of sensory fibers in the spinal cord from multiple anatomical regions sharing a common root level.
4) Which joint structure has no sensory nerve endings?
a) Ligaments
b) Articular cartilage
c) Capsule
d) Synovium
Explanation: The articular cartilage has no sensory nerve endings, making it insensitive to pain. Damage to cartilage thus presents late clinically. Other structures like ligaments and capsule are richly innervated. Therefore, the correct answer is Articular cartilage. This lack of innervation contributes to painless degeneration in conditions like osteoarthritis until secondary involvement occurs.
5) Which nerve supplies the posterior capsule of the knee joint?
a) Femoral nerve
b) Tibial nerve
c) Common peroneal nerve
d) Saphenous nerve
Explanation: The posterior capsule of the knee joint is supplied by the tibial nerve, which carries sensory and proprioceptive fibers. The femoral and saphenous nerves supply anterior and medial regions respectively. Hence, the correct answer is Tibial nerve. This pattern helps localize knee joint pathology based on pain distribution during clinical examination.
6) A 40-year-old man with knee trauma feels deep joint pain without swelling. Which structure is most likely injured?
a) Capsule
b) Articular cartilage
c) Synovium
d) Ligament
Explanation: Deep pain without inflammation suggests damage to the capsule or ligaments rather than synovium. However, since the capsule carries dense pain receptors, the correct answer is Capsule. Articular cartilage injury usually causes mechanical symptoms. Capsule injury leads to dull, aching pain due to stretch or microtears of the fibrous tissue.
7) During arthroscopy, synovial inflammation causes severe pain due to:
a) Rich vascularity and nerve endings
b) Lack of blood vessels
c) Presence of cartilage
d) Presence of fat pads
Explanation: Synovium is highly vascular and innervated, making inflammation extremely painful. The correct answer is Rich vascularity and nerve endings. This explains why synovitis in rheumatoid arthritis leads to intense pain and tenderness. The vascular network facilitates immune cell infiltration and swelling, worsening the pain during joint motion or pressure.
8) Referred pain from hip joint disease is felt over:
a) Knee
b) Ankle
c) Groin
d) Both a and c
Explanation: Hip joint pain is often referred to the knee and groin through the obturator and femoral nerves (L2–L4). Hence, the correct answer is Both a and c. This overlap occurs because these nerves share spinal roots supplying both joints. Therefore, knee pain may occasionally represent underlying hip pathology rather than local knee disease.
9) Which joint structure is responsible for pain in osteoarthritis?
a) Articular cartilage
b) Subchondral bone and capsule
c) Synovial fluid
d) Meniscus
Explanation: Pain in osteoarthritis arises from the subchondral bone, synovium, and capsule — all innervated tissues. The correct answer is Subchondral bone and capsule. Cartilage degeneration exposes nerve-rich bone leading to deep aching pain. Synovial inflammation adds to the discomfort, making these structures major pain contributors in degenerative joint disease.
10) A patient with rheumatoid arthritis experiences joint tenderness mainly due to:
a) Articular cartilage erosion
b) Synovial inflammation
c) Meniscal tear
d) Ligament laxity
Explanation: Tenderness in rheumatoid arthritis is due to inflammation of the synovium which is richly supplied with pain fibers. Hence, the correct answer is Synovial inflammation. Synovial proliferation (pannus) invades cartilage and bone, but pain originates from the vascular, innervated synovium — the primary site of autoimmune inflammation in rheumatoid arthritis.
Chapter: Anatomy; Topic: Gastrointestinal System; Subtopic: Enteric Nervous System
Keyword Definitions:
Submucosal plexus: Also called Meissner’s plexus, located in the submucosa and regulates glandular secretion and blood flow.
Myenteric plexus: Also known as Auerbach’s plexus, lies between muscle layers and controls peristalsis.
Peristalsis: Coordinated contraction and relaxation of intestinal muscles that move food along the digestive tract.
Enteric nervous system: Intrinsic neural network of the gut functioning independently of the central nervous system.
Parasympathetic innervation: Enhances GI secretion and motility through vagal and sacral outflow.
Lead Question - 2014
Submucosal plexus is ?
a) Myenteric plexus
b) Auerbach's plexus
c) Meissner's plexus
d) Tympanic plexus
Explanation: The submucosal plexus, also known as Meissner’s plexus, lies in the submucosa of the gastrointestinal tract. It primarily controls glandular secretions and local blood flow of the mucosa. In contrast, Auerbach’s (myenteric) plexus regulates smooth muscle activity and peristalsis. Together they form the enteric nervous system, functioning semi-autonomously in digestion.
1) Myenteric plexus is located between:
a) Mucosa and submucosa
b) Circular and longitudinal muscle layers
c) Serosa and muscularis externa
d) Submucosa and serosa
Explanation: The myenteric (Auerbach’s) plexus lies between the circular and longitudinal muscle layers of the gut wall. It coordinates peristaltic activity, controlling rhythmic contractions of smooth muscles. Hence, the correct answer is Circular and longitudinal muscle layers. This plexus is essential for propulsive motility of the gastrointestinal tract and smooth coordination of digestive movements.
2) Meissner’s plexus controls mainly:
a) GI motility
b) Glandular secretion and local blood flow
c) Gastric emptying
d) Defecation reflex
Explanation: Meissner’s plexus, located in the submucosa, regulates glandular secretion and local mucosal blood flow. It doesn’t directly control motility, which is governed by the myenteric plexus. Hence, the correct answer is Glandular secretion and local blood flow. It ensures proper lubrication and enzymatic activity during digestion by modulating secretion rates and mucosal perfusion.
3) In Hirschsprung’s disease, which plexus is absent?
a) Myenteric plexus
b) Submucosal plexus
c) Both Auerbach’s and Meissner’s plexus
d) None of the above
Explanation: Hirschsprung’s disease (congenital aganglionic megacolon) results from the absence of both Auerbach’s and Meissner’s plexuses in affected bowel segments. This leads to a lack of peristalsis, causing functional obstruction and dilation of the proximal colon. Neural crest migration failure during embryogenesis underlies this pathology, leading to chronic constipation and abdominal distension.
4) Which of the following is part of the enteric nervous system?
a) Myenteric plexus
b) Submucosal plexus
c) Both a and b
d) None of the above
Explanation: The enteric nervous system consists of two interconnected plexuses: the myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses. Together, they regulate motility, secretion, and blood flow of the gastrointestinal tract. Hence, the correct answer is Both a and b. They function semi-independently under modulation by parasympathetic and sympathetic inputs, often termed the “second brain” of the gut.
5) Which neurotransmitter is mainly involved in GI peristalsis?
a) Dopamine
b) Acetylcholine
c) Serotonin
d) GABA
Explanation: Acetylcholine is the principal neurotransmitter promoting gastrointestinal smooth muscle contraction and peristalsis. It enhances coordinated contractions mediated by the myenteric plexus. In contrast, sympathetic stimulation inhibits motility. Acetylcholine’s excitatory role ensures proper mixing and propulsion of food, a vital function controlled by enteric and vagal nerve coordination in digestion.
6) A patient with bowel obstruction shows loss of peristalsis. Which plexus is most affected?
a) Meissner’s plexus
b) Myenteric plexus
c) Both
d) None
Explanation: The myenteric (Auerbach’s) plexus is primarily responsible for peristalsis. Damage to this plexus impairs smooth muscle coordination, resulting in paralysis of gut motility. Meissner’s plexus affects secretion rather than movement. Hence, the correct answer is Myenteric plexus. Restoration of peristalsis depends on the integrity of enteric neuronal circuits and their cholinergic transmission efficiency.
7) Which of the following is true about Meissner’s plexus?
a) Lies between two muscle layers
b) Controls secretion and mucosal blood flow
c) Responsible for rhythmic peristalsis
d) Absent in colon
Explanation: Meissner’s plexus lies in the submucosa, not between muscle layers. It regulates mucosal gland secretion and local blood flow. Hence, the correct answer is Controls secretion and mucosal blood flow. It is present throughout the intestine and functions in coordination with the myenteric plexus to ensure optimal digestive enzyme release and mucosal lubrication.
8) A 3-year-old child presents with chronic constipation and distended abdomen. Which of the following is defective?
a) Meissner’s plexus
b) Auerbach’s plexus
c) Both Meissner’s and Auerbach’s plexuses
d) Muscular layer only
Explanation: In congenital aganglionic megacolon (Hirschsprung’s disease), both Meissner’s and Auerbach’s plexuses are absent. Hence, the correct answer is Both Meissner’s and Auerbach’s plexuses. Lack of ganglion cells leads to tonic contraction and functional obstruction. Surgical resection of the aganglionic segment restores normal bowel function in such cases.
9) Which region of the GI tract has the most prominent Meissner’s plexus?
a) Esophagus
b) Stomach
c) Small intestine
d) Rectum
Explanation: The small intestine has a well-developed Meissner’s plexus because of its high secretory and absorptive functions. It regulates secretions from Brunner’s glands and intestinal crypts, facilitating digestion. In contrast, the esophagus has minimal submucosal plexus development. Thus, Meissner’s plexus activity parallels the metabolic demand of mucosal secretion.
10) Injury to the enteric nervous system may lead to:
a) Hypersecretion of gastric acid
b) Loss of coordinated peristalsis
c) Increased intestinal absorption
d) Enhanced mucosal immunity
Explanation: Damage to the enteric nervous system, including Auerbach’s and Meissner’s plexuses, impairs neural regulation of motility and secretion. The most significant effect is loss of coordinated peristalsis. This results in intestinal stasis, distension, and malabsorption. Restoration requires functional neuronal circuits and intact parasympathetic regulation for normal gastrointestinal propulsion.