Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 211: The ovulatory period corresponds to:

A. 14 days before menstruation (Correct Answer)
B. The day of menstruation
C. Increase in basal body temperature
D. 14 days after menstruation

Explanation: **Explanation:** The menstrual cycle is divided into two main phases: the **Follicular Phase** (variable in length) and the **Luteal Phase** (constant in length). **1. Why Option A is Correct:** The luteal phase, which occurs after ovulation, is remarkably constant at **14 days** across almost all women. This is because the lifespan of the *corpus luteum* is fixed; if fertilization does not occur, it undergoes involution (luteolysis) exactly 14 days after its formation. Therefore, regardless of whether a cycle is 28, 35, or 21 days long, ovulation always occurs approximately 14 days **before** the onset of the next menstrual period. **2. Why Other Options are Incorrect:** * **Option B:** Menstruation marks the beginning of the follicular phase (Day 1), not the ovulatory period. * **Option C:** While an increase in basal body temperature (BBT) occurs due to the thermogenic effect of **Progesterone**, this rise happens *after* ovulation has already occurred. It is a retrospective indicator of ovulation, not the ovulatory period itself. * **Option D:** This is only true in a perfect 28-day cycle. In cycles of different lengths, the follicular phase varies, making "14 days after menstruation" an unreliable predictor. **Clinical Pearls for NEET-PG:** * **LH Surge:** The most reliable predictor of impending ovulation (occurs 24–36 hours before). * **Mittelschmerz:** Pelvic pain experienced by some women mid-cycle during ovulation. * **Spinnbarkeit Phenomenon:** Under estrogen influence, cervical mucus becomes thin, watery, and stretchy (like egg white) just before ovulation. * **Fern Test:** Estrogen causes "ferning" of cervical mucus; Progesterone (post-ovulation) disappears this pattern.

Question 212: In a study it is observed that the right ovary ovulates more frequently than the left. What is the most likely exception among the following explanations for this phenomenon?

A. Anatomical asymmetry
B. Difference in blood supply to both ovaries
C. Right-handedness is more common in the population (Correct Answer)
D. Some embryological basis

Explanation: **Explanation:** In reproductive physiology, clinical studies have consistently observed that the **right ovary ovulates more frequently** (approximately 55-60% of the time) compared to the left. This phenomenon is attributed to physiological and anatomical asymmetries rather than behavioral traits. **Why Option C is the correct answer (The Exception):** Right-handedness is a neuromuscular and behavioral trait governed by cerebral dominance. There is **no physiological or neurological link** between handedness and the recruitment of primordial follicles or the dominance of an ovary. Therefore, it is the "exception" as it does not explain the observed frequency. **Analysis of other options:** * **Anatomical Asymmetry & Blood Supply (Options A & B):** The right and left ovarian veins have different drainage patterns. The right ovarian vein drains directly into the **Inferior Vena Cava (IVC)** at an acute angle, whereas the left ovarian vein drains into the **left renal vein** at a right angle. This results in higher hydrostatic pressure on the left side, potentially affecting follicular microcirculation and local hormone concentration. * **Embryological Basis (Option D):** During development, there are subtle differences in the migration of germ cells and the vascularization of the gonadal ridges. Some theories suggest the right ovary may contain a slightly higher density of primordial follicles from birth. **High-Yield Clinical Pearls for NEET-PG:** * **Ovulation Side & Pregnancy:** Oocytes from the right ovary have a statistically higher potential for pregnancy, likely due to the more favorable hemodynamic environment. * **Venous Drainage:** Remember the "Right to IVC, Left to Renal" rule—this is also why **Varicocele** is more common on the left side in males. * **Mittelschmerz:** Ovulatory pain can occur on either side, but if it occurs more frequently on the right, it must be differentiated from **acute appendicitis**.

Question 213: When does fertilization normally occur after ovulation?

A. Within 12-24 hours (Correct Answer)
B. Within 24-48 hours
C. Within 48-72 hours
D. Within 72-96 hours

Explanation: **Explanation:** The correct answer is **A. Within 12-24 hours.** **1. Why Option A is Correct:** Fertilization is highly time-sensitive due to the limited lifespan of the secondary oocyte. After ovulation, the ovum is picked up by the fimbriae and moves into the **ampulla of the fallopian tube** (the most common site of fertilization). The human ovum remains viable and capable of being fertilized for only **12 to 24 hours**. If fertilization does not occur within this window, the ovum begins to degenerate and is eventually phagocytized. **2. Why Other Options are Incorrect:** * **Options B, C, and D:** These timeframes exceed the biological viability of the unfertilized oocyte. While **spermatozoa** can survive in the female reproductive tract for approximately **48 to 72 hours** (waiting for the egg), the egg itself cannot wait that long. Therefore, for successful conception, coitus must occur close to the time of ovulation. **3. NEET-PG High-Yield Clinical Pearls:** * **Site of Fertilization:** The **Ampulla** of the fallopian tube is the specific site where fertilization occurs. * **Sperm Capacitation:** Before a sperm can fertilize an egg, it must undergo "capacitation" in the female reproductive tract, a process taking about **7 hours** to remove protective coatings from the acrosome. * **Zygote Transport:** Once fertilized, the zygote stays in the fallopian tube for about **3–4 days** before entering the uterine cavity. * **Implantation:** This typically occurs **6–7 days** after fertilization (around day 21 of a 28-day cycle), usually at the blastocyst stage. * **The "Window of Fertility":** Considering sperm longevity (3 days) and ovum viability (1 day), the fertile period is generally considered to be 3 days before to 1 day after ovulation.

Question 214: Cornification Index is maximum in which phase of the menstrual cycle?

A. Early secretory phase
B. Late proliferative phase (Correct Answer)
C. Late secretory phase
D. Early proliferative phase

Explanation: **Explanation:** The **Cornification Index (CI)** refers to the percentage of cornified (superficial) cells found in a vaginal smear. This index is a direct reflection of **estrogen** activity on the vaginal epithelium. Estrogen promotes the maturation of the vaginal mucosa, leading to the accumulation of superficial squamous cells characterized by pyknotic nuclei and acidophilic cytoplasm. 1. **Why Late Proliferative Phase is correct:** During the menstrual cycle, estrogen levels rise steadily throughout the proliferative phase, reaching their **peak just before ovulation** (the late proliferative phase). Consequently, the stimulation of the vaginal epithelium is maximal at this point, resulting in the highest Cornification Index (often >50-60%). 2. **Why other options are incorrect:** * **Early Proliferative Phase:** Estrogen levels are just beginning to rise; the smear is dominated by basal and parabasal cells, leading to a low CI. * **Early and Late Secretory Phases:** After ovulation, **progesterone** becomes the dominant hormone. Progesterone antagonizes the effects of estrogen on the vaginal mucosa, causing "shriveling" or folding of cells and an increase in intermediate cells (precornified cells). This leads to a significant decrease in the Cornification Index. **High-Yield Facts for NEET-PG:** * **Karyopyknotic Index (KI):** Also reaches its maximum during the **ovulatory/late proliferative phase** (measures cells with small, dense nuclei). * **Progesterone Effect:** Leads to the formation of **"Navicular cells"** (boat-shaped cells) and increased cellular clumping. * **Fern Test:** Also maximal in the late proliferative phase due to high estrogen and NaCl content in cervical mucus. * **Spinnbarkeit Phenomenon:** Maximum elasticity of cervical mucus occurs just before ovulation (Late Proliferative Phase).

Question 215: At which week of gestation does the placenta take over the function of the corpus luteum for hormone production?

A. 8 weeks (Correct Answer)
B. 12 weeks
C. 18 weeks
D. 24 weeks

Explanation: ### Explanation The transition of progesterone and estrogen production from the corpus luteum to the placenta is known as the **Luteal-Placental Shift**. **Why 8 weeks is correct:** During the first trimester, the corpus luteum (stimulated by hCG) is the primary source of progesterone, which is essential for maintaining the decidua and preventing menstruation. By the **7th to 9th week of gestation** (average 8 weeks), the syncytiotrophoblast of the placenta becomes sufficiently developed to synthesize enough steroid hormones to maintain the pregnancy independently. If the corpus luteum is removed before 7 weeks, miscarriage usually occurs; if removed after 9 weeks, the pregnancy typically continues due to placental compensation. **Why the other options are incorrect:** * **12 weeks:** While the placenta is fully "mature" in structure by the end of the first trimester, the functional shift for hormone production is already well-established by this point. * **18 & 24 weeks:** These are well into the second trimester. By this stage, the placenta is the massive endocrine powerhouse of the pregnancy, and the corpus luteum has long since regressed into the *corpus albicans of pregnancy*. **High-Yield NEET-PG Pearls:** * **hCG Peak:** Human Chorionic Gonadotropin peaks at **8–10 weeks**, coinciding with the time the placenta takes over hormone production. * **Progesterone Precursor:** Unlike the corpus luteum, the placenta cannot synthesize cholesterol de novo; it uses **maternal cholesterol** to produce progesterone. * **Estrogen Production:** The placenta lacks the enzyme *17α-hydroxylase*. Therefore, it relies on **DHEAS from the fetal adrenal glands** to produce Estriol ($E_3$), making $E_3$ a marker of feto-placental well-being.

Question 216: Which of the following hormones are involved in the initiation of lactation?

A. Oxytocin, Prolactin, and Human Placental Lactogen (HPL) (Correct Answer)
B. Oxytocin, Prolactin, and Thyroid hormone
C. Oxytocin, Human Placental Lactogen (HPL), and Thyroid hormone
D. Oxytocin, Prolactin, and Progesterone

Explanation: ### Explanation The initiation and maintenance of lactation (Lactogenesis) is a complex neuroendocrine process requiring the synergistic action of several hormones. **1. Why Option A is Correct:** * **Prolactin:** The primary hormone for milk production. During pregnancy, it promotes the development of mammary alveoli. Postpartum, the drop in estrogen and progesterone allows prolactin to initiate milk secretion. * **Oxytocin:** Responsible for the **"Milk Ejection Reflex"** (Let-down reflex). It causes contraction of the myoepithelial cells surrounding the alveoli, squeezing milk into the ducts. * **Human Placental Lactogen (HPL):** Also known as Human Chorionic Somatomammotropin (hCS). It mimics prolactin and growth hormone, preparing the breast tissue during pregnancy for future lactation. **2. Why Other Options are Incorrect:** * **Thyroid Hormone (Options B & C):** While thyroid hormones are permissive for overall metabolic health and can influence milk volume, they are not primary mediators for the *initiation* of lactation. * **Progesterone (Option D):** Progesterone is actually an **inhibitor** of lactation during pregnancy. It prevents prolactin from acting on the breast tissue. Lactation only begins once progesterone levels plummet following the delivery of the placenta. **3. NEET-PG High-Yield Pearls:** * **Mammogenesis:** Development of breasts (Estrogen for ducts; Progesterone for alveoli). * **Lactogenesis:** Initiation of milk secretion (Prolactin). * **Galactokinesis:** Milk ejection (Oxytocin). * **Galactopoiesis:** Maintenance of lactation (Prolactin and Suckling stimulus). * **Suckling Stimulus:** Inhibits **Dopamine** (Prolactin Inhibiting Factor) in the hypothalamus, leading to increased Prolactin levels.

Question 217: Infertility is a common feature in Sertoli cell-only syndrome because:

A. Too many Sertoli cells inhibit spermatogenesis
B. Proper blood-testis barrier is not established
C. There are no germ cells in this condition (Correct Answer)
D. Sufficient numbers of spermatozoa are not produced

Explanation: **Explanation:** **Sertoli cell-only syndrome (SCOS)**, also known as Del Castillo syndrome, is a condition characterized by the complete absence of germ cells in the seminiferous tubules. **1. Why Option C is Correct:** The fundamental pathology of SCOS is the **absence of the germinal epithelium**. While the seminiferous tubules are lined by functional Sertoli cells, the precursor cells (spermatogonia) that eventually undergo meiosis to become spermatozoa are missing. Without these germ cells, spermatogenesis cannot initiate, leading to absolute infertility and **non-obstructive azoospermia**. **2. Analysis of Incorrect Options:** * **Option A:** In SCOS, the number of Sertoli cells is not "too many"; rather, they are the *only* cells present. Infertility is due to the lack of germ cells, not an inhibitory effect of Sertoli cells. * **Option B:** While Sertoli cells form the blood-testis barrier, the primary cause of infertility in this specific syndrome is the lack of "raw material" (germ cells), not a structural failure of the barrier. * **Option D:** This is technically true but imprecise. "Sufficient numbers" implies some sperm are produced; in SCOS, there is a **total absence** of sperm production. **Clinical Pearls for NEET-PG:** * **Hormonal Profile:** Characterized by **elevated FSH** (due to decreased Inhibin B from dysfunctional/stressed Sertoli cells) but usually **normal LH and Testosterone** levels (as Leydig cells are typically unaffected). * **Diagnosis:** The definitive diagnosis is made via **Testicular Biopsy**, which shows "empty" tubules containing only Sertoli cells. * **Physical Exam:** Patients usually have normal secondary sexual characteristics but may have slightly smaller-than-average testes. * **Genetics:** Often associated with microdeletions in the **AZF (Azoospermia Factor) region** of the Y chromosome.

Question 218: What is the peak level of plasma progesterone in the luteal phase?

A. 5 ng/ml
B. 10 ng/ml
C. 15 ng/ml (Correct Answer)
D. 30 ng/ml

Explanation: **Explanation:** The menstrual cycle is divided into the follicular and luteal phases. Progesterone levels are minimal (<1 ng/ml) during the follicular phase. Following ovulation, the **corpus luteum** forms and begins secreting large amounts of progesterone to prepare the endometrium for potential implantation (secretory phase). **Why 15 ng/ml is correct:** Progesterone levels begin to rise immediately after ovulation, reaching their peak approximately **7 to 9 days after the LH surge** (mid-luteal phase). In a typical 28-day cycle, this occurs around day 21-23. Standard medical textbooks (like Ganong and Guyton) cite the peak plasma concentration of progesterone during this period as approximately **15 ng/ml (range 10–25 ng/ml)**. **Analysis of Incorrect Options:** * **A. 5 ng/ml:** This level is often used as a threshold to confirm that ovulation has occurred, but it does not represent the maximum peak reached during a healthy luteal phase. * **B. 10 ng/ml:** While 10 ng/ml is a healthy mid-luteal level, it is generally considered the lower end of the "peak" range rather than the average maximum value. * **D. 30 ng/ml:** This value is significantly higher than the average peak in a non-pregnant cycle. Such high levels are typically only seen during the first trimester of pregnancy. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** The corpus luteum is the primary source of progesterone in the luteal phase; the placenta takes over this role (luteal-placental shift) at approximately 7–9 weeks of gestation. * **Thermogenic Effect:** Progesterone acts on the hypothalamus to increase basal body temperature by **0.5°F to 1.0°F** after ovulation. * **Diagnostic Use:** A serum progesterone level >3 ng/ml on day 21 is a reliable indicator that ovulation has occurred.

Question 219: Blood levels of progesterone are highest during which phase of the ovarian cycle?

A. The follicular phase
B. The luteal phase (Correct Answer)
C. Ovulation
D. Menstruation

Explanation: **Explanation:** The ovarian cycle is divided into two main phases: the follicular phase and the luteal phase, separated by ovulation. **1. Why the Luteal Phase is Correct:** The luteal phase (Days 15–28) begins immediately after ovulation. Under the influence of Luteinizing Hormone (LH), the remnants of the ruptured Graafian follicle transform into a temporary endocrine gland called the **corpus luteum**. The primary function of the corpus luteum is the massive secretion of **progesterone** (and some estrogen) to prepare the endometrium for potential implantation. Progesterone levels peak approximately 7–8 days after ovulation (around Day 21–22 of a 28-day cycle). **2. Why the Other Options are Incorrect:** * **Follicular Phase:** This phase is dominated by **Estrogen**, secreted by developing follicles. Progesterone levels remain basal (very low) during this time. * **Ovulation:** This is a brief event triggered by the LH surge. While progesterone begins to rise slightly just before ovulation (due to luteinization of granulosa cells), it does not reach its peak until the corpus luteum is fully functional. * **Menstruation:** This occurs due to the **withdrawal** of progesterone and estrogen following the degeneration of the corpus luteum (into the corpus albicans). Therefore, progesterone levels are at their lowest during this phase. **High-Yield NEET-PG Pearls:** * **The "Gold Standard" for confirming ovulation:** Measuring serum progesterone levels during the mid-luteal phase (Day 21). A level >3 ng/mL typically indicates that ovulation has occurred. * **Thermogenic Effect:** Progesterone increases the Basal Body Temperature (BBT) by 0.5°F to 1.0°F after ovulation. * **Endometrial Change:** Progesterone is responsible for the **secretory changes** in the endometrium, whereas estrogen causes proliferative changes.

Question 220: What maintains the corpus luteum?

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

Explanation: **Explanation:** The corpus luteum (CL) is a temporary endocrine structure formed from the remnants of the ovarian follicle after ovulation. Its primary function is to secrete progesterone to support a potential pregnancy. **Why LH is the correct answer:** The maintenance and functional integrity of the corpus luteum during a normal menstrual cycle are strictly dependent on **Luteinizing Hormone (LH)**. LH provides the necessary "luteotropic" support by stimulating the luteal cells to produce progesterone. If fertilization does not occur, LH levels are insufficient to sustain the CL beyond 12–14 days, leading to its regression into the corpus albicans (luteolysis). **Analysis of Incorrect Options:** * **A. Progesterone:** This is a *product* of the corpus luteum, not the hormone that maintains it. It provides negative feedback to the hypothalamus and pituitary to inhibit further LH/FSH secretion. * **C. FSH:** While FSH is crucial for the growth and maturation of the Graafian follicle during the follicular phase, it does not play a primary role in maintaining the corpus luteum. * **D. Estrogen:** Like progesterone, estrogen is secreted by the corpus luteum (and the growing follicle), but it does not act as a trophic hormone for the CL's survival. **Clinical Pearls for NEET-PG:** * **Rescue of Corpus Luteum:** If pregnancy occurs, the role of LH is taken over by **human Chorionic Gonadotropin (hCG)**, which is an LH-analogue produced by the syncytiotrophoblast. hCG maintains the CL until the placenta takes over progesterone production (the luteal-placental shift) at approximately 7–9 weeks. * **Luteal Phase:** This phase is constant at 14 days because of the programmed lifespan of the corpus luteum in the absence of hCG. * **Hormone Profile:** The corpus luteum secretes high levels of **Progesterone** (predominant), Estrogen, and **Inhibin A**.

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

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