Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 301: The production of estradiol by the testes requires:

A. Sertoli cell follistatin
B. LH and Leydig cells
C. Activin but not LH
D. Leydig cells, Sertoli cells, LH, and FSH (Correct Answer)

Explanation: **Explanation:** The production of estradiol in the testes follows a **two-cell, two-gonadotropin mechanism**, analogous to the process in the ovaries. This synergy requires the cooperation of both Leydig and Sertoli cells under the influence of LH and FSH. 1. **Leydig Cells & LH:** Luteinizing Hormone (LH) stimulates Leydig cells to produce **testosterone** from cholesterol. 2. **Sertoli Cells & FSH:** Follicle-Stimulating Hormone (FSH) stimulates Sertoli cells to produce the enzyme **aromatase**. 3. **The Process:** Testosterone produced by the Leydig cells diffuses into the adjacent Sertoli cells. Here, under the influence of FSH-induced aromatase, testosterone is converted into **estradiol**. Thus, all four components—Leydig cells, Sertoli cells, LH, and FSH—are essential for testicular estrogen synthesis. **Analysis of Incorrect Options:** * **Option A:** Follistatin is a protein that binds and neutralizes activin; while present in the testes, it is not the primary driver of steroidogenesis. * **Option B:** While LH and Leydig cells provide the precursor (testosterone), they lack significant aromatase activity to complete the conversion to estradiol on their own. * **Option C:** Activin stimulates FSH secretion but cannot replace the requirement for LH-driven androgen production. **High-Yield NEET-PG Pearls:** * **Aromatase Location:** In adult males, about 20% of estradiol is produced directly in the testes (Sertoli cells), while 80% is produced by peripheral aromatization of testosterone in adipose tissue and the liver. * **Blood-Testis Barrier:** Sertoli cells form this barrier via tight junctions, protecting developing germ cells. * **Inhibin B:** Produced by Sertoli cells, it provides negative feedback specifically to FSH.

Question 302: What is the main source of production of relaxin?

A. Ovary (Correct Answer)
B. Placenta
C. Decidua
D. Adrenals

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Relaxin is a polypeptide hormone belonging to the insulin family. In humans, the **corpus luteum of the ovary** is the primary and most significant source of relaxin production. During the menstrual cycle, it is secreted by the corpus luteum in the luteal phase, but its levels rise significantly during pregnancy. Its primary role is to relax the pelvic ligaments, soften the cervix, and inhibit uterine contractions to maintain pregnancy. **2. Why the Other Options are Incorrect:** * **Placenta:** While the placenta does produce small amounts of relaxin, it is not the *main* source in humans. Its contribution is secondary to the corpus luteum. * **Decidua:** The decidua (the modified uterine lining during pregnancy) also expresses relaxin mRNA and secretes minor amounts, but this acts primarily in a paracrine/local fashion rather than being the systemic primary source. * **Adrenals:** The adrenal glands do not produce relaxin; they are responsible for steroid hormones (cortisol, aldosterone) and catecholamines. **3. High-Yield Clinical Pearls for NEET-PG:** * **Peak Levels:** Relaxin levels peak during the **first trimester** (around 14 weeks) and again at delivery. * **Mechanism:** It acts by increasing the water content of the cervix and collagen remodeling, which facilitates "cervical ripening." * **Male Source:** In males, relaxin is produced by the **prostate gland** and is found in seminal fluid, where it helps in sperm motility. * **Receptors:** It acts via G-protein coupled receptors (LGR7 and LGR8). * **Key Function:** It works synergistically with progesterone to maintain uterine quiescence early in pregnancy.

Question 303: During sexual differentiation in males, what occurs?

A. Leydig cells produce Mullerian Inhibiting Substance.
B. Primitive gonads differentiate into testes due to the presence of the SRY gene. (Correct Answer)
C. Androgen binding protein is responsible for the development of male external genitalia.
D. The Wolffian duct regresses.

Explanation: ### Explanation **1. Why the Correct Answer is Right:** Sexual differentiation is a sequential process. The fundamental step in male development is the presence of the **SRY gene** (Sex-determining Region on the Y chromosome). This gene encodes for the **Testis-Determining Factor (TDF)**. Around the 6th–7th week of gestation, TDF acts on the bipotential/primitive gonads, directing them to differentiate into **testes**. Without the SRY gene, the default pathway leads to the development of ovaries. **2. Why the Incorrect Options are Wrong:** * **Option A:** **Sertoli cells** (not Leydig cells) produce Mullerian Inhibiting Substance (MIS), also known as Anti-Mullerian Hormone (AMH). Leydig cells are responsible for producing Testosterone. * **Option C:** The development of male external genitalia (penis and scrotum) is mediated by **Dihydrotestosterone (DHT)**, which is converted from testosterone by the enzyme 5-alpha reductase. Androgen Binding Protein (ABP) serves to maintain high local concentrations of testosterone within the seminiferous tubules for spermatogenesis. * **Option D:** In males, the **Wolffian duct persists** and differentiates into the epididymis, vas deferens, and seminal vesicles under the influence of testosterone. It is the Mullerian duct that regresses (due to MIS). **3. NEET-PG High-Yield Pearls:** * **"Default" Sex:** Female is the default phenotypic sex; male differentiation requires active hormonal intervention. * **Internal vs. External:** Testosterone = Internal male genitalia (Wolffian); DHT = External male genitalia. * **Swyer Syndrome:** A 46,XY individual with a mutation in the SRY gene, resulting in streak gonads and female phenotype. * **Mullerian Agenesis (MRKH):** 46,XX with normal ovaries but absent uterus/upper vagina (often confused with Androgen Insensitivity Syndrome).

Question 304: During which phase of the human sexual response cycle is it physiologically impossible for males to achieve erection or orgasm?

A. Excitement Phase
B. Plateau Phase
C. Orgasm
D. Resolution (Correct Answer)

Explanation: **Explanation:** The human sexual response cycle, as described by Masters and Johnson, consists of four phases: Excitement, Plateau, Orgasm, and Resolution. The **Resolution Phase** is the correct answer because it is characterized by the **Refractory Period** in males. This is a physiological interval immediately following orgasm during which it is impossible to achieve another erection or ejaculation, regardless of the level of stimulation. This occurs due to the release of **prolactin**, which inhibits dopamine (the primary driver of sexual arousal), and the dominance of the sympathetic nervous system, which causes vasoconstriction and detumescence. **Analysis of Incorrect Options:** * **Excitement Phase:** This is the initial stage where parasympathetic stimulation leads to vasocongestion and the *initiation* of an erection. * **Plateau Phase:** This is the period of intensified sexual tension preceding orgasm. Erection is maintained and reaches its peak during this stage. * **Orgasm:** This is the climax of the cycle, characterized by rhythmic contractions of the pelvic musculature and ejaculation. It is the event that *triggers* the subsequent refractory period, but is not the period of physiological impossibility itself. **High-Yield Facts for NEET-PG:** * **Refractory Period:** Only occurs in males. Females are physiologically capable of multiple orgasms without a mandatory refractory interval. * **Neurobiology:** Parasympathetic nerves (S2-S4) mediate **E**rection ("**P**oint"), while Sympathetic nerves (T11-L2) mediate **E**jaculation ("**S**hoot"). * **Prolactin's Role:** Elevated prolactin levels post-orgasm are responsible for the "sexual satiety" and the duration of the refractory period. Pathological hyperprolactinemia (e.g., prolactinoma) can lead to erectile dysfunction.

Question 305: Which of the following is NOT related to the corpus luteum?

A. Luteinised granulosa cells produce progesterone.
B. Estrogen continues to be produced by the luteinised granulosa cells.
C. Luteolysis is due to estrogen, PGF2a, and endothelin.
D. The peak steroid production is between the 23rd and 25th day. (Correct Answer)

Explanation: ### Explanation The **Corpus Luteum (CL)** is a temporary endocrine structure formed after ovulation, primarily responsible for secreting progesterone to maintain the secretory phase of the endometrium. **1. Why Option D is the Correct Answer (The Incorrect Statement):** In a standard 28-day menstrual cycle, ovulation occurs on Day 14. The corpus luteum reaches its maximum size and functional peak (highest steroid production) approximately **7 to 8 days after ovulation**, which corresponds to **Day 21 or 22** of the cycle. By Day 23–25, if fertilization has not occurred, the CL begins to undergo luteolysis (regression), and steroid levels start to decline. **2. Analysis of Other Options:** * **Option A:** After the LH surge, granulosa cells undergo "luteinization." These cells increase in size and develop the enzymatic machinery (increased cholesterol side-chain cleavage enzyme) to produce large amounts of **progesterone**. * **Option B:** While progesterone is the dominant hormone, the luteinized granulosa cells (and theca lutein cells) continue to produce **estrogen**. This creates the characteristic secondary estrogen peak seen during the mid-luteal phase. * **Option C:** Luteolysis is a complex process. Locally produced **Estrogen** (which induces PGF2α receptors), **PGF2α** (the primary luteolytic agent), and **Endothelin-1** (a potent vasoconstrictor) act in concert to cause functional and structural regression of the CL into the corpus albicans. **High-Yield Clinical Pearls for NEET-PG:** * **Life Span:** The life span of the corpus luteum is fixed at approximately **14 days** (range 12–16 days). * **Rescue:** If pregnancy occurs, **hCG** (human Chorionic Gonadotropin) from the syncytiotrophoblast rescues the CL by acting on LH receptors, maintaining it until the placenta takes over steroidogenesis (the luteal-placental shift at 7–9 weeks). * **Hormone Profile:** The luteal phase is characterized by **high Progesterone, high Estrogen, and low LH/FSH** (due to negative feedback).

Question 306: How many ovum/ova are formed from one primary oocyte?

A. 1 (Correct Answer)
B. 2
C. 3
D. 4

Explanation: **Explanation:** The process of **oogenesis** is characterized by unequal cytoplasmic division, which ensures that the resulting zygote has sufficient nutrient reserves. **Why Option A is Correct:** A single **primary oocyte** (diploid, 2n) undergoes Meiosis I to produce one **secondary oocyte** and the first polar body. The secondary oocyte then undergoes Meiosis II (completed only upon fertilization) to produce **one functional ovum** and a second polar body. The polar bodies are small, non-functional cells that eventually degenerate. Thus, the net yield from one primary oocyte is exactly **one haploid ovum**. **Why Other Options are Incorrect:** * **Options B & C:** These are incorrect because the division is asymmetrical. While four nuclei are technically produced if the first polar body divides, only one becomes a viable gamete. * **Option D:** This is a common distractor based on **spermatogenesis**. In males, one primary spermatocyte undergoes symmetrical division to produce **four functional spermatozoa**. In females, the "waste" of genetic material into polar bodies prevents the formation of four ova. **High-Yield NEET-PG Pearls:** * **Meiotic Arrests:** Oogenesis halts twice. First, in **Prophase I (Diplotene stage)** at birth, and second, in **Metaphase II** during ovulation (completed only if sperm entry occurs). * **Dictyate Stage:** The prolonged resting phase in Prophase I is also known as the Dictyate stage. * **Polar Bodies:** These serve as a mechanism to discard extra chromosomes while retaining almost all the cytoplasm in a single cell.

Question 307: Given that one secondary oocyte is produced in each menstrual cycle, how many secondary oocytes are produced on average during the reproductive life of a human female?

A. 420,000
B. 42,000
C. 4,200
D. 420 (Correct Answer)

Explanation: **Explanation:** The number of secondary oocytes produced during a woman’s reproductive life is determined by the duration of her fertility and the frequency of ovulation. **1. Why the Correct Answer (D) is Right:** The calculation is based on the average reproductive span of a human female: * **Reproductive Years:** Menarche (onset) occurs at ~12–13 years, and Menopause (cessation) occurs at ~45–50 years. This gives an average reproductive window of **35 years**. * **Cycles per Year:** With an average menstrual cycle of 28 days, a woman undergoes approximately **12–13 ovulations per year**. * **Calculation:** 35 years × 12 cycles/year = **420 secondary oocytes**. Since only one dominant follicle typically reaches the stage of ovulation (releasing a secondary oocyte) per cycle, the total number is approximately 400–450. **2. Why Incorrect Options are Wrong:** * **Option A (420,000):** This represents the approximate number of **primary oocytes** present in the ovaries at **puberty**. Most undergo atresia before ovulation. * **Option B (42,000) & C (4,200):** These are mathematically incorrect orders of magnitude that do not correlate with the physiological timeline of the human menstrual cycle. **3. High-Yield NEET-PG Pearls:** * **Oogonia Count:** At 5 months of intrauterine life, there are ~7 million oogonia. At birth, this drops to ~2 million. By puberty, only ~400,000 remain. * **Meiotic Arrest:** Primary oocytes are arrested in **Prophase I (Diplotene stage)** until puberty. The secondary oocyte is arrested in **Metaphase II** until fertilization. * **Atresia:** Over 99% of the follicles present at birth undergo a degenerative process called atresia; only ~0.1% ever ovulate.

Question 308: Ovulation occurs:

A. Before the LH surge
B. After a biphasic rise in body temperature
C. After the ripening of the follicle by FSH (Correct Answer)
D. Before the estrogen peak

Explanation: **Explanation:** **Why Option C is Correct:** Ovulation is the process where a mature (Graafian) follicle ruptures to release a secondary oocyte. This process is fundamentally dependent on the **"ripening" or maturation of the follicle**, which is primarily driven by **FSH (Follicle Stimulating Hormone)** during the follicular phase. FSH stimulates the growth of granulosa cells and the expression of LH receptors; without this FSH-mediated maturation, the follicle cannot respond to the LH surge required for ovulation. **Analysis of Incorrect Options:** * **Option A:** Ovulation occurs **after** the LH surge, not before. The LH surge is the immediate trigger for ovulation, occurring approximately 24–36 hours before the rupture of the follicle. * **Option B:** Body temperature shows a **monophasic** rise (increase of 0.5–1.0°F) **after** ovulation due to the thermogenic effect of Progesterone secreted by the corpus luteum. Therefore, ovulation occurs *before* the temperature rise. * **Option D:** Ovulation occurs **after** the estrogen peak. Estrogen levels peak approximately 24–48 hours before ovulation. This peak is essential as it exerts positive feedback on the anterior pituitary to trigger the LH surge. **High-Yield NEET-PG Pearls:** * **LH Surge:** The most reliable predictor of impending ovulation. Ovulation occurs **10–12 hours after the LH peak** and **32–36 hours after the onset of the LH surge**. * **Meiosis:** Just before ovulation, the primary oocyte completes **Meiosis I** and gets arrested in **Metaphase of Meiosis II**. * **Mittelschmerz Sign:** Pelvic pain experienced mid-cycle due to follicular rupture. * **Spinnbarkeit Phenomenon:** Under estrogen influence, cervical mucus becomes thin, watery, and stretchable just before ovulation.

Question 309: What is the diameter of a Graafian follicle at the time of ovulation?

A. 10 mm
B. 15 mm
C. 20 mm (Correct Answer)
D. 25 mm

Explanation: ### Explanation **1. Why 20 mm is the Correct Answer:** The Graafian follicle (mature tertiary follicle) is the final stage of follicular development before ovulation. Under the influence of Follicle Stimulating Hormone (FSH), a cohort of follicles begins to grow, but usually, only one becomes "dominant." This dominant follicle grows at a rate of approximately **2 mm per day** during the late follicular phase. By the time of the Luteinizing Hormone (LH) surge, it typically reaches a diameter of **18–24 mm** (average **20 mm**). At this size, it is visible on ultrasound and ready to rupture to release the secondary oocyte. **2. Why Other Options are Incorrect:** * **10 mm (Option A):** At this size, the follicle is considered a "selection-stage" follicle. While it has surpassed the size of recruited follicles, it is not yet mature enough for ovulation. * **15 mm (Option B):** This represents a growing pre-ovulatory follicle. While close to maturity, it generally requires another 2–3 days of growth to reach peak functional capacity and trigger the LH surge. * **25 mm (Option D):** While some follicles may reach this size, it is at the upper limit of normal. Follicles exceeding 25–30 mm without rupturing are often classified as follicular cysts rather than healthy ovulatory follicles. **3. NEET-PG High-Yield Pearls:** * **Growth Rate:** The dominant follicle grows **2 mm/day** in the 4–5 days preceding ovulation. * **Trigger:** Ovulation occurs approximately **10–12 hours after the LH peak** and **32–36 hours after the onset of the LH surge**. * **Stigma:** The small, avascular area that appears on the ovarian surface just before rupture is called the *stigma*. * **Clinical Correlation:** In follicular monitoring for IVF or ovulation induction, a follicle is considered "mature" and ready for an hCG trigger once it reaches **18 mm**.

Question 310: Which hormone is not affected by the menstrual cycle?

A. Estrogen
B. Progesterone
C. Gonadotropins
D. Prolactin (Correct Answer)

Explanation: **Explanation:** The menstrual cycle is governed by the rhythmic fluctuation of hormones within the Hypothalamic-Pituitary-Ovarian (HPO) axis. **Why Prolactin is the Correct Answer:** Prolactin is primarily involved in lactogenesis and is regulated by the inhibitory effect of **Dopamine** from the hypothalamus. Unlike other reproductive hormones, Prolactin levels remain relatively **stable** throughout the normal menstrual cycle in non-pregnant, non-lactating women. It does not play a direct role in the cyclical changes of the endometrium or ovulation. **Why the Other Options are Incorrect:** * **Estrogen:** Levels fluctuate significantly, peaking twice: once during the late follicular phase (triggering the LH surge) and again during the mid-luteal phase. * **Progesterone:** This hormone is cycle-dependent, with levels being very low during the follicular phase and rising sharply after ovulation (secreted by the **Corpus Luteum**) during the luteal phase. * **Gonadotropins (FSH and LH):** These pituitary hormones show dramatic variations. FSH rises at the start of the cycle to recruit follicles, and both FSH and LH exhibit a massive **pre-ovulatory surge** triggered by positive feedback from estrogen. **High-Yield Clinical Pearls for NEET-PG:** * **Prolactin & Amenorrhea:** While Prolactin doesn't change *with* the cycle, pathologically high levels (Hyperprolactinemia) inhibit GnRH pulsatility, leading to secondary amenorrhea and infertility. * **The "LH Surge":** Occurs 24–36 hours before ovulation; it is the most reliable predictor of ovulation. * **Progesterone:** The "Thermogenic Hormone"—the rise in progesterone during the luteal phase causes a 0.5°F increase in Basal Body Temperature (BBT).

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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