Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 71: What is the average reproductive lifespan of an ovum?

A. 6-12 hours
B. 12-24 hours (Correct Answer)
C. 24-36 hours
D. 3 days

Explanation: **Explanation:** The reproductive lifespan of an ovum (secondary oocyte) refers to the duration it remains viable and capable of being fertilized after ovulation. **1. Why Option B is Correct:** Once the ovum is released from the Graafian follicle into the fallopian tube, it remains viable for a very short window, typically **12 to 24 hours**. If fertilization by a sperm does not occur within this timeframe, the ovum undergoes involution and degenerates. This narrow window is a critical factor in determining the "fertile period" of the menstrual cycle. **2. Why Other Options are Incorrect:** * **Option A (6-12 hours):** This is too short. While the ovum is at its peak fertility immediately after ovulation, it generally maintains viability for at least 12 hours. * **Option C (24-36 hours):** This exceeds the typical physiological lifespan of the ovum. While some studies suggest rare instances of longer survival, the standard medical consensus for exams is 24 hours. * **Option D (3 days):** This is incorrect for the ovum but is the approximate **lifespan of a spermatozoon** within the female reproductive tract (which can survive 48–72 hours). **3. High-Yield Clinical Pearls for NEET-PG:** * **Sperm Viability:** Sperm can survive in the female tract for **2–3 days**, whereas the ovum survives for only **12–24 hours**. Therefore, for fertilization to occur, intercourse must happen within the window of 48 hours before to 24 hours after ovulation. * **Site of Fertilization:** Fertilization typically occurs in the **Ampulla** of the fallopian tube. * **Meiotic State:** At the time of ovulation, the egg is a **secondary oocyte** arrested in **Metaphase of Meiosis II**. Meiosis II is only completed if fertilization occurs.

Question 72: A 17-year-old primigravida asks what to expect during her pregnancy. What normally occurs during pregnancy?

A. Blood volume increases (Correct Answer)
B. Hematocrit increases
C. Tidal volume decreases
D. Functional residual capacity increases

Explanation: During pregnancy, the maternal body undergoes significant physiological adaptations to meet the metabolic demands of the fetus and protect the mother against blood loss during delivery. **Correct Option: A. Blood volume increases** Total blood volume increases significantly (by 40–50%) starting in the first trimester. This is driven by an increase in both plasma volume and red cell mass. The increase in plasma volume is mediated by the activation of the Renin-Angiotensin-Aldosterone System (RAAS), leading to sodium and water retention. **Explanation of Incorrect Options:** * **B. Hematocrit increases:** While red cell mass increases, the increase in **plasma volume is disproportionately greater**. This results in hemodilution, leading to a physiological decrease in hematocrit and hemoglobin concentration (Physiological Anemia of Pregnancy). * **C. Tidal volume decreases:** Progesterone acts as a direct respiratory stimulant. Consequently, **Tidal Volume (TV) increases** by approximately 40%, leading to increased minute ventilation and a state of physiological respiratory alkalosis. * **D. Functional residual capacity increases:** As the uterus enlarges, it pushes the diaphragm upward by about 4 cm. This reduces the resting volume of the lungs, leading to a **decrease in Functional Residual Capacity (FRC)** and Expiratory Reserve Volume (ERV). **High-Yield NEET-PG Pearls:** * **Cardiac Output:** Increases by 30–50%, peaking at 20–24 weeks. Stroke volume increases early, while Heart Rate increases later in pregnancy. * **Coagulation:** Pregnancy is a **hypercoagulable state** (increased Factors VII, VIII, IX, X, and Fibrinogen; decreased Protein S). * **BP:** Systemic Vascular Resistance (SVR) decreases due to progesterone, leading to a **nadir in blood pressure** during the second trimester.

Question 73: All of the following are placental hormones, EXCEPT:

A. Chorionic gonadotropin
B. Chorionic thyrotropin
C. Chorionic corticotropin
D. Chorionic calcitonin (Correct Answer)

Explanation: The placenta acts as a sophisticated endocrine organ, producing hormones that mimic the functions of the hypothalamus and the anterior pituitary to maintain pregnancy and fetal development. ### **Explanation of the Correct Answer** **Option D (Chorionic calcitonin)** is the correct answer because it is **not** a placental hormone. Calcitonin is primarily secreted by the parafollicular (C-cells) of the thyroid gland. While the placenta produces various "chorionic" versions of pituitary hormones, it does not produce a specific chorionic version of calcitonin. Calcium homeostasis in the fetus is primarily regulated by fetal parathyroid hormone (PTH) and PTH-related protein (PTHrP). ### **Analysis of Incorrect Options** * **A. Chorionic gonadotropin (hCG):** Produced by the syncytiotrophoblast, it is the first hormone secreted by the placenta. Its primary role is to rescue the corpus luteum to ensure continued progesterone production. * **B. Chorionic thyrotropin (hCT):** The placenta produces a thyrotropin-like substance. Additionally, hCG itself has weak intrinsic thyrotropic activity due to the shared alpha-subunit with TSH, which can lead to a slight decrease in maternal TSH levels during the first trimester. * **C. Chorionic corticotropin (hCC):** The placenta produces a molecule identical to ACTH (Corticotropin) and its precursor, POMC. This contributes to the physiological hypercortisolism seen in pregnancy. ### **High-Yield NEET-PG Pearls** * **The Alpha Subunit Rule:** hCG, TSH, LH, and FSH all share an identical **alpha subunit**. Specificity is determined by the **beta subunit**. * **Placental Analogs:** The placenta produces analogs for almost all pituitary hormones: * Growth Hormone analog → **Human Placental Lactogen (hPL)** / Human Chorionic Somatomammotropin. * GnRH analog → **Placental GnRH**. * CRH analog → **Placental CRH** (acts as a "placental clock" for labor). * **Steroidogenesis:** The placenta is an "incomplete" endocrine unit; it lacks the enzyme **17α-hydroxylase** and therefore cannot convert progesterone to estrogens without fetal adrenal precursors (DHEAS).

Question 74: Estrogen secretion is maximum at which phase of the menstrual cycle?

A. Just before menopause
B. At puberty
C. At menstruation
D. Before ovulation (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Before ovulation** **Medical Concept:** Estrogen levels fluctuate significantly throughout the menstrual cycle, driven by follicular development. During the **follicular phase**, the selection of a dominant follicle leads to a massive increase in estradiol production by the granulosa cells (via the aromatization of androgens). Estrogen levels reach their absolute **peak approximately 24–36 hours before ovulation**. This "pre-ovulatory surge" is critical because it triggers the switch from negative to positive feedback on the pituitary, resulting in the **LH surge**, which ultimately induces ovulation. A second, smaller peak of estrogen occurs during the mid-luteal phase, secreted by the corpus luteum. **Why other options are incorrect:** * **A. Just before menopause:** This period (perimenopause) is characterized by declining ovarian reserve and erratic, generally lower levels of estrogen as cycles become anovulatory. * **B. At puberty:** While estrogen levels rise during puberty (gonadarche), they do not reach the cyclical peaks seen in a mature, ovulating female. * **C. At menstruation:** During the menstrual phase, both estrogen and progesterone levels are at their **lowest point** due to the regression of the corpus luteum from the previous cycle. **High-Yield NEET-PG Pearls:** * **Two Peaks of Estrogen:** Remember that estrogen has a **bimodal** secretion pattern: the 1st (highest) peak is pre-ovulatory; the 2nd (lower) peak is mid-luteal. * **Progesterone Peak:** Unlike estrogen, progesterone has only **one peak**, occurring during the mid-luteal phase (Day 21 of a 28-day cycle). * **Positive Feedback:** Estrogen must maintain a concentration of >200 pg/mL for approximately 48 hours to trigger the LH surge.

Question 75: Which of the following increases significantly as pregnancy advances?

A. Tidal volume (Correct Answer)
B. Respiratory rate
C. Functional residual capacity
D. Residual volume

Explanation: **Explanation:** During pregnancy, the respiratory system undergoes significant physiological adaptations to meet the increased oxygen demands of the fetus and the mother. **1. Why Tidal Volume (TV) is correct:** The most significant change in respiratory physiology during pregnancy is an **increase in Tidal Volume (by approximately 30–40%)**. This is primarily driven by **Progesterone**, which acts as a direct respiratory stimulant. It increases the sensitivity of the central respiratory center to CO2, leading to deeper breaths (hyperventilation of pregnancy). This ensures efficient gas exchange and creates a CO2 gradient that favors the transfer of fetal CO2 to the maternal circulation. **2. Why other options are incorrect:** * **Respiratory Rate (RR):** Contrary to common belief, the RR remains **largely unchanged** or increases only very slightly. The increase in Minute Ventilation is almost entirely due to the increase in Tidal Volume, not the rate. * **Functional Residual Capacity (FRC) & Residual Volume (RV):** These **decrease** (by about 20%) as pregnancy advances. This occurs because the enlarging uterus displaces the diaphragm upwards (by ~4 cm), reducing the resting volume of the lungs. **High-Yield NEET-PG Pearls:** * **Vital Capacity (VC):** Remains **unchanged** because the decrease in FRC is compensated by the increase in Tidal Volume. * **Acid-Base Balance:** Pregnancy is a state of **Chronic Compensated Respiratory Alkalosis** (due to hyperventilation lowering $PCO_2$). * **Oxygen Consumption:** Increases by 20% due to fetal and placental metabolic needs. * **Dyspnea of Pregnancy:** A common physiological finding (affecting ~75% of women) due to the hyperstimulatory effect of progesterone and decreased $PCO_2$.

Question 76: Fetal respiratory movements occur earliest at which gestational age?

A. 12 weeks
B. 16 weeks
C. 20 weeks
D. 11 weeks (Correct Answer)

Explanation: **Explanation:** **Correct Option: D (11 weeks)** Fetal breathing movements (FBM) are essential for normal lung development and the strengthening of respiratory muscles (diaphragm and intercostals). While primitive chest wall movements can be detected via high-resolution ultrasound as early as **10–11 weeks of gestation**, 11 weeks is the standard clinical milestone cited in major physiology and OBGYN textbooks (e.g., Ganong, Williams). These movements are irregular and episodic initially, occurring primarily during rapid eye movement (REM) sleep. **Analysis of Incorrect Options:** * **Option A (12 weeks):** While very close, 11 weeks is the earliest documented onset. By 12 weeks, the movements are more established but not the "earliest." * **Option B (16 weeks):** By this stage, FBM are more frequent, but they have already been occurring for over a month. * **Option C (20 weeks):** This is the midpoint of pregnancy. At this stage, FBM are well-developed and are used as a component of the fetal biophysical profile later in pregnancy, but it is far past the point of origin. **High-Yield Clinical Pearls for NEET-PG:** * **Function:** FBM are crucial for the circulation of amniotic fluid into the lungs, providing the mechanical stretch required for alveolar growth. * **Regulation:** FBM are inhibited by **hypoxia** and **hypoglycemia** (unlike adults, where hypoxia stimulates breathing). * **Diurnal Variation:** FBM frequency increases after maternal meals and during the night. * **Biophysical Profile (BPP):** In the third trimester, the presence of at least one episode of FBM lasting $\geq$ 30 seconds within a 30-minute window is considered a normal score (2 points).

Question 77: Which ion is responsible for preventing polyspermy at the time of fertilization in mammals?

A. Na+
B. K+
C. Ca++ (Correct Answer)
D. Mg++

Explanation: **Explanation:** The prevention of polyspermy in mammals primarily occurs through the **Cortical Reaction** (the "slow block"). When a sperm cell fuses with the oocyte's plasma membrane, it triggers a rapid increase in the concentration of **intracellular Calcium (Ca++)** within the oocyte. 1. **Why Ca++ is correct:** The rise in cytosolic Ca++ (released from the endoplasmic reticulum) is the pivotal signal for fertilization. This calcium wave triggers **exocytosis of cortical granules** into the perivitelline space. These granules contain enzymes (like ovastacin) that proteolytically modify the zona pellucida (ZP3 receptors) and harden it, making it impenetrable to other sperm. This process is known as the **Zona Reaction**. 2. **Why other options are incorrect:** * **Na+:** In some non-mammalian species (like sea urchins), a Na+ influx causes a "fast block" by depolarizing the membrane. However, this has not been definitively proven to occur or be significant in human/mammalian fertilization. * **K+ and Mg++:** These ions do not play a primary signaling role in the cortical reaction or the structural modification of the zona pellucida. **High-Yield Facts for NEET-PG:** * **Fast Block:** Electrical depolarization (Na+ dependent); occurs in amphibians/sea urchins, not significant in mammals. * **Slow Block:** Cortical/Zona reaction (Ca++ dependent); the definitive mechanism in mammals. * **Oocyte Activation:** The same Ca++ spike is also responsible for the completion of **Meiosis II** in the secondary oocyte, leading to the formation of the second polar body and the definitive ovum. * **Zinc Sparks:** Recent research highlights that "sparks" of Zinc ions are also released alongside Ca++ during fertilization to assist in cell cycle resumption.

Question 78: During pregnancy, at what point is the maximum urinary human chorionic gonadotropin (hCG) level typically reached?

A. 30 days of gestation
B. 50 days of gestation
C. 70 days of gestation (Correct Answer)
D. 90 days of gestation

Explanation: **Explanation:** Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone secreted by the syncytiotrophoblast of the placenta. Its primary physiological role is to maintain the corpus luteum, ensuring the continued secretion of progesterone until the placenta takes over steroidogenesis (the luteal-placental shift). **Why 70 days is correct:** hCG levels become detectable in maternal serum/urine approximately 8–11 days after conception. The levels rise exponentially, doubling every 48–72 hours. The peak concentration of hCG is typically reached between **8 to 11 weeks of gestation** (60 to 80 days). Therefore, **70 days** (10 weeks) represents the median point of this peak physiological window. After this peak, levels decline to a lower, stable plateau for the remainder of the pregnancy. **Analysis of Incorrect Options:** * **30 days:** At this stage (approx. 4 weeks), hCG is rising rapidly but is still in the early phase of secretion. * **50 days:** While levels are high at 7 weeks, they have not yet reached the maximum peak seen at 10 weeks. * **90 days:** By 12–13 weeks, hCG levels have already begun their characteristic decline from the peak. **High-Yield Clinical Pearls for NEET-PG:** * **Structure:** hCG is a heterodimer. The **α-subunit** is identical to LH, FSH, and TSH; the **β-subunit** is unique and confers biological specificity (this is why pregnancy tests target the β-subunit). * **Doubling Time:** In a healthy intrauterine pregnancy, β-hCG levels should increase by at least 66% every 48 hours. * **Clinical Significance of High hCG:** Abnormally high levels are associated with **Molar pregnancy**, Multiple gestations, and Down Syndrome (Trisomy 21). * **Clinical Significance of Low hCG:** Abnormally low or slow-rising levels suggest Ectopic pregnancy or impending Spontaneous Abortion.

Question 79: Which of the following decreases during pregnancy?

A. Systemic venous resistance (Correct Answer)
B. Cardiac output (CO)
C. Heart rate (HR)
D. Plasma volume

Explanation: ### Explanation In pregnancy, the maternal cardiovascular system undergoes significant adaptation to meet the metabolic demands of the fetus. **1. Why Systemic Vascular Resistance (SVR) Decreases:** The hallmark of cardiovascular change in pregnancy is a **marked decrease in Systemic Vascular Resistance (SVR)**. This occurs due to: * **Progesterone:** Acts as a potent smooth muscle relaxant, causing vasodilation. * **Nitric Oxide & Prostaglandins:** Increased production leads to further vasodilation. * **Low-resistance Circuit:** The placenta acts as a high-flow, low-resistance shunt. This drop in SVR leads to a compensatory increase in cardiac output and a physiological drop in blood pressure during the second trimester. **2. Analysis of Incorrect Options:** * **Cardiac Output (CO):** Increases by 30–50%. This is achieved through increases in both stroke volume (early pregnancy) and heart rate (late pregnancy). * **Heart Rate (HR):** Increases by approximately 10–20 beats per minute to maintain the elevated cardiac output. * **Plasma Volume:** Increases significantly (up to 50%). Since the increase in plasma volume exceeds the increase in red cell mass, it leads to **"Physiological Anemia of Pregnancy."** **3. NEET-PG High-Yield Pearls:** * **Blood Pressure:** Diastolic BP decreases more than Systolic BP; the lowest point is reached at 24–28 weeks. * **Stroke Volume:** Increases early in pregnancy (peaking at 20–24 weeks). * **Uterine Blood Flow:** Increases from ~50 mL/min to ~500–750 mL/min at term. * **Coagulation:** Pregnancy is a **hypercoagulable state** (increase in Factors VII, VIII, IX, X, and Fibrinogen; decrease in Protein S).

Question 80: The corpus luteum exhibits maximum activity around which day of the menstrual cycle?

A. Day 7
B. Day 9
C. Day 11
D. Day 22 (Correct Answer)

Explanation: **Explanation:** The **corpus luteum** is a temporary endocrine structure formed from the remnants of the ovarian follicle after ovulation. Its primary function is to secrete high levels of **progesterone** (and some estrogen) to prepare the endometrium for potential implantation. **Why Day 22 is correct:** In a standard 28-day menstrual cycle, ovulation typically occurs on **Day 14**. Following ovulation, the corpus luteum begins to develop and reaches its peak size and functional maturity (maximum secretory activity) approximately **7 to 9 days after ovulation**. This corresponds to **Day 21–23** of the cycle (average Day 22). At this point, progesterone levels reach their zenith, coinciding with the "implantation window." **Analysis of Incorrect Options:** * **Day 7:** This occurs during the early proliferative phase. The follicle is still maturing under the influence of FSH; the corpus luteum does not yet exist. * **Day 9:** This is the mid-proliferative phase. Estrogen is rising, but the corpus luteum only forms post-ovulation. * **Day 11:** This is the late proliferative phase (pre-ovulatory). The dominant follicle is preparing for the LH surge. **High-Yield Clinical Pearls for NEET-PG:** * **Life Span:** If fertilization does not occur, the corpus luteum has a fixed lifespan of approximately **14 days** (the luteal phase is the most constant phase of the cycle). * **Rescue:** If pregnancy occurs, **hCG** (Human Chorionic Gonadotropin) from the syncytiotrophoblast "rescues" the corpus luteum, maintaining it until the placenta takes over progesterone production (around 8–10 weeks). * **Luteolysis:** In the absence of hCG, the corpus luteum degenerates into a connective tissue scar called the **corpus albicans**. * **Hormone Marker:** Serum progesterone levels measured on **Day 21** are clinically used to confirm that ovulation has occurred.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free