Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 231: What is the approximate duration required for the production of mature spermatozoa from spermatogonia?

A. 32 days
B. 70 days (Correct Answer)
C. 150 days
D. Unaffected by Kallmann's syndrome

Explanation: **Explanation:** The process of **spermatogenesis**—the transformation of primitive germ cells (spermatogonia) into mature spermatozoa—is a highly regulated and time-consuming process. In humans, the total duration of this cycle is approximately **74 days** (commonly rounded to **70 days** in standard textbooks like Guyton and Ganong). 1. **Why Option B is Correct:** Spermatogenesis occurs in the seminiferous tubules and involves three main phases: * **Spermatocytogenesis (Mitosis):** Spermatogonia divide to produce primary spermatocytes. * **Meiosis:** Primary spermatocytes undergo two divisions to become haploid spermatids. * **Spermiogenesis:** The morphological transformation of spherical spermatids into elongated, motile spermatozoa. The entire sequence takes roughly 70–74 days. Note that an additional 10–14 days are required for these sperm to mature and gain motility within the **epididymis**. 2. **Why Other Options are Incorrect:** * **Option A (32 days):** This is too short; it represents only a portion of the spermatogenic cycle. * **Option C (150 days):** This is excessively long. While sperm can be stored in the vas deferens for several weeks, the production cycle does not exceed 75 days. * **Option D:** This is factually incorrect. **Kallmann’s Syndrome** (hypogonadotropic hypogonadism) involves a deficiency of GnRH, leading to low FSH and LH. Since FSH and Testosterone are essential for spermatogenesis, this condition directly causes infertility. **High-Yield Clinical Pearls for NEET-PG:** * **Spermiogenesis vs. Spermiation:** Spermiogenesis is the *transformation* of spermatids to sperm; Spermiation is the *release* of mature sperm from Sertoli cells into the tubule lumen. * **Temperature Sensitivity:** Spermatogenesis requires a temperature **2–3°C lower** than core body temperature. This is why cryptorchidism leads to infertility. * **Blood-Testis Barrier:** Formed by **tight junctions between Sertoli cells**, it protects developing germ cells from the immune system.

Question 232: Which of the following is not a phase of the endometrium?

A. Progestational phase
B. Menstrual phase
C. Ovulatory phase (Correct Answer)
D. Proliferative phase

Explanation: The endometrial cycle refers specifically to the histological changes occurring in the **uterine lining** in response to ovarian hormones. While the ovary undergoes an "ovulatory phase," the endometrium does not. ### Why "Ovulatory Phase" is the Correct Answer Ovulation is an **ovarian event**, not an endometrial one. It refers to the release of the secondary oocyte from the Graafian follicle triggered by the LH surge. During this brief transition, the endometrium is simply finishing its proliferative stage and beginning its secretory transformation; there is no distinct histological "ovulatory phase" of the uterine lining. ### Explanation of Other Phases * **Proliferative Phase (Option D):** Occurs under the influence of **estrogen**. It involves the growth of endometrial glands and stromal vessels. It corresponds to the follicular phase of the ovary. * **Progestational Phase (Option A):** Also known as the **Secretory Phase**. It occurs after ovulation under the influence of **progesterone** from the corpus luteum. Glands become tortuous and begin secreting glycogen-rich fluid to prepare for implantation. * **Menstrual Phase (Option B):** Triggered by the withdrawal of progesterone and estrogen (involution of the corpus luteum), leading to the shedding of the *stratum functionale*. ### NEET-PG High-Yield Pearls * **Dating the Endometrium:** The most reliable histological sign of recent ovulation is **subnuclear vacuolation** in the endometrial glands (early secretory phase). * **Master Regulator:** Estrogen drives proliferation (mitosis), while Progesterone drives secretion and limits proliferation. * **Duration:** The secretory phase is constant at **14 days**, whereas the proliferative phase varies in length, determining the overall cycle duration.

Question 233: Which of the following is normally present in the urine of a pregnant woman in her 3rd trimester?

A. Glucose (Correct Answer)
B. Fructose
C. Galactose
D. Lactose

Explanation: **Explanation:** The correct answer is **Glucose**. **1. Why Glucose is Correct:** During pregnancy, particularly in the 2nd and 3rd trimesters, there is a significant increase in the **Glomerular Filtration Rate (GFR)**—often by as much as 50%. This results in a higher load of glucose being filtered into the renal tubules. Simultaneously, there is a physiological **decrease in the renal threshold for glucose** (the maximum reabsorptive capacity of the proximal convoluted tubule, or $T_mG$). Because the tubules cannot keep up with the increased filtered load, "physiological glucosuria" occurs in approximately 50-70% of healthy pregnant women, even in the absence of diabetes mellitus. **2. Why the Other Options are Incorrect:** * **Fructose:** Fructosuria is not a physiological feature of pregnancy; its presence usually indicates a rare metabolic disorder (e.g., Essential Fructosuria). * **Galactose:** While trace amounts may appear in rare instances, it is not a normal or expected finding in the 3rd trimester. * **Lactose:** While **Lactosuria** can occur in late pregnancy and during lactation (due to mammary gland activity), **Glucose** is the most common and physiologically expected finding due to the systemic changes in renal hemodynamics. In the context of standard medical examinations, glucose is the primary sugar associated with altered renal thresholds in pregnancy. **3. Clinical Pearls for NEET-PG:** * **GFR in Pregnancy:** Increases due to increased cardiac output and renal plasma flow. * **Glucosuria vs. Gestational Diabetes:** While physiological glucosuria is common, any positive dipstick for glucose in pregnancy warrants further screening (like an OGTT) to rule out Gestational Diabetes Mellitus (GDM). * **Proteinuria:** Unlike glucose, significant proteinuria ($>300$ mg/day) is **never** normal and suggests pre-eclampsia.

Question 234: Time of ovulation is detected by all EXCEPT:

A. Urine LH
B. Urine FSH (Correct Answer)
C. Serum progesterone
D. Basal body temperature

Explanation: **Explanation:** The detection of ovulation is crucial for fertility monitoring. The correct answer is **Urine FSH** because, while FSH levels do rise slightly during the mid-cycle surge, they are not used clinically to predict or confirm the exact timing of ovulation. **Why the other options are used to detect ovulation:** * **Urine LH (Option A):** This is the "Gold Standard" for home prediction. The LH surge occurs approximately 24–36 hours before ovulation. Detecting the LH peak in urine is the most reliable way to identify the upcoming fertile window. * **Serum Progesterone (Option C):** Progesterone is secreted by the Corpus Luteum *after* ovulation. A mid-luteal phase serum progesterone level (measured on Day 21 of a 28-day cycle) >3 ng/mL is a definitive retrospective indicator that ovulation has occurred. * **Basal Body Temperature (Option D):** Under the influence of thermogenic progesterone, the BBT rises by 0.5–1.0°F after ovulation. While it cannot predict ovulation, it is a useful tool to confirm that ovulation has taken place. **High-Yield NEET-PG Pearls:** 1. **Spinnbarkeit Phenomenon:** Just before ovulation, cervical mucus becomes thin, watery, and stretchy (resembling egg white) due to high estrogen. 2. **Fern Test:** Estrogen causes "ferning" patterns in cervical mucus; this disappears after ovulation due to progesterone. 3. **Mittelschmerz:** Pelvic pain experienced by some women mid-cycle at the time of follicular rupture. 4. **Ultrasonography:** Serial TVS (Transvaginal Sonography) showing the disappearance of a dominant follicle is the most accurate way to confirm ovulation.

Question 235: The umbilical venous pO2 is what?

A. 20-25 mmHg
B. 25-48 mmHg
C. 30-32 mmHg (Correct Answer)
D. 40-45 mmHg

Explanation: ### Explanation The correct answer is **30-32 mmHg**. **Underlying Concept:** In fetal circulation, the **umbilical vein** is unique because it carries oxygenated blood from the placenta to the fetus. Despite being "oxygenated," the fetal $pO_2$ is significantly lower than adult arterial levels (approx. 95-100 mmHg). This is due to the high metabolic demand of the placenta and the diffusion gradient required for oxygen transfer. The umbilical venous $pO_2$ typically ranges between **30-35 mmHg**, with a saturation of approximately 70-80%. The fetus compensates for this "relative hypoxia" by having a higher concentration of **Fetal Hemoglobin (HbF)**, which has a higher affinity for oxygen. **Analysis of Options:** * **A (20-25 mmHg):** This value is too low for the umbilical vein; it more closely resembles the $pO_2$ of the **umbilical arteries** (approx. 15-25 mmHg), which carry deoxygenated blood back to the placenta. * **B (25-48 mmHg):** While 30 mmHg falls within this range, the upper limit (48 mmHg) is physiologically inaccurate for fetal venous blood. * **D (40-45 mmHg):** This range is too high. By the time blood reaches the fetal heart and is pumped to the upper body, the $pO_2$ has already dropped due to mixing in the IVC (via ductus venosus). **High-Yield Clinical Pearls for NEET-PG:** * **Highest $pO_2$ in Fetus:** The **Umbilical Vein** (30-32 mmHg). * **Lowest $pO_2$ in Fetus:** The **Umbilical Arteries** (15-25 mmHg). * **HbF Shift:** The oxygen-dissociation curve for HbF is shifted to the **left** compared to adult HbA, allowing the fetus to bind oxygen more effectively at lower partial pressures. * **Double Haldane Effect:** This facilitates $CO_2$ transfer from the fetus to the mother, while the **Double Bohr Effect** facilitates $O_2$ transfer from the mother to the fetus.

Question 236: Which of the following is NOT a normal phase in the physiology of normal sexual arousal and orgasm?

A. Erogenous Phase (Correct Answer)
B. Plateau Phase
C. Orgasm
D. Refractory Period

Explanation: The human sexual response cycle is a physiological model describing the changes that occur during sexual activity. The most widely accepted model was proposed by **Masters and Johnson**, which consists of four distinct, sequential phases. ### **Explanation of the Correct Answer** **A. Erogenous Phase:** This is the correct answer because it is **not** a recognized phase in the Masters and Johnson model. While "erogenous zones" refer to areas of the body sensitive to sexual stimulation, there is no physiological "Erogenous Phase." The four actual phases are Excitement, Plateau, Orgasm, and Resolution. ### **Explanation of Incorrect Options** * **B. Plateau Phase:** This is a valid phase characterized by a leveling off of sexual tension. In this stage, heart rate, respiration, and muscle tension increase further, and the "orgasmic platform" (engorgement of the outer third of the vagina) develops in females. * **C. Orgasm:** This is the shortest phase, marked by involuntary muscular contractions and the release of sexual tension. In males, it typically involves ejaculation; in females, it involves rhythmic contractions of the uterus and vaginal walls. * **D. Refractory Period:** This is a sub-phase of the **Resolution Phase** occurring primarily in males. During this time, further stimulation cannot trigger another orgasm. This period typically lengthens with age. ### **High-Yield Clinical Pearls for NEET-PG** * **Masters and Johnson Model:** Excitement → Plateau → Orgasm → Resolution (Mnemonic: **EPOR**). * **Kaplan’s Model:** An alternative model that includes **Desire**, Excitement, and Orgasm. * **Autonomic Control:** * **Erection** (Excitement) is mediated by the **Parasympathetic** nervous system ("Point"). * **Ejaculation** (Orgasm) is mediated by the **Sympathetic** nervous system ("Shoot"). * **Refractory Period:** Females generally do not have a physiological refractory period and are capable of multiple orgasms, unlike males.

Question 237: What is the size of a resting follicle?

A. 0.2 mm
B. 0.02 mm (Correct Answer)
C. 2 mm
D. 20 mm

Explanation: **Explanation:** The correct answer is **0.02 mm (20 µm)**. **1. Understanding the Concept:** A "resting follicle" refers to a **primordial follicle**. This is the most immature stage of follicular development, consisting of a primary oocyte arrested in the prophase of Meiosis I, surrounded by a single layer of flattened (squamous) granulosa cells. At this stage, the follicle is microscopic, measuring approximately **0.02 mm to 0.03 mm** in diameter. These follicles constitute the ovarian reserve and can remain in this "resting" state for decades. **2. Analysis of Incorrect Options:** * **A. 0.2 mm:** This size corresponds to a **primary or early secondary (pre-antral) follicle**. As the primordial follicle is recruited, the granulosa cells become cuboidal and proliferate, increasing the diameter. * **C. 2 mm:** This is the approximate size of an **early antral follicle**. At this stage, a fluid-filled cavity (antrum) begins to form. Follicles of this size are visible on high-resolution ultrasound. * **D. 20 mm:** This represents a **mature Graafian follicle** (pre-ovulatory follicle). A follicle typically reaches 18–24 mm just before ovulation occurs. **3. High-Yield NEET-PG Pearls:** * **Oocyte size:** The oocyte itself within a primordial follicle is about 15–20 µm. * **Recruitment:** The transition from a resting (primordial) follicle to a primary follicle is **gonadotropin-independent**. * **Dominant Follicle:** Selection of the dominant follicle occurs during the mid-follicular phase (days 5–7) when it reaches about 5–10 mm. * **Growth Rate:** Once dominant, the follicle grows at a rate of approximately **2 mm/day** until it reaches maturity (approx. 20 mm).

Question 238: Which of the following is not related to the menstrual cycle?

A. Hormonal changes
B. Vaginal cytology (Correct Answer)
C. Estradiol changes
D. Endometrial sampling

Explanation: The menstrual cycle is a complex physiological process characterized by rhythmic changes in the female reproductive system, primarily driven by the hypothalamic-pituitary-ovarian axis. ### **Explanation of the Correct Answer** **Option B (Vaginal Cytology)** is the correct answer because it is **not a standard or reliable method** used to monitor or define the phases of the menstrual cycle in clinical practice. While the vaginal epithelium does undergo subtle changes due to estrogen (maturation of squamous cells), these changes are non-specific and can be influenced by infections, local inflammation, or trauma. Historically, the "Maturation Index" was used, but it has been entirely superseded by hormonal assays and ultrasound. ### **Analysis of Incorrect Options** * **A & C (Hormonal and Estradiol changes):** These are the core drivers of the cycle. The fluctuations in GnRH, FSH, LH, Estradiol, and Progesterone define the follicular and luteal phases. Estradiol specifically peaks just before ovulation to trigger the LH surge. * **D (Endometrial sampling):** The endometrium is the primary "target organ" of the menstrual cycle. Histological examination (dating of the endometrium) via biopsy is a classic method to confirm ovulation and assess the secretory changes induced by progesterone. ### **High-Yield NEET-PG Pearls** * **Gold Standard for Ovulation:** The most accurate way to confirm ovulation is a **Transvaginal Ultrasound (TVUS)** showing follicular collapse or a **Mid-luteal Progesterone** level (measured on Day 21). * **Fern Test:** High estrogen levels (pre-ovulatory) cause cervical mucus to form a "fern" pattern. Progesterone (post-ovulatory) disappears this pattern. * **Spinnbarkeit Phenomenon:** Refers to the elasticity of cervical mucus under the influence of peak estrogen levels just before ovulation. * **Basal Body Temperature (BBT):** Progesterone has a **thermogenic effect**, causing a rise of 0.5–1.0°F after ovulation.

Question 239: Ovaries secrete all of the following hormones except?

A. Androstenedione
B. 17-α-Hydroxyprogesterone
C. Dehydroepiandrosterone
D. Dihydrotestosterone (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Dihydrotestosterone (DHT)**. **1. Why Dihydrotestosterone is the correct answer:** The ovary is capable of synthesizing various steroid hormones from cholesterol via the Δ5 and Δ4 pathways. However, **Dihydrotestosterone (DHT)** is not a primary secretory product of the ovary. DHT is a potent androgen formed primarily in **peripheral tissues** (such as the skin and hair follicles) through the action of the enzyme **5-α-reductase** on testosterone. While the ovary produces testosterone, it lacks significant 5-α-reductase activity to secrete DHT directly into the circulation. **2. Analysis of incorrect options:** * **A. Androstenedione:** This is the primary androgen secreted by the **Theca cells** of the ovary. It serves as the immediate precursor for estrone and testosterone. * **B. 17-α-Hydroxyprogesterone:** This is an intermediate in the steroidogenic pathway (produced from progesterone or 17-α-hydroxypregnenolone) and is secreted by the ovary, particularly during the luteal phase. * **C. Dehydroepiandrosterone (DHEA):** The ovary secretes small amounts of DHEA (about 20% of circulating DHEA), though the majority originates from the adrenal cortex. **3. NEET-PG High-Yield Pearls:** * **Two-Cell, Two-Gonadotropin Theory:** LH stimulates **Theca cells** to produce androgens (Androstenedione/Testosterone); FSH stimulates **Granulosa cells** to convert these androgens into estrogens via the enzyme **Aromatase**. * **Potency:** DHT is the most potent natural androgen, followed by Testosterone, then Androstenedione. * **Clinical Correlation:** In Polycystic Ovary Syndrome (PCOS), there is an elevation in ovarian androstenedione and testosterone, but the hirsutism is often driven by the peripheral conversion of these precursors to **DHT** in the skin.

Question 240: Which is the shortest stage in the human sexual response cycle?

A. Excitement
B. Resolution
C. Orgasm (Correct Answer)
D. Desire phase

Explanation: **Explanation:** The human sexual response cycle, as described by Masters and Johnson, consists of four distinct phases: Excitement, Plateau, Orgasm, and Resolution. **Why Orgasm is the correct answer:** The **Orgasm phase** is the shortest stage of the cycle, typically lasting only **3 to 15 seconds**. Physiologically, it is characterized by involuntary rhythmic muscular contractions of the pelvic floor (bulbocavernosus muscle), the uterus/vagina in females, and the prostate/seminal vesicles in males. It represents the peak of physical pleasure and the discharge of accumulated neuromuscular tension. **Analysis of Incorrect Options:** * **Excitement:** This is the initial phase triggered by physical or psychological stimuli. It can last from several minutes to several hours, making it significantly longer than the orgasmic phase. * **Resolution:** This is the final phase where the body returns to its normal physiological state. In males, this includes a "refractory period." This process generally takes 10 to 30 minutes, but can last longer. * **Desire Phase:** This was added later by Helen Singer Kaplan (the Triphasic Model). It represents the psychological urge or drive for sexual activity and has no fixed duration, often lasting much longer than the physiological act itself. **High-Yield NEET-PG Pearls:** * **Masters and Johnson Model:** Excitement → Plateau → Orgasm → Resolution (EPOR). * **Kaplan’s Model:** Desire → Excitement → Orgasm. * **Neurological Control:** The **Excitement** phase (erection) is primarily **Parasympathetic** (S2-S4), while **Orgasm/Emission** is primarily **Sympathetic** (T11-L2). Remember: "Point (Parasympathetic) and Shoot (Sympathetic)." * **Refractory Period:** This occurs only in males during the Resolution phase, during which further orgasm is physiologically impossible. Females do not have a definitive refractory period and are capable of multiple orgasms.

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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