Subtopic: Interatrial Septum Formation
Keywords & Definitions:
Fossa ovalis: Oval depression in the right atrium, remnant of fetal foramen ovale.
Septum primum: First interatrial septum growing downward during fetal heart development.
Septum secundum: Second crescent-shaped septum overlapping septum primum, forming the foramen ovale.
Ductus arteriosus: Vessel connecting pulmonary artery to aorta in fetus, bypassing lungs.
Ductus venosus: Vessel shunting blood from umbilical vein to inferior vena cava in fetus.
Foramen ovale: Opening in fetal heart allowing blood flow between atria, closes after birth.
Remnant: Vestigial structure from fetal life.
Interatrial septum: Wall between left and right atria.
Embryology: Study of prenatal development.
Patent foramen ovale (PFO): Incomplete closure of foramen ovale after birth.
Lead Question - 2012:
Fossa ovalis is a remnant of?
a) Septum primum
b) Septum secundum
c) Ductus arteriosus
d) Ductus venosus
Explanation & Answer:
The correct answer is a) Septum primum. The fossa ovalis represents the closed remnant of the foramen ovale, which is originally formed by the septum primum during fetal development. After birth, increased left atrial pressure causes fusion of septum primum and septum secundum, closing the foramen ovale and leaving the fossa ovalis.
Q2. What is the function of foramen ovale in fetal circulation?
a) Connects left and right ventricles
b) Allows blood to bypass lungs by flowing between atria
c) Connects pulmonary artery and aorta
d) Connects umbilical vein to inferior vena cava
Explanation & Answer:
Foramen ovale allows oxygenated blood to bypass the non-functioning fetal lungs by flowing directly from right atrium to left atrium, essential for fetal circulation.
Q3. Which structure closes shortly after birth due to increased left atrial pressure?
a) Foramen ovale
b) Ductus arteriosus
c) Ductus venosus
d) Umbilical vein
Explanation & Answer:
The foramen ovale closes functionally shortly after birth as increased pulmonary blood flow raises left atrial pressure, pressing septum primum against septum secundum.
Q4 (Clinical). Patent foramen ovale (PFO) may cause which clinical condition?
a) Stroke due to paradoxical embolism
b) Pulmonary hypertension
c) Aortic stenosis
d) Coarctation of aorta
Explanation & Answer:
PFO can allow venous emboli to bypass lungs and enter systemic circulation causing paradoxical embolism and ischemic stroke, especially after activities increasing right atrial pressure.
Q5. Which fetal vessel connects pulmonary artery to descending aorta?
a) Ductus arteriosus
b) Ductus venosus
c) Foramen ovale
d) Umbilical artery
Explanation & Answer:
The ductus arteriosus shunts blood from pulmonary artery to aorta, bypassing fetal lungs. It normally closes after birth to become ligamentum arteriosum.
Q6. The septum secundum forms which part of the interatrial septum?
a) Thin membranous part
b) Thick muscular ridge
c) Valve of foramen ovale
d) None of the above
Explanation & Answer:
The septum secundum is a thick muscular ridge that overlaps the foramen ovale and works with septum primum to prevent backflow after birth.
Q7. Ductus venosus connects which vessels in fetal circulation?
a) Umbilical vein to inferior vena cava
b) Pulmonary artery to aorta
c) Right atrium to left atrium
d) Umbilical artery to placenta
Explanation & Answer:
Ductus venosus bypasses the liver by connecting umbilical vein directly to the inferior vena cava, facilitating rapid oxygenated blood flow to the heart.
Q8 (Clinical). Which congenital defect results from failure of fusion of septum primum and secundum?
a) Atrial septal defect (ostium secundum type)
b) Ventricular septal defect
c) Patent ductus arteriosus
d) Tetralogy of Fallot
Explanation & Answer:
Failure of septum primum and secundum fusion causes atrial septal defect of ostium secundum type, leading to left-to-right shunt and possible right heart overload.
Q9. Which adult structure corresponds to the ductus arteriosus?
a) Ligamentum arteriosum
b) Ligamentum venosum
c) Fossa ovalis
d) Median umbilical ligament
Explanation & Answer:
After birth, the ductus arteriosus closes and becomes ligamentum arteriosum, a fibrous remnant connecting pulmonary artery and aorta.
Q10. Which statement about fetal circulation is TRUE?
a) Foramen ovale allows blood flow from left atrium to right atrium
b) Ductus arteriosus carries blood from aorta to pulmonary artery
c) Ductus venosus bypasses fetal liver
d) Umbilical arteries carry oxygenated blood
Explanation & Answer:
The ductus venosus connects the umbilical vein to inferior vena cava, allowing oxygen-rich blood to bypass the liver and enter systemic circulation rapidly.
Keywords & Definitions
Pharyngeal arches: Transient embryonic structures forming head–neck skeleton, muscles, arteries, and nerves.
Aortic arch arteries: Arterial segments within each pharyngeal arch that remodel into definitive great vessels.
1st arch artery (Mandibular): Largely regresses; persistent part forms maxillary artery.
2nd arch artery (Hyoid/Stapedial): Forms stapedial and hyoid arteries; mostly regresses postnatally.
3rd arch artery: Forms common carotids and proximal internal carotids.
4th arch artery: Left contributes to aortic arch; right to proximal right subclavian.
6th arch artery: Forms proximal pulmonary arteries; left forms ductus arteriosus.
Stapedial artery: Embryonic vessel through stapes; persistence may cause pulsatile tinnitus/bleeding in ear surgery.
Maxillary artery: Terminal branch of external carotid; derivative of 1st arch artery.
Ductus arteriosus: Left 6th arch derivative connecting pulmonary trunk to aorta in fetus.
Aberrant right subclavian: Vessel coursing behind esophagus due to right 4th arch regression.
Common carotid artery: Major neck artery from 3rd arch; external carotid sprouts from ventral aorta.
Recurrent laryngeal nerve: Loops under 6th arch derivatives; left under ductus/arch, right under subclavian.
Reichert’s cartilage: Cartilage of 2nd arch (stapes, styloid process, lesser hyoid horn).
Meckel’s cartilage: 1st arch cartilage (malleus, incus, sphenomandibular ligament).
Chapter: Embryology – Cardiovascular Development
Topic: Pharyngeal (Branchial) Arch Arteries
Subtopic: Derivatives of Individual Arch Arteries & Clinical Correlates
Lead Question – 2012
Artery of 2nd pharyngeal arch is ?
a) Maxillary artery
b) Stapedial artery
c) Subclavian artery
d) Common carotid artery
Explanation (Answer inside):
The 2nd pharyngeal arch gives rise to the stapedial (and hyoid) arteries, which largely regress postnatally. The maxillary artery is from the 1st arch; the common carotid from the 3rd arch; the subclavian (proximal right) from the 4th arch. Hence, the correct option is b) Stapedial artery.
1) The definitive derivative of the 1st pharyngeal arch artery is:
a) Superior thyroid artery
b) Maxillary artery
c) Stapedial artery
d) Lingual artery
Explanation: The 1st arch artery largely disappears; its remnant persists as the maxillary artery, a major branch of the external carotid. Superior thyroid and lingual arteries arise from the external carotid but are not arch derivatives. Stapedial belongs to the 2nd arch. Correct option: b) Maxillary artery.
2) The 3rd pharyngeal arch artery predominantly forms:
a) External carotid artery entirely
b) Common carotid and proximal internal carotid arteries
c) Vertebral arteries
d) Distal internal carotid artery
Explanation: Third arch arteries become the common carotids and the proximal internal carotids. The external carotid sprouts from the ventral aorta; distal internal carotid derives from dorsal aorta. Vertebral arteries form from intersegmental arteries. Correct option: b) Common carotid and proximal internal carotid arteries.
3) The right 4th pharyngeal arch artery contributes to the:
a) Entire right subclavian artery
b) Proximal segment of right subclavian artery
c) Distal right subclavian via dorsal aorta only
d) Brachiocephalic trunk entirely
Explanation: The right 4th arch forms the proximal right subclavian artery. The distal subclavian arises from the right dorsal aorta and right 7th intersegmental artery. The brachiocephalic trunk develops from the aortic sac. Correct: b) Proximal segment of right subclavian artery.
4) The left 4th pharyngeal arch artery becomes part of the:
a) Left common carotid artery
b) Left pulmonary artery
c) Arch of aorta between left common carotid and left subclavian
d) Descending thoracic aorta
Explanation: The left 4th arch contributes to the arch of aorta segment between left common carotid and left subclavian origins. Left pulmonary is from 6th arch; descending thoracic aorta is dorsal aorta. Correct: c) Arch of aorta between left common carotid and left subclavian.
5) The 6th pharyngeal arch arteries form which key fetal structure?
a) Ductus venosus
b) Ductus arteriosus
c) Ligamentum teres
d) Coronary arteries
Explanation: The sixth (pulmonary) arches produce the proximal pulmonary arteries. On the left, the distal part persists as the ductus arteriosus, later becoming ligamentum arteriosum. Ductus venosus and ligamentum teres are hepatic fetal channels; coronary arteries arise from aortic sinuses. Correct: b) Ductus arteriosus.
6) A patient with pulsatile tinnitus has a vascular middle-ear mass due to a persistent embryonic artery. The vessel most likely persisting is:
a) Stapedial artery
b) Hyoid artery
c) Inferior tympanic artery
d) Ascending pharyngeal artery
Explanation: Persistence of the stapedial artery (2nd arch derivative) may traverse the middle ear, causing pulsatile tinnitus and bleeding risk during otologic surgery. Hyoid artery accompanies stapedial embryologically but usually regresses. Inferior tympanic/ascending pharyngeal are adult branches. Correct: a) Stapedial artery.
7) Aberrant right subclavian artery (dysphagia lusoria) most commonly results from:
a) Persistence of right 4th arch and right dorsal aorta proximally
b) Regression of right 4th arch with persistence of distal right dorsal aorta
c) Persistence of right 6th arch distal segment
d) Failure of left dorsal aorta to form
Explanation: An aberrant right subclavian arises when the right 4th arch regresses and the distal right dorsal aorta persists, so the vessel originates distal to the left subclavian and passes posterior to the esophagus, causing dysphagia. Correct: b) Regression of right 4th arch with persistence of distal right dorsal aorta.
8) The facial nerve is the cranial nerve of which pharyngeal arch, whose artery is the stapedial?
a) First arch
b) Second arch
c) Third arch
d) Fourth arch
Explanation: The second (hyoid) arch is supplied by the facial nerve (CN VII) and has the stapedial/hyoid arteries. The first arch is trigeminal (CN V), third is glossopharyngeal (CN IX), and fourth–sixth are vagus (CN X) branches. Correct: b) Second arch.
9) Interruption of the aortic arch (type B) is classically due to abnormal development of which arch artery?
a) Third arch
b) Fourth arch
c) Fifth arch
d) Sixth arch
Explanation: Type B interruption typically reflects failure involving the left fourth arch segment that normally contributes to the aortic arch between left carotid and subclavian. Third arch forms carotids; sixth forms pulmonary/ductus; a true fifth arch is controversial/transient. Correct: b) Fourth arch.
10) Patent ductus arteriosus represents persistence of a derivative of which embryonic arch?
a) Left 6th arch
b) Right 6th arch
c) Left 4th arch
d) Right 4th arch
Explanation: The ductus arteriosus is the distal portion of the left sixth arch artery. Postnatally, closure forms the ligamentum arteriosum; failure results in PDA with left-to-right shunt and continuous murmur. Right sixth arch does not form a ductus. Correct: a) Left 6th arch.
11) Which vessel is formed by sprouting from the ventral aorta near the third arch rather than directly from an arch artery?
a) External carotid artery
b) Internal carotid artery (proximal)
c) Vertebral artery
d) Subclavian artery (proximal right)
Explanation: The external carotid artery develops as a sprout from the ventral aorta near the third arch, while the proximal internal carotid derives from the third arch itself. Vertebral arteries form from cervical intersegmentals; proximal right subclavian is from the right 4th arch. Correct: a) External carotid artery.
Topic: Male Reproductive Anatomy
Subtopic: Wolffian Duct Derivatives
Keywords & Definitions:
Wolffian duct: Also called mesonephric duct; embryonic structure that develops into male reproductive tract components.
Appendix of testis: Remnant of Mullerian duct found near testis.
Uterus: Female reproductive organ, develops from Mullerian ducts.
Appendix of epididymis: A small stalked appendage on the head of epididymis derived from Wolffian duct.
Hydatid of Morgagni: Small cystic remnant, usually the appendix testis or appendix epididymis.
Mullerian duct: Embryonic duct that forms female reproductive tract structures.
Mesonephric duct: Another name for Wolffian duct, crucial in male reproductive development.
Embryology: The study of development of an organism from fertilization to birth.
Sex differentiation: Process by which the embryo develops into male or female reproductive anatomy.
Remnants: Vestigial structures persisting after development.
Q1 (2012). Which is derived from Wolffian duct?
a) Appendix of testis
b) Uterus
c) Appendix of epididymis
d) Hydatid of margagni
Explanation & Answer:
The correct answer is c) Appendix of epididymis.
The appendix of epididymis is a remnant of the Wolffian (mesonephric) duct, which develops into male reproductive structures such as the epididymis, vas deferens, and seminal vesicles. The appendix testis and uterus derive from the Mullerian duct. Hydatid of Morgagni can refer to remnants from either duct but commonly relates to the appendix testis.
Q2. The Mullerian duct develops into which structure?
a) Vas deferens
b) Uterus
c) Epididymis
d) Seminal vesicle
Explanation & Answer:
The Mullerian duct forms the female reproductive tract, including the uterus, fallopian tubes, and upper vagina. It regresses in males due to anti-Mullerian hormone.
Q3. Which hormone causes regression of Mullerian ducts in males?
a) Testosterone
b) Anti-Mullerian hormone
c) Luteinizing hormone
d) Follicle-stimulating hormone
Explanation & Answer:
Anti-Mullerian hormone, secreted by Sertoli cells in the testes, induces regression of Mullerian ducts during male embryonic development, allowing male duct structures to form.
Q4 (Clinical). Persistent Mullerian duct syndrome results in:
a) Presence of uterus in males
b) Absence of vas deferens
c) Absence of epididymis
d) Normal male reproductive tract
Explanation & Answer:
Persistent Mullerian duct syndrome occurs due to failure of anti-Mullerian hormone action, causing retention of female structures such as uterus and fallopian tubes in males, often leading to infertility and cryptorchidism.
Q5. Which structure arises from the Wolffian duct?
a) Seminal vesicle
b) Fallopian tube
c) Uterine tube
d) Clitoris
Explanation & Answer:
The seminal vesicle is derived from the Wolffian duct and contributes to seminal fluid production in males. Female reproductive structures like the fallopian and uterine tubes arise from the Mullerian duct.
Q6. The appendix testis is a remnant of:
a) Wolffian duct
b) Mullerian duct
c) Urogenital sinus
d) Genital tubercle
Explanation & Answer:
The appendix testis is a vestigial remnant of the Mullerian duct found near the upper pole of the testis, distinct from the appendix of epididymis which is Wolffian.
Q7. The vas deferens develops from:
a) Wolffian duct
b) Mullerian duct
c) Ureteric bud
d) Cloaca
Explanation & Answer:
The vas deferens is a derivative of the Wolffian duct and serves as the main conduit for sperm transport from epididymis to the ejaculatory duct.
Q8 (Clinical). Hydatid of Morgagni torsion presents with:
a) Acute scrotal pain
b) Asymptomatic swelling
c) Urinary retention
d) Fever
Explanation & Answer:
Torsion of the hydatid of Morgagni, a cystic remnant on the testis or epididymis, causes sudden scrotal pain and swelling, often mimicking testicular torsion.
Q9. Which of the following is NOT a derivative of Wolffian duct?
a) Epididymis
b) Seminal vesicle
c) Uterus
d) Vas deferens
Explanation & Answer:
The uterus arises from the Mullerian duct; all other options are derivatives of the Wolffian duct, involved in the male reproductive tract development.
Q10. What triggers the differentiation of Wolffian ducts in males?
a) Estrogen
b) Testosterone
c) Progesterone
d) Anti-Mullerian hormone
Explanation & Answer:
Testosterone secreted by Leydig cells stimulates the Wolffian ducts to differentiate into male internal genital structures such as epididymis, vas deferens, and seminal vesicles.
Subtopic: Coronary Sinus Development
Keywords & Definitions:
Coronary sinus: A large venous channel collecting blood from coronary veins and draining into the right atrium.
Truncus arteriosus: Embryonic arterial outflow tract that later divides into aorta and pulmonary artery.
Conus: Also called conus arteriosus, part of the embryonic outflow tract of the heart.
Sinus venosus: Embryonic structure receiving systemic venous blood, contributes to parts of atria and venous valves.
Atrioventricular (AV) canal: The embryonic heart canal between atria and ventricles, precursor to AV valves.
Embryonic heart: The developing heart in the fetus, undergoing morphogenesis to form adult heart structures.
Venous system: Network of veins returning deoxygenated blood to the heart.
Right atrium: Chamber of the heart receiving systemic venous blood.
Cardiac morphogenesis: Process of heart development and formation of chambers and vessels.
Endocardial cushions: Tissue masses important for septation and valve formation.
Q1 (2012). Coronary sinus develops from?
a) Truncus arteriosus
b) Conus
c) Sinus venosus
d) AV canal
Explanation & Answer:
The correct answer is c) Sinus venosus.
The coronary sinus arises from the left horn of the sinus venosus during embryonic heart development. It serves as the major venous drainage channel for the heart muscle, emptying into the right atrium. The truncus arteriosus and conus are involved in arterial outflow tract formation, while the AV canal develops into the atrioventricular valves.
Q2. The left horn of the sinus venosus forms which adult structure?
a) Coronary sinus
b) Left atrium
c) Pulmonary vein
d) Right atrium
Explanation & Answer:
The left horn of the sinus venosus develops into the coronary sinus, which collects venous blood from the heart muscle. The right horn contributes mainly to the smooth part of the right atrium.
Q3. The smooth part of the right atrium develops from:
a) Truncus arteriosus
b) Left horn of sinus venosus
c) Right horn of sinus venosus
d) AV canal
Explanation & Answer:
The smooth portion of the right atrium (sinus venarum) is derived from the right horn of the sinus venosus as it becomes incorporated into the atrial wall during development.
Q4 (Clinical). Persistent left superior vena cava draining into the coronary sinus is due to failure of regression of:
a) Left anterior cardinal vein
b) Right anterior cardinal vein
c) Sinus venosus
d) AV canal
Explanation & Answer:
Persistent left superior vena cava results from failure of the left anterior cardinal vein to regress. It typically drains into the coronary sinus, which is derived from the left horn of sinus venosus, potentially causing coronary sinus enlargement.
Q5. The atrioventricular canal contributes to:
a) Formation of AV valves
b) Formation of coronary sinus
c) Formation of pulmonary veins
d) Formation of truncus arteriosus
Explanation & Answer:
The AV canal gives rise to endocardial cushions that participate in forming the atrioventricular septum and valves, but it does not contribute to the coronary sinus.
Q6. The truncus arteriosus gives rise to:
a) Pulmonary artery and aorta
b) Coronary sinus
c) Left atrium
d) Right atrium
Explanation & Answer:
The truncus arteriosus divides into the ascending aorta and pulmonary trunk, forming the arterial outflow tracts of the heart, unrelated to venous structures like the coronary sinus.
Q7 (Clinical). An absent coronary sinus may be due to:
a) Agenesis of left horn of sinus venosus
b) Abnormal AV canal development
c) Truncus arteriosus defect
d) Conus malformation
Explanation & Answer:
Agenesis or maldevelopment of the left horn of sinus venosus can result in absent or hypoplastic coronary sinus, affecting venous drainage from the heart muscle.
Q8. The sinus venosus initially receives blood from all except:
a) Common cardinal veins
b) Umbilical veins
c) Vitelline veins
d) Pulmonary veins
Explanation & Answer:
The sinus venosus receives blood from common cardinal, vitelline, and umbilical veins, but pulmonary veins drain separately into the left atrium.
Q9. The venous valves of the heart develop from:
a) Endocardial cushions
b) Sinus venosus
c) AV canal
d) Truncus arteriosus
Explanation & Answer:
Venous valves such as the valve of the inferior vena cava develop from tissues near the sinus venosus region during cardiac development.
Q10. The conus arteriosus contributes to:
a) Right ventricular outflow tract
b) Coronary sinus
c) Left atrium
d) AV valves
Explanation & Answer:
The conus arteriosus forms the smooth part of the right ventricular outflow tract, directing blood into the pulmonary trunk.
Subtopic: Cytotrophoblast Invasion
Keywords & Definitions:
Cytotrophoblast: Inner layer of trophoblast cells that proliferate and invade maternal tissues during implantation.
Decidua parietalis: The part of the decidua lining the non-placental regions of the uterus.
Decidua basalis: The part of the decidua beneath the implanted embryo, forming maternal part of the placenta.
Decidua capsularis: The decidual layer covering the implanted embryo and enclosing the conceptus.
Trophoblast: The outer cell layer of the blastocyst that participates in implantation and placenta formation.
Implantation: Process where the blastocyst embeds into the uterine lining.
Syncytiotrophoblast: Multinucleated outer layer of trophoblast responsible for invading the endometrium and producing hCG.
Uterine stroma: Connective tissue of the uterus that becomes decidua during pregnancy.
hCG (Human chorionic gonadotropin): Hormone secreted by syncytiotrophoblast sustaining early pregnancy.
Decidual reaction: Transformation of uterine stromal cells in response to implantation.
Q1 (2012). Cytotrophoblasts invades ?
a) Decidua parietalis
b) Decidua basalis
c) Decidua capsularis
d) None
Explanation & Answer:
Correct answer: b) Decidua basalis.
Cytotrophoblast cells proliferate and invade the decidua basalis, the maternal part beneath the implanted embryo. This invasion is critical for anchoring the placenta and remodeling maternal spiral arteries to establish adequate blood flow to the developing fetus.
Q2. The outer multinucleated trophoblast layer responsible for uterine invasion is called:
a) Cytotrophoblast
b) Syncytiotrophoblast
c) Epiblast
d) Hypoblast
Explanation & Answer:
Correct answer: b) Syncytiotrophoblast.
The syncytiotrophoblast is a multinucleated, invasive layer of trophoblast cells that erode maternal tissues during implantation and secrete human chorionic gonadotropin (hCG) to maintain pregnancy.
Q3. Which hormone is secreted by the trophoblast to maintain corpus luteum function?
a) Progesterone
b) Estrogen
c) hCG
d) Prolactin
Explanation & Answer:
Correct answer: c) hCG.
Human chorionic gonadotropin (hCG) is secreted by the syncytiotrophoblast and maintains the corpus luteum, which produces progesterone vital for sustaining the endometrium during early pregnancy.
Q4 (Clinical). Defective cytotrophoblast invasion can lead to:
a) Placenta previa
b) Ectopic pregnancy
c) Preeclampsia
d) Molar pregnancy
Explanation & Answer:
Correct answer: c) Preeclampsia.
Inadequate invasion of cytotrophoblasts into maternal spiral arteries results in poor placental perfusion, leading to preeclampsia characterized by hypertension and proteinuria in pregnancy.
Q5. The decidua capsularis is located:
a) Beneath the implanted embryo
b) Covering the embryo and enclosing the gestational sac
c) Lining the uterine cavity away from implantation site
d) Forming the maternal placenta
Explanation & Answer:
Correct answer: b) Covering the embryo and enclosing the gestational sac.
The decidua capsularis covers the implanted embryo and separates it from the uterine cavity, eventually fusing with decidua parietalis as the embryo grows.
Q6. The decidua parietalis is:
a) The decidua beneath the implanted blastocyst
b) The decidua opposite the implantation site
c) The fetal component of the placenta
d) The site of trophoblast invasion
Explanation & Answer:
Correct answer: b) The decidua opposite the implantation site.
The decidua parietalis lines the remainder of the uterine cavity away from the implantation site and eventually fuses with the decidua capsularis.
Q7 (Clinical). Which of the following cells fuse to form the syncytiotrophoblast?
a) Cytotrophoblasts
b) Epiblast cells
c) Mesodermal cells
d) Endodermal cells
Explanation & Answer:
Correct answer: a) Cytotrophoblasts.
Cytotrophoblasts proliferate and fuse to form the multinucleated syncytiotrophoblast, which invades the uterine lining during implantation.
Q8. Which of the following best describes the function of the cytotrophoblast?
a) Hormone secretion
b) Proliferative and invasive layer
c) Formation of amnion
d) Formation of yolk sac
Explanation & Answer:
Correct answer: b) Proliferative and invasive layer.
The cytotrophoblast acts as the source of cells for the expanding syncytiotrophoblast and is actively involved in invading maternal tissues during early pregnancy.
Q9. Which maternal tissue undergoes decidual reaction in response to implantation?
a) Endometrial stromal cells
b) Myometrium
c) Perimetrium
d) Ovarian stroma
Explanation & Answer:
Correct answer: a) Endometrial stromal cells.
The decidual reaction involves transformation of endometrial stromal cells into large, secretory decidual cells that support embryo implantation and placental formation.
Q10. Human chorionic gonadotropin (hCG) is detected in maternal blood by:
a) 5th day after fertilization
b) 7th-10th day after fertilization
c) 15th day after fertilization
d) 21st day after fertilization
Explanation & Answer:
Correct answer: b) 7th-10th day after fertilization.
hCG secretion by syncytiotrophoblast begins shortly after implantation, around 7-10 days post fertilization, and can be detected in maternal serum and urine to confirm pregnancy.
Subtopic: Development of the Peritoneal Cavity
Keywords & Definitions:
Mesenchyme: Embryonic connective tissue derived mainly from mesoderm, forming connective tissues, blood, and lymphatic structures.
Intraembryonic coelom: The cavity formed within the lateral plate mesoderm during embryonic folding, giving rise to body cavities.
Ectoderm: The outer germ layer forming the nervous system, epidermis, and related structures.
Endoderm: The innermost germ layer forming epithelial linings of the gastrointestinal tract, respiratory tract, and glands.
Peritoneal cavity: The space within the abdomen lined by peritoneum, housing abdominal organs.
Pleural cavity: Thoracic cavity surrounding each lung.
Pericardial cavity: Space enclosing the heart within the pericardium.
Lateral plate mesoderm: Mesoderm layer split into somatic and splanchnic layers, forming body cavities and their linings.
Septum transversum: Mesodermal tissue contributing to diaphragm formation.
Mesentery: Double layer of peritoneum that suspends and supports organs in the abdominal cavity.
Q1 (2012). Development of peritoneal cavity is from?
a) Mesenchyme
b) Intraembryonic coelom
c) Ectoderm
d) Endoderm
Explanation & Answer:
Correct answer: b) Intraembryonic coelom.
The peritoneal cavity originates from the intraembryonic coelom formed within the lateral plate mesoderm during the 3rd week. This cavity later partitions into the peritoneal, pleural, and pericardial cavities. Proper development is crucial, as abnormal folding or partitioning can lead to congenital diaphragmatic hernias.
Q2. The intraembryonic coelom first appears during:
a) 1st week
b) 2nd week
c) 3rd week
d) 4th week
Explanation & Answer:
Correct answer: c) 3rd week.
The intraembryonic coelom develops as spaces appear within the lateral plate mesoderm during the 3rd week of development, eventually fusing to form a horseshoe-shaped cavity that becomes the basis of the major body cavities.
Q3. Which embryonic layer forms the lining epithelium of the peritoneal cavity?
a) Somatic mesoderm
b) Splanchnic mesoderm
c) Ectoderm
d) Endoderm
Explanation & Answer:
Correct answer: a) Somatic mesoderm.
The parietal peritoneum is derived from somatic mesoderm, while visceral peritoneum is derived from splanchnic mesoderm. This explains why parietal peritoneum pain is sharp and well localized, while visceral pain is dull and poorly localized.
Q4 (Clinical). A neonate is diagnosed with omphalocele. The developmental defect primarily involves:
a) Ectodermal folding defect
b) Endodermal failure
c) Intraembryonic coelom partition defect
d) Failure of gut retraction
Explanation & Answer:
Correct answer: d) Failure of gut retraction.
In omphalocele, midgut fails to return to the peritoneal cavity after physiological herniation. The peritoneal cavity’s development and folding are essential to prevent this defect.
Q5. The septum transversum plays a major role in the formation of:
a) Peritoneal cavity
b) Diaphragm
c) Pleura
d) Pericardium
Explanation & Answer:
Correct answer: b) Diaphragm.
The septum transversum forms the central tendon of the diaphragm and partially separates the thoracic and abdominal cavities before complete partitioning by the pleuroperitoneal membranes.
Q6. Which structure separates the peritoneal cavity from the pleural cavities in early development?
a) Septum transversum
b) Pleuroperitoneal membranes
c) Diaphragmatic muscle
d) Mesentery
Explanation & Answer:
Correct answer: b) Pleuroperitoneal membranes.
These membranes grow to close the pericardioperitoneal canals, completing the separation of the pleural and peritoneal cavities.
Q7 (Clinical). A defect in closure of the pleuroperitoneal membrane results in:
a) Hiatal hernia
b) Bochdalek hernia
c) Morgagni hernia
d) Omphalocele
Explanation & Answer:
Correct answer: b) Bochdalek hernia.
Bochdalek hernia is a posterolateral congenital diaphragmatic hernia caused by failure of pleuroperitoneal membrane fusion, allowing abdominal organs into the thoracic cavity.
Q8. The mesentery suspending the midgut from the dorsal body wall is derived from:
a) Somatic mesoderm
b) Splanchnic mesoderm
c) Ectoderm
d) Endoderm
Explanation & Answer:
Correct answer: b) Splanchnic mesoderm.
The dorsal mesentery is from splanchnic mesoderm and provides a pathway for blood vessels, lymphatics, and nerves to the gut.
Q9. Which event marks the final separation of the peritoneal and pericardial cavities?
a) Folding of the embryo
b) Formation of the diaphragm
c) Closure of the neural tube
d) Formation of the gut tube
Explanation & Answer:
Correct answer: b) Formation of the diaphragm.
Completion of the diaphragm closes the communication between the thoracic and abdominal cavities.
Q10. The visceral peritoneum is derived from:
a) Somatic mesoderm
b) Splanchnic mesoderm
c) Endoderm
d) Ectoderm
Explanation & Answer:
Correct answer: b) Splanchnic mesoderm.
The splanchnic mesoderm forms the visceral layer of the peritoneum covering abdominal organs, in contrast to the somatic mesoderm-derived parietal layer.
Q11. The peritoneal cavity communicates with the extraembryonic coelom through:
a) Primitive streak
b) Umbilical ring
c) Neurenteric canal
d) Pharyngeal membrane
Explanation & Answer:
Correct answer: b) Umbilical ring.
Early in development, the intraembryonic coelom is continuous with the extraembryonic coelom at the umbilical ring, allowing passage of yolk sac and connecting stalk structures.
Subtopic: Endodermal Derivatives
Keywords & Definitions:
Endoderm: Innermost germ layer forming epithelial lining of the gastrointestinal tract, respiratory tract, and associated glands.
Gall bladder: A small sac beneath the liver storing and releasing bile, derived from endoderm.
Lens: Transparent biconvex structure of the eye, derived from surface ectoderm.
Spleen: Lymphoid organ derived from mesoderm, involved in immune response and RBC breakdown.
Lymph nodes: Secondary lymphoid organs derived from mesoderm, filtering lymph fluid.
Pharyngeal pouches: Endodermal outpocketings forming glands and ear structures.
Pancreas: Digestive and endocrine gland derived from endoderm.
Thyroid gland: Endocrine gland in the neck, derived from endoderm of the floor of the pharynx.
Respiratory tract: Airway system from nasal cavity to alveoli, derived from foregut endoderm.
Urinary bladder epithelium: Inner lining of the bladder derived from endoderm of the urogenital sinus.
Q1 (2012). Which of the following is derived from endoderm?
a) Gall bladder
b) Lens
c) Spleen
d) Lymph nodes
Explanation & Answer:
Correct answer: a) Gall bladder.
The gall bladder develops from the hepatic diverticulum of the foregut endoderm. Lens is from surface ectoderm, spleen and lymph nodes are mesodermal. Recognizing embryonic origins is crucial for understanding congenital malformations, such as biliary atresia, which arises from faulty endodermal development.
Q2. The epithelial lining of the trachea is derived from:
a) Mesoderm
b) Endoderm
c) Ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm.
The respiratory epithelium originates from the foregut endoderm, while surrounding cartilage and smooth muscle come from splanchnic mesoderm. This distinction explains why certain congenital airway defects have combined epithelial and structural abnormalities.
Q3. The thyroid gland originates from:
a) Endoderm of primitive pharynx
b) Mesoderm
c) Neural crest
d) Ectoderm
Explanation & Answer:
Correct answer: a) Endoderm of primitive pharynx.
The thyroid develops from a median endodermal thickening in the floor of the pharynx. Migration defects can cause ectopic thyroid tissue along the thyroglossal duct pathway.
Q4 (Clinical). A newborn with respiratory distress is found to have tracheoesophageal fistula. Which germ layer defect is implicated?
a) Ectoderm
b) Endoderm
c) Mesoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm.
Both trachea and esophagus arise from the foregut endoderm. Separation failure during development results in a fistula, causing aspiration and feeding difficulties in neonates.
Q5. Which is NOT an endodermal derivative?
a) Liver
b) Pancreas
c) Adrenal medulla
d) Gall bladder
Explanation & Answer:
Correct answer: c) Adrenal medulla.
Adrenal medulla originates from neural crest cells (ectodermal origin), while liver, pancreas, and gall bladder are from foregut endoderm.
Q6. Epithelial lining of the urinary bladder develops from:
a) Mesoderm
b) Endoderm of urogenital sinus
c) Ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm of urogenital sinus.
The inner epithelium of the bladder is from endoderm, while connective tissue and muscle layers are from splanchnic mesoderm.
Q7 (Clinical). A patient with chronic pancreatitis undergoes histological examination. The acinar cells are derived from which germ layer?
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: a) Endoderm.
Both exocrine and endocrine parts of the pancreas originate from endodermal buds of the foregut, explaining the shared embryological basis for pancreatic and biliary anomalies.
Q8. Which part of the ear is endodermal in origin?
a) Tympanic membrane
b) Eustachian tube
c) Pinna
d) External auditory canal
Explanation & Answer:
Correct answer: b) Eustachian tube.
The Eustachian tube and middle ear cavity arise from the first pharyngeal pouch (endoderm), while pinna and external canal are ectodermal.
Q9. The epithelial lining of the anal canal above the pectinate line is derived from:
a) Ectoderm
b) Endoderm
c) Mesoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Endoderm.
Above the pectinate line, the anal canal develops from hindgut endoderm, while below it comes from ectoderm, explaining different lymphatic drainage and nerve supply.
Q10. Which pharyngeal pouch gives rise to the thymus?
a) First
b) Second
c) Third
d) Fourth
Explanation & Answer:
Correct answer: c) Third.
The thymus develops from the ventral part of the third pharyngeal pouch (endoderm), migrating to the anterior mediastinum.
Q11. Which of the following is an endodermal derivative?
a) Parathyroid gland
b) Epidermis
c) Skeletal muscle
d) Cornea
Explanation & Answer:
Correct answer: a) Parathyroid gland.
Parathyroid glands develop from the dorsal portions of the third and fourth pharyngeal pouches (endodermal origin), playing a key role in calcium regulation.
Subtopic: Ectodermal Derivatives
Keywords & Definitions:
Ectoderm: Outer germ layer forming skin, nervous system, and certain sensory organs.
Endoderm: Innermost germ layer forming the lining of the gut, respiratory tract, and glands.
Mesoderm: Middle germ layer forming muscles, bones, circulatory system, and connective tissues.
Lens: Transparent structure of the eye focusing light on the retina.
Eustachian tube: Tube connecting the middle ear to the nasopharynx, equalizing pressure.
Brain: Central organ of the nervous system derived from neural tube.
Retina: Light-sensitive tissue at the back of the eye derived from neural ectoderm.
Neural crest cells: Ectodermal cells contributing to peripheral nerves, melanocytes, and craniofacial structures.
Pharyngeal pouches: Endodermal outpocketings contributing to ear, tonsils, and glands.
Embryonic germ layers: Three primary cell layers in early development—ectoderm, mesoderm, endoderm.
Q1 (2012). All are derived from ectoderm except?
a) Lens
b) Eustachian tube
c) Brain
d) Retina
Explanation & Answer:
Correct answer: b) Eustachian tube.
The Eustachian tube develops from the first pharyngeal pouch, which is endodermal in origin. Lens, brain, and retina are ectodermal derivatives. Lens develops from surface ectoderm, brain and retina from neural ectoderm. Knowing germ layer origins helps in identifying congenital anomalies.
Q2. Which ectodermal structure forms the enamel of teeth?
a) Neural crest
b) Surface ectoderm
c) Endoderm
d) Mesoderm
Explanation & Answer:
Correct answer: b) Surface ectoderm.
Enamel is produced by ameloblasts derived from surface ectoderm. The underlying dentin and pulp originate from mesodermal tissues. This distinction is important in dental pathology and congenital tooth disorders.
Q3. The pituitary gland's anterior lobe develops from:
a) Neuroectoderm
b) Surface ectoderm
c) Endoderm
d) Mesoderm
Explanation & Answer:
Correct answer: b) Surface ectoderm.
The anterior pituitary (adenohypophysis) develops from Rathke’s pouch, an outgrowth of surface ectoderm from the stomodeum. The posterior pituitary (neurohypophysis) arises from neuroectoderm.
Q4 (Clinical). A newborn presents with congenital absence of the pineal gland. Which germ layer was likely affected?
a) Surface ectoderm
b) Neuroectoderm
c) Endoderm
d) Mesoderm
Explanation & Answer:
Correct answer: b) Neuroectoderm.
The pineal gland originates from neuroectoderm of the diencephalon. Damage to this layer during embryogenesis can impair melatonin production and disrupt circadian rhythm.
Q5. Which is NOT a derivative of neural crest cells?
a) Melanocytes
b) Adrenal medulla
c) Schwann cells
d) Retina
Explanation & Answer:
Correct answer: d) Retina.
Retina arises from neural ectoderm, not neural crest. Neural crest cells contribute to melanocytes, adrenal medulla, craniofacial cartilage, and Schwann cells.
Q6. Cornea is derived from:
a) Ectoderm and mesoderm
b) Endoderm
c) Mesoderm only
d) Ectoderm only
Explanation & Answer:
Correct answer: a) Ectoderm and mesoderm.
The corneal epithelium is derived from surface ectoderm, while stroma and endothelium arise from mesodermal mesenchyme.
Q7 (Clinical). A defect in neural tube closure will primarily affect which ectodermal derivatives?
a) Peripheral nerves
b) Brain and spinal cord
c) Adrenal cortex
d) Epidermis
Explanation & Answer:
Correct answer: b) Brain and spinal cord.
Neural tube defects, such as spina bifida or anencephaly, arise from failure of neural ectoderm closure, affecting the central nervous system.
Q8. Which pharyngeal pouch gives rise to the Eustachian tube?
a) First
b) Second
c) Third
d) Fourth
Explanation & Answer:
Correct answer: a) First.
The first pharyngeal pouch develops into the Eustachian tube and middle ear cavity, lined by endoderm.
Q9. Epidermis of skin is derived from:
a) Mesoderm
b) Endoderm
c) Surface ectoderm
d) Neural crest
Explanation & Answer:
Correct answer: c) Surface ectoderm.
Surface ectoderm forms the epidermis, hair, nails, and glands of the skin. The dermis is mostly mesodermal in origin.
Q10. The inner ear’s membranous labyrinth develops from:
a) Endoderm
b) Surface ectoderm
c) Mesoderm
d) Neural crest
Explanation & Answer:
Correct answer: b) Surface ectoderm.
The otic placode, a thickening of surface ectoderm, invaginates to form the membranous labyrinth of the inner ear.
Q11. Which part of the eye is mesodermal in origin?
a) Lens
b) Retina
c) Choroid
d) Corneal epithelium
Explanation & Answer:
Correct answer: c) Choroid.
The choroid, sclera, and part of the cornea are mesodermal derivatives, providing vascular supply and structural support to the eye.
Chapter: Reproductive System
Topic: Male Reproductive Physiology
Subtopic: Sperm Chromosomes
Keyword Definitions:
Sperm: Male gamete responsible for fertilization.
X chromosome: Larger sex chromosome carrying more genes.
Y chromosome: Smaller sex chromosome determining male sex.
Motility: Ability of sperm to swim toward the ovum.
Chromosomal sex determination: Process where X or Y sperm decides offspring’s sex.
Lead Question – 2012
Sperm chromosome faster is -
a) X chromosome
b) Y chromosome
c) Both same
d) None
Explanation: Y chromosome-bearing sperms are lighter and move faster due to their smaller size, whereas X sperms are heavier but live longer. Therefore, Answer: (b) Y chromosome. Clinically, this helps explain sex selection probabilities but natural fertilization remains random. Y sperms reach the ovum quicker but may die sooner.
Question 2. Which chromosome-bearing sperm has a longer lifespan in the female reproductive tract?
a) X chromosome
b) Y chromosome
c) Both same
d) None
Explanation: X chromosome sperms are larger, more resilient, and survive longer (up to 72 hours), while Y sperms die earlier. Thus, Answer: (a) X chromosome. This explains timing-based conception theories clinically, although fertilization chances remain probabilistic.
Question 3. Which type of sperm is more likely to fertilize if intercourse happens 2-3 days before ovulation?
a) X chromosome sperm
b) Y chromosome sperm
c) Both equal
d) None
Explanation: Since X sperms live longer in the cervical mucus, they are more likely to fertilize when intercourse is days before ovulation. Hence, Answer: (a) X chromosome sperm. Clinically linked to natural family planning theories.
Question 4. Which type of sperm is more heat sensitive?
a) X sperm
b) Y sperm
c) Both equal
d) None
Explanation: Y chromosome sperms are more fragile and heat-sensitive, reducing their survival in unfavorable environments. Answer: (b) Y sperm. Clinically important in infertility where scrotal heat affects sperm survival.
Question 5. Which sperm chromosome has higher DNA content?
a) X sperm
b) Y sperm
c) Both equal
d) None
Explanation: X sperms carry larger DNA content as the X chromosome has more genetic material than the smaller Y chromosome. Answer: (a) X sperm. Clinically, this explains slight size differences seen under advanced imaging.
Question 6. Which sperm is more likely to produce a male child?
a) X sperm
b) Y sperm
c) Both equal
d) None
Explanation: Fertilization by Y sperm results in XY (male) offspring, while X sperm results in XX (female). Answer: (b) Y sperm. Clinical relevance in genetic counseling and sex-linked inheritance discussions.
Question 7. Which factor favors fertilization by Y sperms?
a) Acidic cervical mucus
b) Alkaline cervical mucus
c) Neutral pH
d) None
Explanation: Y sperms survive better in alkaline conditions, which favor their motility and fertilizing ability. Answer: (b) Alkaline cervical mucus. Clinical relevance in infertility treatments.
Question 8. Which sperm is slower but survives longer in the female tract?
a) X sperm
b) Y sperm
c) Both equal
d) None
Explanation: X sperms are slower but have greater survival ability, lasting up to 3 days, unlike Y sperms. Answer: (a) X sperm. Useful in understanding natural conception probabilities.
Question 9. Which sperm is more vulnerable to vaginal acidic pH?
a) X sperm
b) Y sperm
c) Both equal
d) None
Explanation: Y sperms are more fragile and less tolerant to acidic environments, making them more vulnerable. Answer: (b) Y sperm. Clinical importance in cases of unexplained infertility due to pH imbalance.
Question 10. In assisted reproduction, which sperm selection may reduce sex-linked disease inheritance in males?
a) X sperm selection
b) Y sperm selection
c) Both equal
d) None
Explanation: Selecting X sperms reduces the chance of sex-linked diseases (e.g., hemophilia, Duchenne muscular dystrophy) since these occur in males (XY). Answer: (a) X sperm selection. Clinical use in IVF with sperm sorting.
Question 11. Which sperm is responsible for sex determination of offspring?
a) X sperm
b) Y sperm
c) Both
d) None
Explanation: Female ovum always carries X chromosome, so the sperm (X or Y) determines the child’s sex. Answer: (c) Both. Clinically used in counseling families with misconceptions about sex determination.
Subtopic: Spermatogenesis and Chromosome Number
Keywords:
Haploid: Cells with a single set of chromosomes (n).Diploid: Cells with two sets of chromosomes (2n).
Spermatogonia: Mitotically active diploid germ cells in testis.
Primary spermatocyte: Diploid cell entering meiosis I (2n).
Secondary spermatocyte: Haploid chromosome number but chromatids duplicated (n).
Spermatid: Haploid cell after meiosis II that differentiates into sperm.
Meiosis I: Reduction division that separates homologous chromosomes.
Meiosis II: Equational division that separates sister chromatids.
Non-disjunction: Failure of chromosome separation causing aneuploidy.
Synapsis: Homologous chromosome pairing during prophase I.
Crossing-over: Exchange of genetic material during synapsis.
Spermiogenesis: Maturation of spermatids into spermatozoa.
Sertoli cells: Support and nourish developing germ cells.
Leydig cells: Produce testosterone in the testes.
Lead Question - 2012
Haploid number of chromosomes is seen in?
a) Spermatogonia
b) Primary spermatocytes
c) Secondary spermatocyte
d) None
Explanation & Answer:
The correct answer is (c) Secondary spermatocyte. Spermatogonia (2n) divide mitotically to form primary spermatocytes (2n). Meiosis I in primary spermatocytes produces secondary spermatocytes, which are haploid (n) in chromosome number but still have duplicated chromatids. Meiosis II then produces spermatids (n, single chromatids). Haploidy first appears in secondary spermatocytes, marking the reductional division.
Q2. Crossing-over during meiosis occurs in:
a) Prophase I
b) Metaphase I
c) Anaphase I
d) Telophase I
Explanation & Answer:
Correct answer: (a) Prophase I. Crossing-over occurs during pachytene stage of prophase I, where homologous chromosomes undergo synapsis and form chiasmata. This allows genetic recombination, increasing diversity in gametes. Defects in this process can cause chromosomal abnormalities, infertility, or miscarriage, and are often studied in reproductive genetics.
Q3. Primary spermatocyte arrest on biopsy will show:
a) Absence of spermatogonia
b) Accumulation of primary spermatocytes
c) Abundance of spermatids
d) Leydig cell hyperplasia only
Explanation & Answer:
Correct answer: (b) Accumulation of primary spermatocytes. Arrest before completion of meiosis I leads to accumulation of these cells and absence of downstream spermatids. Causes include genetic defects in recombination, hormonal imbalance, and toxin exposure. Clinically, this results in reduced sperm count and infertility.
Q4. Which best describes secondary spermatocytes?
a) Diploid cells entering meiosis I
b) Haploid cells with duplicated chromatids
c) Haploid cells with single chromatids
d) Identical to spermatogonia
Explanation & Answer:
Correct answer: (b) Haploid cells with duplicated chromatids. They result from meiosis I and undergo meiosis II to produce spermatids. This distinction is important in cytogenetics when assessing chromosome number and structure during different stages of gametogenesis.
Q5. Chromosome number reduces from diploid to haploid during:
a) Spermatogonial mitosis
b) Meiosis I
c) Meiosis II
d) Spermiogenesis
Explanation & Answer:
Correct answer: (b) Meiosis I. This reductional division separates homologous chromosomes, halving the chromosome number. Errors in meiosis I, such as nondisjunction, can produce aneuploid gametes leading to genetic disorders like Down syndrome or Klinefelter syndrome.
Q6. A 47,XXY karyotype is most often due to:
a) Mitosis in spermatogonia
b) Meiosis I nondisjunction
c) Meiosis II nondisjunction
d) Postzygotic error
Explanation & Answer:
Correct answer: (b) Meiosis I nondisjunction. This results in gametes with an extra sex chromosome, producing Klinefelter syndrome when fertilized with a normal gamete. Both maternal and paternal errors are possible, but paternal meiosis I errors are common in such cases.
Q7. Spermatogonia are:
a) Haploid cells
b) Diploid germ-line stem cells
c) Immature sperm
d) Sertoli cell precursors
Explanation & Answer:
Correct answer: (b) Diploid germ-line stem cells. They divide mitotically to maintain the germ cell pool and produce primary spermatocytes. Loss of spermatogonia due to toxins, chemotherapy, or radiation can cause permanent infertility.
Q8. Many spermatids but few mature sperm suggest a defect in:
a) Spermatogonial mitosis
b) Meiosis I
c) Spermiogenesis
d) Epididymal transit
Explanation & Answer:
Correct answer: (c) Spermiogenesis. This maturation step shapes spermatids into motile spermatozoa. Defects cause teratozoospermia or asthenozoospermia, leading to infertility despite normal chromosome number and meiosis.
Q9. Cells supporting germ cells in seminiferous tubules are:
a) Leydig cells
b) Sertoli cells
c) Spermatids
d) Myoid cells
Explanation & Answer:
Correct answer: (b) Sertoli cells. They form the blood–testis barrier, secrete androgen-binding protein, and nourish developing sperm. Damage to Sertoli cells leads to defective spermatogenesis and infertility.
Q10. Chromosomes with single chromatids first appear in:
a) Primary spermatocytes
b) Secondary spermatocytes
c) Spermatids
d) Spermatogonia
Explanation & Answer:
Correct answer: (c) Spermatids. These are produced after meiosis II, where sister chromatids separate, leaving single-chromatid chromosomes. This is a key distinction from secondary spermatocytes, which still have duplicated chromatids.
Q11. Unbalanced gametes in balanced translocation carriers arise from:
a) Spermatogonial mitosis
b) Abnormal meiosis I segregation
c) Meiosis II cytokinesis failure
d) Spermiogenesis defect
Explanation & Answer:
Correct answer: (b) Abnormal meiosis I segregation. Translocated chromosomes form quadrivalents, and improper segregation produces gametes with duplications or deletions, leading to miscarriage or congenital anomalies despite normal phenotype in the carrier.