Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 61: The corpus luteum functions maximally for how many days in the absence of implantation?

A. 9 (Correct Answer)
B. 12
C. 6
D. 15

Explanation: **Explanation:** The lifespan of the corpus luteum (CL) is the defining feature of the luteal phase of the menstrual cycle. Following ovulation (typically Day 14), the ruptured follicle transforms into the corpus luteum under the influence of Luteinizing Hormone (LH). **Why 9 days is correct:** In a non-pregnant cycle, the corpus luteum reaches its **peak functional activity** (maximal secretion of progesterone and estrogen) approximately **7 to 9 days after ovulation**. If fertilization and implantation do not occur, the lack of Human Chorionic Gonadotropin (hCG) leads to "luteolysis." The CL begins to regress around Day 22-23 of a 28-day cycle, meaning it functions at its maximum capacity for roughly **9 days** before undergoing involution into the corpus albicans. **Analysis of Incorrect Options:** * **6 days:** This is too early; the CL is still developing and increasing its vascularity and hormone production during this period. * **12 days:** While the total luteal phase lasts about 14 days, the CL starts degenerating by day 10-12 in the absence of hCG. It is not functioning "maximally" at this late stage. * **15 days:** This exceeds the standard 14-day luteal phase. Without implantation, the CL cannot sustain function for 15 days due to the programmed drop in LH support. **NEET-PG High-Yield Pearls:** * **The "Rescue" Mechanism:** If implantation occurs, the syncytiotrophoblast secretes **hCG**, which mimics LH and "rescues" the corpus luteum, extending its life for 8–10 weeks until the placenta takes over (Luteal-Placental shift). * **Fixed Duration:** While the follicular phase varies, the **luteal phase is constant at 14 days**. * **Hormone Profile:** Progesterone is the dominant hormone of the luteal phase; its withdrawal is the primary trigger for menstruation.

Question 62: Which is the most potent estrogen?

A. Estrone
B. Estradiol (Correct Answer)
C. Estriol
D. Etisterone enanthate

Explanation: **Explanation:** The potency of endogenous estrogens is determined by their affinity for estrogen receptors (ERα and ERβ). **1. Why Estradiol is correct:** **Estradiol (E2)** is the most potent and dominant estrogen produced by the ovaries during the reproductive years. It has the highest binding affinity for estrogen receptors, being approximately **10 times more potent than estrone** and **80-100 times more potent than estriol**. It is primarily synthesized in the granulosa cells of the ovarian follicles via the aromatization of androstenedione and testosterone. **2. Why other options are incorrect:** * **Estrone (E1):** This is a "weak" estrogen. It is the primary estrogen after menopause, formed mainly through the peripheral conversion of adrenal androstenedione in adipose tissue. * **Estriol (E3):** This is the "weakest" naturally occurring estrogen. It is produced in significant quantities by the **placenta** during pregnancy. High levels of E3 are a marker of fetal-placental well-being. * **Ethisterone enanthate:** This is a synthetic progestogen (not a natural estrogen) and is not relevant to the hierarchy of endogenous estrogen potency. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Hierarchy:** Estradiol (E2) > Estrone (E1) > Estriol (E3). * **Source Mnemonic:** * **E1** (On-e) → Menopause (Primary source: Adipose). * **E2** (Di-ol) → Ovaries (Dominant in reproductive age). * **E3** (Tri-ol) → Pregnancy (Primary source: Placenta). * **Aromatase** is the key enzyme that converts androgens to estrogens. * **Estriol** is often used as a marker in the Triple/Quadruple screen for Down Syndrome (where it is characteristically low).

Question 63: What is the two-gonadotropin hypothesis?

A. FSH and LH inhibit the release of estrogen and progesterone.
B. FSH acts on granulosa cells and LH acts on theca cells. (Correct Answer)
C. FSH stimulates estrogen production, while LH inhibits estrogen production.
D. FSH provides negative feedback to the hypothalamus, while LH provides negative feedback to the pituitary.

Explanation: The **Two-Cell, Two-Gonadotropin Hypothesis** describes the synergistic relationship between theca and granulosa cells in the ovarian follicle to produce estradiol. ### Why Option B is Correct The production of estrogen requires two distinct cell types and two different gonadotropins: 1. **Theca Cells (LH):** LH stimulates theca cells to convert cholesterol into **androgens** (androstenedione and testosterone). Theca cells lack the enzyme *aromatase*, so they cannot produce estrogen themselves. 2. **Granulosa Cells (FSH):** FSH stimulates granulosa cells to take up the androgens produced by theca cells. Under the influence of FSH, the enzyme **aromatase** converts these androgens into **estradiol**. Granulosa cells lack the enzymes necessary to synthesize androgens from cholesterol, making them dependent on theca cells. ### Why Other Options are Incorrect * **Option A:** FSH and LH *stimulate* (rather than inhibit) the synthesis of estrogen and progesterone. * **Option C:** Both FSH and LH are essential for estrogen production; LH provides the precursor (androgen), and FSH facilitates the final conversion. * **Option D:** Estrogen and progesterone provide feedback to the hypothalamus and pituitary; the gonadotropins themselves are the effectors, not the primary feedback signals in this context. ### High-Yield NEET-PG Pearls * **Mnemonic:** **L**H acts on **L**evel 1 (Theca - outer) to make androgens; **F**SH acts on **F**actory (Granulosa - inner) to finish the product. * **Enzyme Key:** Theca cells have **17α-hydroxylase** (needed for androgens); Granulosa cells have **Aromatase** (needed for estrogens). * **Clinical Correlation:** In PCOS, an elevated LH:FSH ratio leads to excess androgen production by theca cells, which cannot be fully converted to estrogen, resulting in hyperandrogenism.

Question 64: Which of the following is NOT true about nocturnal penile tumescence?

A. It totals about 100 minutes per night.
B. It is a normal phenomenon. (Correct Answer)
C. It occurs in NREM sleep.
D. It can be used to distinguish between psychological or organic impotence.

Explanation: **Explanation:** **Nocturnal Penile Tumescence (NPT)** is a spontaneous erection occurring during sleep. The question asks for the statement that is **NOT true**. However, there appears to be a discrepancy in the provided key: **Option B ("It is a normal phenomenon") is actually a TRUE statement.** In the context of NEET-PG, the **incorrect** statement (and thus the intended answer for "NOT true") is **Option C**. 1. **Why Option C is the intended answer (The "NOT true" statement):** NPT is physiologically linked to **REM (Rapid Eye Movement) sleep**, not NREM sleep. During REM sleep, there is a withdrawal of noradrenergic tone and an activation of cholinergic pathways, leading to vasodilation and erection. A healthy male typically experiences 3 to 5 episodes of NPT per night, coinciding with REM cycles. 2. **Analysis of other options:** * **Option A:** True. In a healthy young adult, the cumulative duration of NPT episodes totals approximately **100 minutes** per night. * **Option B:** True. NPT is a **normal physiological phenomenon** seen in healthy males from infancy to old age. * **Option C:** False. As explained, it occurs during **REM sleep**. * **Option D:** True. This is the primary clinical utility of NPT. If a patient has erectile dysfunction (ED) but still experiences normal NPT, the cause is likely **psychogenic**. If NPT is absent, the cause is likely **organic** (vascular, neurological, or endocrine). **High-Yield Clinical Pearls for NEET-PG:** * **Stamp Test/Rigiscan:** These are tools used to monitor NPT to differentiate between organic and psychogenic impotence. * **Mechanism:** Mediated by the release of Nitric Oxide (NO) and cyclic GMP, leading to smooth muscle relaxation in the corpus cavernosum. * **REM Sleep Association:** Remember the mnemonic: **"REM = Rapid Erection Movement"** to link NPT with the correct sleep stage.

Question 65: According to the World Health Organization 2010 strict criteria for semen analysis morphology, what percentage of normal forms is considered indicative?

A. >15% normal forms
B. >=4% normal forms (Correct Answer)
C. >=25% normal forms
D. >=32% normal forms

Explanation: ### Explanation The correct answer is **B. >=4% normal forms**. This question tests knowledge of the **WHO Laboratory Manual for the Examination and Processing of Human Semen (5th Edition, 2010)**, which introduced the "Kruger’s Strict Criteria" for assessing sperm morphology. #### Why Option B is Correct: Under the 2010 WHO criteria, the lower reference limit for **normal forms is 4%** (5th percentile). This "strict" assessment requires the sperm to have a perfectly smooth, oval head, a well-defined acrosome (occupying 40–70% of the head), and no neck, midpiece, or tail defects. Even minor irregularities classify the sperm as "abnormal." #### Why Other Options are Incorrect: * **Option A (>15%):** This was the cutoff used in the **1992 (3rd Edition)** WHO criteria. It is now considered outdated. * **Option C (>=25%):** This value does not correspond to any standard WHO threshold for morphology. * **Option D (>=32%):** This is the WHO 2010 lower reference limit for **Progressive Motility (PR)**, not morphology. #### High-Yield Clinical Pearls for NEET-PG: To master semen analysis questions, remember these **WHO 2010 Reference Values**: 1. **Volume:** ≥1.5 mL 2. **Total Sperm Count:** ≥39 million per ejaculate 3. **Sperm Concentration:** ≥15 million/mL 4. **Total Motility (PR + NP):** ≥40% 5. **Progressive Motility (PR):** ≥32% 6. **Vitality (Live Sperm):** ≥58% 7. **Morphology:** ≥4% normal forms **Note:** The 6th Edition (2021) maintains the 4% morphology threshold but has slightly updated other parameters (e.g., volume to 1.4 mL); however, the 2010 criteria remain the most frequently tested in exams.

Question 66: Resolution of corpus luteum occurs because of:

A. Increased levels of progesterone
B. Increased levels of estrogen
C. Decreased levels of LH (Correct Answer)
D. Decreased levels of FSH

Explanation: **Explanation:** The **corpus luteum (CL)** is a temporary endocrine structure formed from the empty follicle after ovulation. Its primary function is to secrete high levels of progesterone and moderate levels of estrogen to prepare the endometrium for implantation. **Why Option C is Correct:** The survival and maintenance of the corpus luteum are strictly dependent on **Luteinizing Hormone (LH)**. LH provides the necessary "luteotropic" support. After ovulation, if fertilization does not occur, the high levels of progesterone and estrogen exert **negative feedback** on the anterior pituitary, leading to a significant **decrease in LH secretion**. Without the trophic support of LH, the corpus luteum cannot sustain itself, leading to its involution (luteolysis) and subsequent transformation into the fibrous *corpus albicans*. **Why Other Options are Incorrect:** * **Options A & B:** Increased levels of progesterone and estrogen are the *products* of the corpus luteum, not the cause of its resolution. While they indirectly cause resolution via negative feedback on LH, the direct physiological trigger for luteolysis is the withdrawal of LH support. * **Option D:** While FSH levels also decline during the luteal phase due to inhibin and steroid feedback, FSH is primarily responsible for follicular recruitment and growth, not the maintenance of the corpus luteum. **High-Yield NEET-PG Pearls:** * **Rescue of Corpus Luteum:** If pregnancy occurs, the syncytiotrophoblast secretes **hCG (human Chorionic Gonadotropin)**. hCG is structurally similar to LH and binds to LH receptors, "rescuing" the corpus luteum from degradation until the placenta takes over progesterone production (the luteal-placental shift at ~7–9 weeks). * **Luteolysis Trigger:** In humans, luteolysis is primarily an intra-ovarian process triggered by LH withdrawal, unlike in many mammals where uterine Prostaglandin F2α (PGF2α) is the primary luteolytic agent.

Question 67: What type of cell division is responsible for the early phase division of spermatogonia?

A. Meiosis
B. Mitosis (Correct Answer)
C. Both Meiosis and Mitosis
D. Maturation

Explanation: **Explanation:** The correct answer is **Mitosis**. **Why Mitosis is correct:** Spermatogenesis begins with **spermatogonia** (diploid stem cells, 46 XY) located on the basement membrane of the seminiferous tubules. In the early phase, these cells undergo **mitotic division** to serve two purposes: 1. **Self-renewal:** Maintaining the stem cell population (Type A spermatogonia). 2. **Proliferation:** Producing cells destined to become sperm (Type B spermatogonia). Since the goal of this stage is to increase the cell count while maintaining a full diploid complement of chromosomes, mitosis is the required mechanism. **Why other options are incorrect:** * **Meiosis:** This occurs later in the process. Only **Primary Spermatocytes** undergo Meiosis I (to become secondary spermatocytes) and Meiosis II (to become spermatids) to achieve haploidy (23 chromosomes). * **Both Meiosis and Mitosis:** While both occur during the *entire* process of spermatogenesis, the question specifically asks for the **early phase division of spermatogonia**, which is exclusively mitotic. * **Maturation:** This refers to **Spermiogenesis**, the morphological transformation of a spherical spermatid into a motile spermatozoon. It involves no cell division. **High-Yield Clinical Pearls for NEET-PG:** * **Spermatogonia to Spermatozoa:** The entire process takes approximately **74 days**. * **Blood-Testis Barrier:** Formed by **Sertoli cells** (tight junctions). It protects germ cells from the immune system, starting at the primary spermatocyte stage. * **Spermiation:** The process by which mature spermatozoa are released from Sertoli cells into the lumen of the seminiferous tubules. * **Chromosome Count:** Remember: Spermatogonia (46), Primary Spermatocyte (46), Secondary Spermatocyte (23), Spermatid (23).

Question 68: What is considered the normal sperm count?

A. 20 million per ml
B. 40 million per ejaculate
C. Both (Correct Answer)
D. None

Explanation: **Explanation:** The assessment of male fertility is based on the **WHO Laboratory Manual for the Examination and Processing of Human Semen (6th Edition, 2021)**. The correct answer is **Both** because normal semen parameters are defined by two distinct but related metrics: concentration and total count. 1. **Sperm Concentration (Option A):** This refers to the number of spermatozoa per unit volume. The lower reference limit is **15–20 million per ml**. Values below this are termed *Oligozoospermia*. 2. **Total Sperm Number (Option B):** This refers to the total number of spermatozoa in the entire ejaculate. The lower reference limit is **39–40 million per ejaculate**. This is calculated by multiplying the concentration by the total semen volume. **Why other options are incorrect:** * **Option A & B individually:** While both are correct, selecting only one would be incomplete. Clinical evaluation requires both parameters to be met to ensure adequate fertility potential. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Semen Volume:** 1.5 to 5.0 ml. * **Azoospermia:** Complete absence of sperm in the ejaculate. * **Aspermia:** Complete absence of semen (no ejaculate). * **Asthenozoospermia:** Reduced sperm motility (Normal: ≥40% total motility or ≥32% progressive motility). * **Teratozoospermia:** Reduced percentage of morphologically normal sperm (Normal: ≥4% by Kruger’s strict criteria). * **Fructose:** Produced by seminal vesicles; its absence suggests bilateral congenital absence of the vas deferens or ejaculatory duct obstruction.

Question 69: Erection is associated with all the following except?

A. Sacral plexus
B. Hypogastric plexus
C. Pudendal nerves (Correct Answer)
D. Nervi erigentes

Explanation: The physiological process of penile erection is primarily a **parasympathetic (autonomic)** event, whereas the **pudendal nerve** is a **somatic** nerve. ### Why Pudendal Nerve is the Correct Answer (The "Except") The **pudendal nerve (S2–S4)** provides somatic motor and sensory innervation. While it is responsible for the sensory perception of stimuli and the contraction of the bulbospongiosus and ischiocavernosus muscles during ejaculation and the maintenance of an erection, it does **not** initiate the vascular changes (vasodilation) required for an erection. Erection is mediated by the autonomic nervous system. ### Explanation of Other Options * **Sacral Plexus (S2–S4):** This is the anatomical origin of the preganglionic parasympathetic fibers that control erection. * **Hypogastric Plexus:** While the Superior Hypogastric Plexus is primarily sympathetic (mediating emission), the **Inferior Hypogastric Plexus (Pelvic Plexus)** contains the relay centers where parasympathetic fibers from the sacral cord synapse before heading to the cavernous tissue. * **Nervi Erigentes:** These are the **pelvic splanchnic nerves**. They carry parasympathetic outflow from S2–S4. Upon stimulation, they release Nitric Oxide (NO) and Acetylcholine, causing relaxation of the smooth muscles of the corpora cavernosa and vasodilation of the helicine arteries, leading to tumescence. ### High-Yield Clinical Pearls for NEET-PG * **Mnemonic "Point and Shoot":** **P**arasympathetic = **P**oint (Erection); **S**ympathetic = **S**hoot (Emission/Ejaculation). * **Neurotransmitter:** Nitric Oxide (NO) is the most important mediator of erection; it increases cGMP, leading to smooth muscle relaxation. * **Sildenafil (Viagra):** Acts by inhibiting Phosphodiesterase-5 (PDE-5), preventing the breakdown of cGMP. * **Ejaculation Reflex:** Emission is mediated by the **Hypogastric nerve** (Sympathetic, T12–L2), while forceful ejaculation is mediated by the **Pudendal nerve** (Somatic).

Question 70: All of the following are true regarding the LH surge except:

A. The LH surge acts rapidly on both granulosa and theca cells of the preovulatory follicle.
B. The LH surge initiates re-entry of the oocyte into meiosis.
C. Ovulation occurs 24 hours after the LH surge. (Correct Answer)
D. The mean duration of the LH surge is 48 hours.

Explanation: **Explanation** The LH surge is the critical hormonal trigger for ovulation and the transition from the follicular to the luteal phase. **Why Option C is the correct (False) statement:** Ovulation does not occur exactly 24 hours after the LH surge begins. In clinical physiology, ovulation typically occurs **32 to 36 hours** after the onset of the LH surge and approximately **10 to 12 hours** after the LH peak. A 24-hour timeline is more characteristic of the interval following the **estradiol peak**, not the LH surge itself. **Analysis of other options:** * **Option A:** LH receptors are present on both theca cells (always) and mature granulosa cells (induced by FSH). The surge rapidly triggers luteinization and progesterone production in both cell types. * **Option B:** The LH surge terminates the action of Oocyte Maturation Inhibitor (OMI), allowing the primary oocyte to resume **Meiosis I** (completing it just before ovulation) and progress to Meiosis II, where it arrests in metaphase. * **Option D:** The mean duration of the LH surge is approximately **48 hours**. It typically features a rising limb (14 hours), a plateau (14 hours), and a falling limb (20 hours). **High-Yield NEET-PG Pearls:** * **Trigger:** The LH surge is triggered by a "positive feedback" loop when plasma estradiol levels exceed **200 pg/mL** for at least **36–48 hours**. * **Enzymatic Action:** LH stimulates prostaglandins, plasminogen activator, and collagenase, which weaken the follicular wall (stigma) to allow rupture. * **Urine Testing:** Home ovulation kits detect the LH surge in urine; ovulation usually follows 12–24 hours after a positive urine test (as urine lags behind blood levels).

Practice by Chapter

Male Reproductive Physiology

Practice Questions

Spermatogenesis and Sperm Function

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Female Reproductive Physiology

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Menstrual Cycle

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Ovulation and Fertilization

Practice Questions

Physiology of Pregnancy

Practice Questions

Parturition

Practice Questions

Lactation

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Sexual Differentiation and Development

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Reproductive Aging

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