Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 111: What is the approximate daily sperm production in a healthy adult male?

A. 3 million per day
B. 12 million per day
C. 30 million per day
D. 120 million per day (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. 120 million per day.** **1. Why Option D is Correct:** In a healthy adult male, spermatogenesis is a continuous and highly productive process. The seminiferous tubules produce approximately **100 to 120 million sperm every 24 hours**. This high rate of production is essential to maintain the high sperm counts required for fertility, as millions of sperm are lost or destroyed within the female reproductive tract before reaching the oocyte. **2. Why Other Options are Incorrect:** * **Options A, B, and C:** These values (3, 12, and 30 million) are significantly lower than the physiological norm. A daily production rate in these ranges would eventually lead to **oligozoospermia** (low sperm count). For context, a total sperm count of less than 15 million per milliliter of ejaculate is clinically considered low. **3. High-Yield Facts for NEET-PG:** * **Duration of Spermatogenesis:** It takes approximately **64 to 74 days** for a spermatogonium to develop into a mature spermatozoon. * **Storage:** Mature sperm are stored primarily in the **epididymis**, where they undergo final maturation and gain motility. * **Hormonal Control:** Spermatogenesis is stimulated by **FSH** (acting on Sertoli cells) and **Testosterone** (produced by Leydig cells under the influence of **LH**). * **Sertoli Cells:** Often called "nurse cells," they provide structural and metabolic support to developing sperm and form the **blood-testis barrier**. * **Temperature:** Optimal spermatogenesis requires a temperature **2–3°C lower** than core body temperature, maintained by the pampiniform plexus and scrotal positioning.

Question 112: Which of the following is true about obstructive azoospermia?

A. FSH and LH are increased
B. Normal FSH and normal LH (Correct Answer)
C. LH is raised and FSH is normal
D. FSH is raised and LH is normal

Explanation: In reproductive physiology, azoospermia is classified into two main types: **Pre-testicular/Testicular (Non-obstructive)** and **Post-testicular (Obstructive)**. ### **Explanation of the Correct Answer** In **Obstructive Azoospermia**, the hypothalamic-pituitary-testicular axis is intact, and spermatogenesis (sperm production) within the testes is typically normal. The absence of sperm in the ejaculate is due to a physical blockage in the ductal system (e.g., vas deferens, epididymis). * Since the Sertoli cells are functioning normally, they produce **Inhibin B**, which keeps **FSH** levels within the normal range via negative feedback. * Since the Leydig cells are unaffected, testosterone production is normal, maintaining **LH** levels within the normal range. ### **Analysis of Incorrect Options** * **Option A, C, & D:** These patterns represent **Non-obstructive Azoospermia** (Primary Testicular Failure). When the testes fail to produce sperm or testosterone, the lack of negative feedback (low Inhibin B and low Testosterone) causes the pituitary to secrete compensatory high levels of FSH and LH. Specifically, an isolated **raised FSH** is the most sensitive marker of impaired spermatogenesis. ### **High-Yield Clinical Pearls for NEET-PG** * **Most common cause of Obstructive Azoospermia:** Congenital Bilateral Absence of Vas Deferens (CBAVD), often associated with **CFTR gene mutations** (Cystic Fibrosis). * **Diagnostic Marker:** In obstructive cases, the **testicular size** is usually normal, whereas in non-obstructive cases, the testes are often small and soft. * **Fructose Test:** If the obstruction is at the level of the ejaculatory ducts or there is seminal vesicle agenesis, the semen analysis will show **low volume, acidic pH, and absent fructose**.

Question 113: Which of the following parameters is NOT increased during pregnancy?

A. Vital capacity (Correct Answer)
B. Blood volume
C. Extracellular fluid
D. Weight

Explanation: **Explanation:** In pregnancy, significant physiological adaptations occur to meet the metabolic demands of the fetus. However, **Vital Capacity (VC)** remains **unchanged** or may show a negligible increase. While the growing uterus elevates the diaphragm by approximately 4 cm, there is a compensatory increase in the transverse and anteroposterior diameters of the thoracic cage due to the relaxation of ligamentous attachments (mediated by the hormone Relaxin). This ensures that the total volume of air that can be forcibly exhaled after a maximum inhalation remains stable. **Analysis of Options:** * **B. Blood Volume:** Increases significantly (up to 40–50%) to support placental perfusion. Plasma volume increases more than red cell mass, leading to "physiological anemia of pregnancy." * **C. Extracellular Fluid (ECF):** There is a marked increase in ECF due to sodium and water retention (mediated by the RAAS pathway and estrogen), contributing to the physiological edema often seen in the lower limbs. * **D. Weight:** An average weight gain of 11–12 kg is expected, attributed to the fetus, placenta, amniotic fluid, increased uterine/breast size, and expanded fluid volumes. **High-Yield NEET-PG Pearls:** * **Tidal Volume (TV):** Increases by ~40% (the most significant change in respiratory parameters). * **Functional Residual Capacity (FRC):** Decreases by ~20% due to the elevation of the diaphragm. * **Respiratory Rate:** Remains largely **unchanged**, but Minute Ventilation increases due to the rise in TV. * **State of Ventilation:** Pregnancy is a state of **chronic mild hyperventilation**, leading to respiratory alkalosis with renal compensation (decreased $PCO_2$).

Question 114: A young woman enters puberty with approximately 40,000 primary oocytes in her ovary. About how many of these primary oocytes will be ovulated over the entire reproductive life of the woman?

A. 40,000
B. 35,000
C. 480 (Correct Answer)
D. 48

Explanation: **Explanation:** The correct answer is **480 (Option C)**. This calculation is based on the duration of a woman's reproductive lifespan and the physiology of the menstrual cycle. **1. Why the Correct Answer is Right:** A woman’s reproductive life typically spans from **menarche** (onset of menstruation, ~12 years) to **menopause** (cessation of menstruation, ~52 years), lasting approximately **40 years**. * **Calculation:** 40 years × 12 months/year = **480 cycles**. * Since usually only one dominant follicle matures and releases an oocyte (ovulation) per cycle, roughly 400 to 500 oocytes are ovulated in a lifetime. The remaining 99.9% of the oocytes present at puberty undergo a degenerative process called **atresia**. **2. Why Incorrect Options are Wrong:** * **Options A & B (40,000 and 35,000):** These numbers represent the pool of available oocytes at puberty, not the number ovulated. Most oocytes are "wasted" through atresia regardless of whether a woman is pregnant, on oral contraceptives, or anovulatory. * **Option D (48):** This is mathematically too low, representing only about 4 years of reproductive life. **3. High-Yield NEET-PG Clinical Pearls:** * **Oocyte Count Timeline:** * **Peak:** 7 million at 20 weeks of gestation (fetal life). * **At Birth:** 1–2 million. * **At Puberty:** 300,000 to 400,000 (though the question uses 40,000 as a specific premise, the logic remains the same). * **Meiotic Arrest:** Primary oocytes are arrested in the **Prophase of Meiosis I (Dictyotene stage)** until ovulation. Secondary oocytes are arrested in **Metaphase of Meiosis II** until fertilization. * **Atresia:** This is an apoptotic process that is independent of FSH/LH levels during prepubertal years but becomes regulated by gonadotropins after puberty.

Question 115: Prolonged testosterone treatment to a man results in which of the following?

A. Increased spermatogenesis
B. Increased sperm motility
C. Azoospermia (Correct Answer)
D. Increased gonadotropins

Explanation: ### Explanation The correct answer is **C. Azoospermia**. #### 1. Mechanism of Action (The Hypothalamic-Pituitary-Gonadal Axis) The regulation of testicular function relies on a delicate negative feedback loop. When exogenous testosterone is administered over a prolonged period, it exerts **strong negative feedback** on the hypothalamus and the anterior pituitary. * **Hypothalamus:** Decreases the secretion of Gonadotropin-Releasing Hormone (GnRH). * **Anterior Pituitary:** Decreases the secretion of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). Spermatogenesis requires a very high local concentration of **intratesticular testosterone**, which is maintained by LH acting on Leydig cells. Exogenous testosterone suppresses LH, leading to a drastic drop in endogenous intratesticular testosterone levels. Additionally, the suppression of FSH removes the essential stimulus for Sertoli cells to support sperm production. Consequently, spermatogenesis ceases, leading to **azoospermia** (absence of sperm in the ejaculate). #### 2. Why Other Options are Incorrect * **A & B: Increased spermatogenesis/motility:** These are incorrect because exogenous testosterone paradoxically inhibits the natural production of sperm by suppressing the hormonal drive (FSH/LH) required for the germinal epithelium to function. * **D: Increased gonadotropins:** This is incorrect because testosterone inhibits the pituitary, leading to **decreased** levels of LH and FSH. #### 3. Clinical Pearls for NEET-PG * **"Male Contraceptive":** Testosterone is sometimes studied as a hormonal male contraceptive due to its ability to induce reversible azoospermia. * **Testicular Atrophy:** Prolonged use of anabolic steroids (testosterone analogues) leads to shrinking of the testes because the seminiferous tubules (which make up the bulk of testicular volume) become inactive. * **The Paradox:** While testosterone is necessary for libido and secondary sexual characteristics, **exogenous** testosterone is a potent inhibitor of fertility.

Question 116: In evaluating the menstrual cycle, which statement is true?

A. Estrogen secretion predominates during the week prior to menstruation.
B. Ovulation follows a surge in LH. (Correct Answer)
C. Progesterone predominates the first week after menstruation.
D. FSH is released at midcycle.

Explanation: ### Explanation **Correct Answer: B. Ovulation follows a surge in LH.** The menstrual cycle is governed by the complex interplay of the hypothalamic-pituitary-ovarian axis. The **Luteinizing Hormone (LH) surge** is the critical trigger for ovulation. This surge is initiated by a sustained rise in estrogen (positive feedback) from the dominant follicle. Ovulation typically occurs **10–12 hours after the LH peak** and approximately **32–36 hours after the initial rise** in LH levels. The surge induces the primary oocyte to complete Meiosis I and triggers the rupture of the Graafian follicle. **Analysis of Incorrect Options:** * **Option A:** The week prior to menstruation is the **late luteal phase**. During this time, the corpus luteum begins to degenerate, leading to a **decline** in both estrogen and progesterone levels, not a predominance of estrogen. * **Option C:** The first week after menstruation corresponds to the **early follicular phase**. During this stage, **Estrogen** is the rising hormone as follicles develop. Progesterone only predominates during the **luteal phase** (post-ovulation), secreted by the corpus luteum. * **Option D:** While a small FSH peak occurs at midcycle (concomitant with the LH surge), the statement is less specific than Option B. FSH's primary role is the recruitment of follicles at the *beginning* of the cycle. **High-Yield NEET-PG Pearls:** * **The "Trigger":** Estrogen exerts negative feedback on the pituitary at low levels but switches to **positive feedback** once levels exceed 200 pg/mL for ~48 hours, triggering the LH surge. * **Mittelschmerz Sign:** Pelvic pain associated with ovulation due to follicular fluid or blood irritating the peritoneum. * **Luteal Phase Constancy:** While the follicular phase varies in length, the luteal phase is almost always constant at **14 days**. * **Basal Body Temperature (BBT):** Progesterone (thermogenic) causes a 0.5–1.0°F rise in BBT after ovulation.

Question 117: Spermatogenesis occurs at what temperature relative to core body temperature?

A. Core body temperature
B. A temperature lower than core body temperature (Correct Answer)
C. A temperature higher than core body temperature
D. Temperature does not play a role in spermatogenesis

Explanation: **Explanation:** **1. Why Option B is Correct:** Spermatogenesis is a highly temperature-sensitive process. For optimal sperm production and maturation, the testes must be maintained at a temperature approximately **2°C to 3°C lower than the core body temperature** (around 34°C–35°C). This lower temperature is essential for the enzymatic activities involved in DNA synthesis and meiosis within the seminiferous tubules. High temperatures lead to apoptosis of germ cells and decreased sperm motility. **2. Why Other Options are Incorrect:** * **Option A & C:** Exposure to core body temperature (37°C) or higher inhibits the maturation of spermatogonia. Prolonged exposure to heat (e.g., high fevers, tight clothing, or hot baths) can lead to oligospermia (low sperm count). * **Option D:** Temperature is one of the most critical regulatory factors for male fertility. The body utilizes specialized thermoregulatory mechanisms to ensure this gradient is maintained. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Thermoregulatory Mechanisms:** The body maintains this temperature gradient via: * **The Scrotum:** Acts as a "radiator" due to its thin skin and lack of subcutaneous fat. * **Cremaster and Dartos Muscles:** Contract to pull testes closer to the body in cold and relax to move them away in heat. * **Pampiniform Plexus:** A network of veins that acts as a **counter-current heat exchanger**, cooling the arterial blood before it reaches the testes. * **Cryptorchidism:** Failure of the testes to descend into the scrotum. If not corrected surgically (Orchidopexy) by age 1, the exposure to core body temperature leads to permanent damage of the seminiferous tubules and an increased risk of testicular cancer. * **Varicocele:** Dilation of the pampiniform plexus (usually on the left side) which impairs heat exchange, raising testicular temperature and causing infertility.

Question 118: Polar bodies are formed during which process?

A. Spermatogenesis
B. Organogenesis
C. Oogenesis (Correct Answer)
D. Morphogenesis

Explanation: **Explanation:** **Correct Answer: C. Oogenesis** Polar bodies are a hallmark of **oogenesis**, the process of female gamete formation. Unlike spermatogenesis, which produces four equal-sized functional sperm, oogenesis involves **unequal cytoplasmic division**. * During Meiosis I, the primary oocyte divides to form a large **secondary oocyte** and a small **first polar body**. * During Meiosis II (triggered by fertilization), the secondary oocyte divides into a large **ovum** and a **second polar body**. The purpose of polar bodies is to discard extra sets of chromosomes while conserving the maximum amount of cytoplasm and organelles for the potential zygote. **Why other options are incorrect:** * **A. Spermatogenesis:** This process involves equal cytoplasmic division, resulting in four functional, haploid spermatozoa from one primary spermatocyte. No polar bodies are formed. * **B. Organogenesis:** This refers to the phase of embryonic development where germ layers (ectoderm, mesoderm, endoderm) differentiate into specific organs. * **D. Morphogenesis:** This is the biological process that causes an organism to develop its shape, involving cell growth and differentiation. **High-Yield NEET-PG Pearls:** * **Meiotic Arrests:** Oogenesis is discontinuous. It arrests in **Prophase I (Diplotene stage)** at birth and remains so until puberty. It arrests again in **Metaphase II** during ovulation, completing only if fertilization occurs. * **First Polar Body:** Usually degenerates, but its presence in the perivitelline space is a key marker of **oocyte maturity** (MII stage) in IVF procedures. * **Chromosome Count:** Both the secondary oocyte and the first polar body are haploid (23, X).

Question 119: In which of the following transitions does meiosis occur?

A. Primary to secondary spermatocyte (Correct Answer)
B. Secondary spermatocyte to globular spermatid
C. Germ cells to spermatogonium
D. Spermatogonium to primary spermatocyte

Explanation: **Explanation:** The process of spermatogenesis involves a series of cell divisions and transformations. The correct answer is **A (Primary to secondary spermatocyte)** because this transition marks the initiation of **Meiosis I (Reduction Division).** 1. **Why Option A is Correct:** Primary spermatocytes are diploid cells ($2n$, $46$ chromosomes). They undergo **Meiosis I** to produce two secondary spermatocytes. This is the critical step where the chromosome number is halved ($n$, $23$ chromosomes), making secondary spermatocytes haploid. 2. **Why Other Options are Incorrect:** * **Option B:** The transition from secondary spermatocyte to spermatid is **Meiosis II (Equational Division).** While technically part of the meiotic process, the primary-to-secondary transition is the hallmark "first" meiotic division. * **Option C:** Germ cells (gonocytes) differentiate into spermatogonia via **mitosis** during fetal development and early puberty. * **Option D:** Spermatogonia (Type B) differentiate into primary spermatocytes through **mitosis and growth**, not meiosis. At this stage, the cell remains diploid ($2n$). **High-Yield NEET-PG Pearls:** * **Spermiogenesis:** This is the transformation of a globular spermatid into a mature, motile spermatozoon (no cell division occurs here). * **Duration:** The entire process of spermatogenesis takes approximately **74 days**. * **Blood-Testis Barrier:** Formed by **Sertoli cells**, this barrier protects the developing haploid cells (secondary spermatocytes onwards) from the immune system, as they are genetically distinct from the host. * **Hormonal Control:** LH stimulates Leydig cells (testosterone), while FSH stimulates Sertoli cells to support spermatogenesis.

Question 120: Which structure contributes the largest volume to semen?

A. Seminal vesicle (Correct Answer)
B. Cowper's glands
C. Prostate gland
D. Urethral glands

Explanation: **Explanation:** The correct answer is **A. Seminal vesicle**. The composition of semen is a high-yield topic in reproductive physiology. Semen is a mixture of spermatozoa and secretions from various accessory sex glands. The **seminal vesicles** contribute approximately **60–70%** of the total ejaculate volume. Their secretion is alkaline, thick, and rich in **fructose** (the primary energy source for sperm motility), prostaglandins, and clotting proteins (seminogelin). **Analysis of Incorrect Options:** * **B. Cowper's glands (Bulbourethral glands):** These contribute less than **5%** of the volume. They secrete a clear, mucoid pre-ejaculate that lubricates the urethra and neutralizes residual acidic urine. * **C. Prostate gland:** This is the second-largest contributor, accounting for about **20–30%** of the volume. Prostatic fluid is thin, milky, and contains citrate, calcium, and **Prostate-Specific Antigen (PSA)**, which helps in the liquefaction of the coagulum. * **D. Urethral glands (Glands of Littre):** These provide a negligible volume, primarily secreting mucus to protect the urethral epithelium. **High-Yield NEET-PG Pearls:** 1. **Fructose Test:** Since fructose is produced exclusively by the seminal vesicles, its absence in semen (azoospermia with absent fructose) indicates **seminal vesicle obstruction** or congenital bilateral absence of the vas deferens (CBAVD). 2. **pH Balance:** Seminal vesicle fluid is alkaline, which helps neutralize the acidic environment of the male urethra and the female vagina. 3. **Coagulation & Liquefaction:** Seminal vesicles cause semen to clot (to keep it near the cervix), while the prostate gland (via PSA) later liquefies the clot to release the sperm.

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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