Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 261: In the ovarian cycle, increased levels of LH are primarily due to:

A. Increased Progesterone
B. Increased Estrogen (Correct Answer)
C. Increased FSH
D. Increased Androgens

Explanation: **Explanation:** The ovarian cycle is governed by a complex feedback loop between the ovaries and the hypothalamus-pituitary axis. The correct answer is **Increased Estrogen** because of the unique "positive feedback" mechanism that triggers the LH surge. 1. **Why Estrogen is Correct:** Throughout most of the follicular phase, estrogen exerts negative feedback on LH and FSH. However, once the dominant follicle produces sustained, high levels of estrogen (typically >200 pg/mL for ~48 hours), the feedback switch flips from negative to **positive**. This high concentration of estrogen stimulates the anterior pituitary to release a massive burst of Luteinizing Hormone (LH), known as the **LH surge**, which is essential for ovulation. 2. **Why Other Options are Incorrect:** * **Progesterone:** During the follicular phase, progesterone levels are low. High progesterone (seen in the luteal phase) exerts strong **negative feedback** on LH and FSH to prevent a second ovulation. * **FSH:** While FSH rises slightly before the LH surge, it does not cause the LH surge. In fact, LH and FSH are both stimulated by GnRH pulses, which are accelerated by high estrogen. * **Androgens:** Androgens (like androstenedione) are precursors to estrogen. High levels of androgens (as seen in PCOS) actually inhibit normal ovulation rather than triggering the LH surge. **High-Yield Clinical Pearls for NEET-PG:** * **The Trigger:** Ovulation occurs approximately **24–36 hours** after the peak of estrogen and **10–12 hours** after the LH surge. * **Meiosis:** The LH surge is responsible for the completion of **Meiosis I**, arresting the oocyte in Metaphase of Meiosis II. * **Enzymatic Action:** LH stimulates the production of prostaglandins and proteolytic enzymes (collagenase) that rupture the follicular wall.

Question 262: Testosterone is secreted by:

A. Leydig cells (Correct Answer)
B. Sertoli cells
C. Cowper's gland
D. Intermediate cells

Explanation: **Explanation:** **Correct Answer: A. Leydig cells** Leydig cells (also known as interstitial cells of Leydig) are located in the connective tissue between the seminiferous tubules. Their primary function is the synthesis and secretion of **testosterone** in response to **Luteinizing Hormone (LH)** from the anterior pituitary. LH binds to G-protein coupled receptors on Leydig cells, increasing cAMP and activating protein kinase A, which initiates the conversion of cholesterol to testosterone. **Analysis of Incorrect Options:** * **B. Sertoli cells:** Located within the seminiferous tubules, these are "nurse cells." They do not secrete testosterone; instead, they secrete **Androgen Binding Protein (ABP)**, Inhibin B, and Anti-Müllerian Hormone (AMH). They support spermatogenesis under the influence of FSH. * **C. Cowper’s gland:** Also known as bulbourethral glands, these secrete a clear, alkaline pre-ejaculate fluid that lubricates the urethra and neutralizes acidic urine residue. They have no endocrine function. * **D. Intermediate cells:** This is a non-specific term and not a recognized site for androgen synthesis in the male reproductive system. **High-Yield Clinical Pearls for NEET-PG:** * **LH acts on Leydig cells** (Mnemonic: **L**H = **L**eydig). * **FSH acts on Sertoli cells** (Mnemonic: **F**SH = **S**ertoli). * **Blood-Testis Barrier:** Formed by tight junctions between Sertoli cells. * **Rate-limiting step:** The conversion of cholesterol to pregnenolone by the enzyme *cholesterol side-chain cleavage enzyme* (P450scc) is the key regulated step in testosterone production. * **Testosterone levels:** Highest in the early morning due to diurnal variation.

Question 263: The Y chromosome carries a gene on its short arm that codes for what?

A. Testosterone
B. Mullerian Inhibiting Factor (MIF)
C. Testes-determining factor (TDF) (Correct Answer)
D. Progesterone

Explanation: ### Explanation The correct answer is **Testes-determining factor (TDF)**. **1. Why TDF is Correct:** The sex of an individual is determined by the presence or absence of the **SRY gene** (*Sex-determining Region of the Y chromosome*), located on the **short arm (p arm)** of the Y chromosome. This gene codes for a protein called the **Testes-determining factor (TDF)**. TDF acts as a master transcription factor that triggers the undifferentiated primordial gonads to differentiate into **testes**. Once the testes are formed, they begin secreting hormones (Testosterone and MIF) that drive male phenotypic development. **2. Why Other Options are Incorrect:** * **Testosterone (A):** This is a steroid hormone secreted by the **Leydig cells** of the fetal testes, not directly coded by a gene on the Y chromosome. Its production is a *downstream effect* of TDF action. * **Mullerian Inhibiting Factor (B):** Also known as Anti-Mullerian Hormone (AMH), it is a glycoprotein secreted by **Sertoli cells**. While its production is triggered by the development of testes, the gene for MIF is actually located on **Chromosome 19**. * **Progesterone (D):** This is a precursor for other steroid hormones and a primary female reproductive hormone secreted by the corpus luteum and placenta. It is not Y-chromosome dependent. **3. High-Yield Clinical Pearls for NEET-PG:** * **SRY Gene Location:** Short arm of Y chromosome (Yp11.3). * **Developmental Timeline:** Gonadal differentiation occurs around the **6th–7th week** of gestation. * **MIF Function:** Causes regression of Paramesonephric (Mullerian) ducts. * **Testosterone Function:** Stimulates development of Mesonephric (Wolffian) ducts into the internal male genitalia (Epididymis, Vas deferens, Seminal vesicles). * **Dihydrotestosterone (DHT):** Responsible for the development of external male genitalia and the prostate.

Question 264: Which of the following statements regarding the blood-testis barrier is incorrect?

A. It is formed by Sertoli cells.
B. It is formed before primary spermatogenesis. (Correct Answer)
C. Rupture of the barrier can elicit an immune response to germ cells.
D. Germ cells are not necessary for the formation of the barrier.

Explanation: ### Explanation **1. Why Option B is the Correct (Incorrect Statement):** The blood-testis barrier (BTB) is **not** formed before primary spermatogenesis. In humans, the BTB develops during **puberty**, coinciding with the onset of spermatogenesis and the rise in gonadotropins. Before puberty, the seminiferous tubules are solid cords without a functional barrier. The barrier is essential to protect the developing haploid germ cells (which appear only after puberty) from the immune system. **2. Analysis of Other Options:** * **Option A (Correct Statement):** The BTB is formed by specialized **tight junctions (Zonula occludens)** between the basolateral membranes of adjacent **Sertoli cells**. These junctions divide the seminiferous epithelium into a basal compartment and an adluminal compartment. * **Option C (Correct Statement):** Since spermatogenesis begins at puberty, the immune system (which develops self-tolerance in infancy) recognizes haploid sperm cells as "foreign" (antigenic). Rupture of the BTB (due to trauma, infection, or vasectomy) allows sperm antigens to enter the systemic circulation, leading to the formation of **anti-sperm antibodies**, a cause of male infertility. * **Option D (Correct Statement):** The formation of the BTB is a property of the Sertoli cells themselves. Studies have shown that the barrier can form even in the absence of germ cells (e.g., in "Sertoli cell-only" models), although germ cells are required for its maintenance and regulation. **Clinical Pearls for NEET-PG:** * **Location:** The BTB is located near the basement membrane of the seminiferous tubule. * **Function:** It creates an **immunologically privileged site** and maintains a unique chemical environment (high $K^+$, high Androgen Binding Protein) for sperm maturation. * **Spermatogonia vs. Spermatocytes:** Spermatogonia are located in the **basal compartment** (outside the barrier), while primary spermatocytes move through the barrier into the **adluminal compartment** to undergo meiosis.

Question 265: In the absence of pregnancy, for how many days does the corpus luteum function?

A. 8 to 10 days
B. 10 to 12 days
C. 12 to 14 days (Correct Answer)
D. 18 to 20 days

Explanation: **Explanation** The correct answer is **12 to 14 days (Option C)**. **Underlying Medical Concept:** The menstrual cycle consists of a variable follicular phase and a remarkably constant **luteal phase**. Following ovulation, the remains of the Graafian follicle transform into the **corpus luteum** under the influence of Luteinizing Hormone (LH). The corpus luteum functions as a temporary endocrine gland, secreting progesterone and estrogen to prepare the endometrium for implantation. In a non-pregnant cycle, the corpus luteum has a fixed lifespan of approximately **12 to 14 days**. If fertilization does not occur, the lack of Human Chorionic Gonadotropin (hCG) leads to **luteolysis** (degeneration of the corpus luteum into the corpus albicans). This causes a sharp drop in progesterone levels, triggering menstruation. **Analysis of Incorrect Options:** * **A & B (8 to 12 days):** While the corpus luteum reaches its peak functional activity around day 8–9 post-ovulation, it does not undergo complete involution this early in a healthy cycle. * **D (18 to 20 days):** This duration is too long. A functional corpus luteum beyond 14 days usually indicates the presence of hCG from a developing trophoblast (pregnancy). **High-Yield NEET-PG Pearls:** * **Constant Phase:** The luteal phase is the most constant part of the menstrual cycle (14 days). Variations in cycle length (e.g., a 35-day cycle) are due to variations in the **follicular phase**. * **Rescue Mechanism:** In pregnancy, **hCG** (an LH analog) "rescues" the corpus luteum, maintaining it until the placenta takes over progesterone production (the luteal-placental shift) at approximately 7–9 weeks of gestation. * **Hormone of Maintenance:** Progesterone is the primary hormone secreted by the corpus luteum.

Question 266: What is the normal pH of the vagina in an adult woman?

A. 4.5 (Correct Answer)
B. 6.5
C. 7.5
D. 7.0

Explanation: **Explanation:** The normal vaginal pH in a healthy adult woman of reproductive age is acidic, typically ranging from **3.8 to 4.5**. **Why 4.5 is correct:** The acidity is primarily maintained by **Döderlein’s bacilli** (Lactobacillus species). These bacteria colonize the vaginal epithelium under the influence of estrogen. Estrogen causes the accumulation of **glycogen** in the vaginal squamous cells. Lactobacilli ferment this glycogen into **lactic acid**, which lowers the pH. This acidic environment serves as a critical innate immune mechanism, inhibiting the growth of pathogenic bacteria and fungi. **Why other options are incorrect:** * **B (6.5):** This is near-neutral. Such a high pH is seen in prepubertal girls and postmenopausal women due to low estrogen levels and lack of glycogen. * **C (7.5) & D (7.0):** These represent alkaline or neutral states. Vaginal pH becomes more alkaline during menstruation (due to blood), in the presence of semen, or in specific infections like Trichomoniasis or Bacterial Vaginosis. **High-Yield Clinical Pearls for NEET-PG:** * **Amsel’s Criteria:** A vaginal pH **>4.5** is a key diagnostic criterion for **Bacterial Vaginosis (BV)**. * **Candidiasis:** Notably, the pH remains **normal (<4.5)** in Vulvovaginal Candidiasis, helping differentiate it from BV and Trichomoniasis. * **Estrogen Dependency:** The acidic pH is absent before puberty and after menopause because the vaginal epithelium is thin and glycogen-poor.

Question 267: In which part of the male reproductive tract do sperms gain motility?

A. Prostate
B. Seminal vesicles
C. Epididymis (Correct Answer)
D. Vas deferens

Explanation: **Explanation:** The correct answer is **C. Epididymis**. **Why it is correct:** Spermatogenesis occurs in the seminiferous tubules, but the resulting spermatozoa are morphologically complete yet **immotile** and incapable of fertilization. As they pass through the epididymis (a process taking about 12–26 days), they undergo **physiological maturation**. During this transit, biochemical changes occur in the sperm membrane, and they acquire **progressive motility**. This maturation is androgen-dependent. **Why the other options are incorrect:** * **Prostate (A):** The prostate gland secretes a thin, milky, alkaline fluid that helps neutralize the acidity of the vaginal tract and enhances sperm motility *after* ejaculation, but it is not where motility is first acquired. * **Seminal vesicles (B):** These produce a fructose-rich fluid that provides energy for sperm and prostaglandins that aid in cervical mucus penetration. They contribute to the bulk of the semen but are not the site of maturation. * **Vas deferens (D):** This serves primarily as a storage site and a conduit for transporting sperm from the epididymis to the ejaculatory ducts. **High-Yield Facts for NEET-PG:** * **Decapacitation:** While sperms gain the *ability* to move in the epididymis, they are kept in a checked state by inhibitory factors (decapacitation) until they enter the female reproductive tract. * **Capacitation:** This is the final step of maturation occurring in the **female reproductive tract** (specifically the uterus/fallopian tubes), where the glycoprotein coat is removed, leading to hyperactivated motility and the acrosome reaction. * **Storage:** The majority of sperm are stored in the **vas deferens** (not just the epididymis), maintaining fertility for several weeks.

Question 268: Gonadal sex of the fetus is determined by:

A. Secretion of testosterone
B. Secretion of anti-Müllerian hormone
C. Sex-determining region on the 'Y' chromosome (Correct Answer)
D. Secretion of estrogen

Explanation: ### Explanation The sexual differentiation of a fetus occurs in a sequential, hierarchical manner: **Genetic Sex → Gonadal Sex → Phenotypic Sex.** **1. Why the correct answer is right:** **Gonadal sex** refers to whether the undifferentiated bipotential gonads develop into testes or ovaries. This is determined by the presence or absence of the **SRY gene (Sex-determining Region on the Y chromosome)**. * If the SRY gene is present (normally on the Y chromosome), it encodes for the **Testis-Determining Factor (TDF)**, which triggers the medulla of the bipotential gonad to differentiate into **testes**. * In the absence of the SRY gene (as in 46,XX), the cortex of the gonad develops into **ovaries**. **2. Why the incorrect options are wrong:** * **Options A & B (Testosterone and AMH):** These hormones are secreted *by* the fetal testes (Leydig and Sertoli cells, respectively) *after* gonadal sex has already been established. They are responsible for determining **Phenotypic Sex** (internal and external genitalia), not gonadal sex. * **Option D (Estrogen):** Female phenotypic development is largely the "default" pathway and does not require the secretion of fetal estrogen for the initial determination of gonadal sex. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Genetic Sex:** Established at fertilization (XX or XY). * **Timing:** Gonadal differentiation begins around the **6th–7th week** of gestation. * **Sertoli Cells:** Secretes **Anti-Müllerian Hormone (AMH)**, which causes regression of Müllerian ducts (paramesonephric ducts). * **Leydig Cells:** Secretes **Testosterone**, which stimulates the development of Wolffian ducts (mesonephric ducts) into the male internal genitalia (Epididymis, Vas deferens, Seminal vesicles). * **Dihydrotestosterone (DHT):** Responsible for the development of male **external** genitalia (penis and scrotum).

Question 269: Following delivery, when does maximal milk output typically occur in the mother?

A. 3 months
B. 5 months (Correct Answer)
C. 9 months
D. 12 months

Explanation: **Explanation:** The correct answer is **5 months (Option B)**. The physiology of lactation involves a transition from colostrum (first 2–3 days) to transitional milk, and finally to mature milk. While milk production begins immediately after the withdrawal of placental steroids (estrogen and progesterone) post-delivery, the volume of milk output is not static. It gradually increases to meet the growing nutritional demands of the infant. Physiological studies on lactational performance indicate that milk production typically peaks around **5 to 6 months** postpartum. At this stage, the infant’s caloric requirements are at their highest before the significant introduction of complementary feeding (weaning). On average, a healthy mother produces approximately 700–800 ml of milk per day during this peak period. **Analysis of Incorrect Options:** * **A. 3 months:** While milk production is well-established and high, it has not yet reached the physiological peak required for a larger 5-month-old infant. * **C & D. 9 and 12 months:** By this time, "weaning" has usually commenced. As the infant consumes more solid foods, the frequency of suckling decreases. Since milk production is a demand-supply mechanism regulated by **prolactin** and the **milk-ejection reflex (oxytocin)**, reduced suckling leads to a gradual decline in output. **High-Yield NEET-PG Pearls:** * **Prolactin:** Responsible for milk **production** (secreted by anterior pituitary). * **Oxytocin:** Responsible for milk **ejection/let-down** (secreted by posterior pituitary). * **Lactational Amenorrhea:** High prolactin levels inhibit **GnRH** secretion, leading to suppressed FSH/LH and temporary infertility. * **Suckling Stimulus:** The most important factor for maintaining milk production; it triggers both prolactin and oxytocin release.

Question 270: During early pregnancy, which hormone is secreted by trophoblastic cells to maintain the corpus luteum?

A. Estrogen
B. Human chorionic gonadotropin (hCG) (Correct Answer)
C. Luteinizing hormone (LH)
D. Progesterone

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The corpus luteum of the menstrual cycle has a limited lifespan of about 12–14 days. To maintain a pregnancy, the corpus luteum must be "rescued" to continue secreting progesterone, which supports the endometrium. Following implantation, the **syncytiotrophoblast** cells of the blastocyst secrete **Human Chorionic Gonadotropin (hCG)**. hCG is a glycoprotein that is structurally and functionally similar to Luteinizing Hormone (LH). It binds to LH receptors on the corpus luteum, preventing its involution and converting it into the **corpus luteum of pregnancy**. This ensures a continuous supply of progesterone until the placenta takes over steroidogenesis (the luteal-placental shift) around the 8th–10th week. **2. Why the Incorrect Options are Wrong:** * **Estrogen (A):** While estrogen levels rise during pregnancy, it is a product of the corpus luteum and placenta, not the primary signal that maintains the corpus luteum itself. * **Luteinizing Hormone (LH) (C):** Although LH maintains the corpus luteum during a normal cycle, its levels drop during pregnancy due to negative feedback from high progesterone. hCG acts as an "LH-substitute" because it has a much longer half-life. * **Progesterone (D):** Progesterone is the *result* of corpus luteum stimulation, not the *stimulus* for its maintenance. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Detection:** hCG can be detected in maternal blood as early as **8–9 days after ovulation** (shortly after implantation). * **Doubling Time:** In early normal pregnancy, hCG levels double approximately every **48 hours**. * **Subunits:** hCG has an $\alpha$ and $\beta$ subunit. The **$\beta$-subunit** is unique and is what pregnancy tests (UDT/Serum) measure to avoid cross-reactivity with TSH, FSH, and LH. * **Peak Levels:** hCG levels peak at approximately **10–12 weeks** of gestation and then decline to a lower plateau.

Practice by Chapter

Male Reproductive Physiology

Practice Questions

Spermatogenesis and Sperm Function

Practice Questions

Female Reproductive Physiology

Practice Questions

Menstrual Cycle

Practice Questions

Ovulation and Fertilization

Practice Questions

Physiology of Pregnancy

Practice Questions

Parturition

Practice Questions

Lactation

Practice Questions

Sexual Differentiation and Development

Practice Questions

Reproductive Aging

Practice Questions

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