Reproductive Physiology Practice Questions

Q: Maximum fertilizable life span of an oocyte is:

24 hours. **Explanation:** The fertilizable life span of an oocyte refers to the duration after ovulation during which the secondary oocyte remains viable and capable of being fertilized by a sperm. 1. **Why 24 hours is correct:** After ovulation, the secondary oocyte is picked up by the fimbriae and moves into the ampulla of the fallopian tube. Its viability is relatively short-lived. Most physiological studies and standard textbooks (like Guyton and Ganong) state that the human oocyte must be fertilized within **12 to 24 hours** of its release. Beyond 24 hours, the oocyte undergoes degenerative changes, the zona pellucida hardens, and it loses its capacity to respond to sperm penetration. 2. **Why other options are incorrect:** * **12 hours (Option A):** While the oocyte is most fertile during the first 12 hours, its maximum window extends up to 24 hours. * **36 & 48 hours (Options C & D):** These durations are too long for an oocyte. While **spermatozoa** can survive in the female reproductive tract for 48 to 72 hours (sometimes up to 5 days), the oocyte is much more fragile and degrades significantly by the 36-hour mark. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Fertilization:** Ampulla of the Fallopian tube. * **Sperm Viability:** 48–72 hours (longer than the oocyte). * **Fertile Window:** The period starting 5 days before ovulation until 1 day after. * **Meiotic State:** At the time of ovulation, the oocyte is arrested in **Metaphase of Meiosis II**. It only completes meiosis II if fertilization occurs. * **Capacitation:** The process sperm must undergo in the female tract (taking ~7 hours) to become capable of fertilizing the oocyte.

Q: What is the effect of a higher pulse frequency of Gonadotropin-Releasing Hormone (GnRH)?

Stimulates LH preferentially. **Explanation:** The secretion of Gonadotropins (LH and FSH) from the anterior pituitary is governed by the **pulsatile release** of GnRH from the hypothalamus. The pituitary gland decodes the frequency and amplitude of these pulses to determine which hormone to secrete. **1. Why Option B is correct:** A **high-frequency** (fast) pulse of GnRH (e.g., one pulse every 60–90 minutes) favors the expression of the LH $\beta$-subunit gene, leading to the **preferential secretion of Luteinizing Hormone (LH)**. This is physiologically evident during the late follicular phase of the menstrual cycle, where increased GnRH pulse frequency contributes to the LH surge required for ovulation. **2. Why other options are incorrect:** * **Option A:** **Low-frequency** (slow) pulses of GnRH (e.g., one pulse every 120–180 minutes) preferentially stimulate the secretion of **Follicle-Stimulating Hormone (FSH)**. This occurs typically during the early follicular phase. * **Option C & D:** While GnRH is generally stimulatory, a **continuous (non-pulsatile)** infusion of GnRH leads to the downregulation (internalization) of GnRH receptors on gonadotropes. This results in a profound decrease in both LH and FSH, a process known as medical castration. **High-Yield Clinical Pearls for NEET-PG:** * **GnRH Agonists (e.g., Leuprolide):** Used in a **continuous** fashion to treat precocious puberty, prostate cancer, and endometriosis by suppressing the pituitary-gonadal axis. * **Kallmann Syndrome:** Characterized by delayed puberty and anosmia due to the failure of GnRH neurons to migrate from the olfactory placode to the hypothalamus. * **Pulse Generator:** Located in the **Arcuate nucleus** of the hypothalamus.

Q: Which of the following physiological changes occurs during pregnancy?

Tidal volume increases. **Explanation:** During pregnancy, the respiratory system undergoes significant physiological adaptations to meet the increased metabolic demands of the fetus and the mother. **1. Why Tidal Volume (TV) Increases:** Progesterone acts as a direct respiratory stimulant, increasing the sensitivity of the central respiratory center to CO2. This leads to an increase in **Tidal Volume (by ~40%)**, while the respiratory rate remains relatively constant. This increase in TV enhances minute ventilation, ensuring efficient gas exchange. **2. Analysis of Incorrect Options:** * **Arterial pO2 decreases:** Incorrect. Due to hyperventilation (increased TV), the arterial pO2 actually **increases** slightly (typically 100–105 mmHg) to facilitate oxygen transfer across the placenta. * **Cardiac output decreases:** Incorrect. Cardiac output **increases** significantly (by 30–50%) during pregnancy to support fetal growth and increased maternal blood volume. * **Respiratory acidosis:** Incorrect. The progesterone-driven hyperventilation causes a "washout" of CO2, leading to a decrease in arterial pCO2 (hypocapnia). This results in a state of **compensated respiratory alkalosis**, not acidosis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common change:** Increase in Tidal Volume. * **Lung Volumes:** Functional Residual Capacity (FRC), Residual Volume (RV), and Expiratory Reserve Volume (ERV) all **decrease** due to the upward displacement of the diaphragm by the gravid uterus. * **Vital Capacity (VC):** Remains **unchanged** because the decrease in RV is compensated by the increase in TV. * **Oxygen Dissociation Curve:** Shifts to the **right** (due to increased 2,3-DPG), favoring oxygen unloading to the fetus.

Q: The placenta secretes a hormone that participates in the stimulation of ductal growth in the mammary gland during pregnancy. Which hormone is this?

Human chorionic somatotropin (HCS). ### Explanation **Correct Option: C. Human chorionic somatotropin (HCS)** **Mechanism:** Human chorionic somatotropin (HCS), also known as **Human Placental Lactogen (hPL)**, is a protein hormone secreted by the syncytiotrophoblast of the placenta starting around the 5th week of pregnancy. It is structurally similar to growth hormone and prolactin. Its primary functions are: 1. **Metabolic:** It acts as a "maternal diabetogenic" hormone by decreasing maternal insulin sensitivity, ensuring a steady supply of glucose to the fetus. 2. **Mammary Development:** Along with estrogen and progesterone, HCS plays a crucial role in stimulating the **growth of ducts and development of alveoli** in the mammary glands to prepare for lactation. **Why other options are incorrect:** * **A. Endothelial growth factor (EGF):** While growth factors are involved in general cellular proliferation, EGF is not a primary placental hormone responsible for mammary ductal morphogenesis during pregnancy. * **B. Human chorionic gonadotropin (HCG):** Its primary role is to maintain the corpus luteum during early pregnancy to ensure continued progesterone production. It does not have a direct effect on mammary ductal growth. * **D. Relaxin:** Secreted by the corpus luteum and placenta, its main role is to soften the cervix and relax the pelvic ligaments (symphysis pubis) to facilitate delivery. **High-Yield NEET-PG Pearls:** * **HCS/hPL** is the hormone produced in the largest amount by the placenta. * Its levels are directly proportional to **placental mass**; therefore, low levels may indicate placental insufficiency. * **Mammary Growth Summary:** Estrogen stimulates **ductal** growth; Progesterone stimulates **lobulo-alveolar** development; HCS/hPL supports both. * HCS is a potent **lipolytic** agent, increasing free fatty acids in maternal blood as an alternative energy source for the mother.

Q: After how many hours of the luteinizing hormone (LH) surge does ovulation typically occur?

24-36 hours. The LH surge is the critical physiological trigger for ovulation. It initiates the resumption of meiosis I in the primary oocyte and stimulates the production of proteolytic enzymes that weaken the follicular wall [1]. **1. Why Option C is Correct:** Physiologically, ovulation occurs approximately **24 to 36 hours after the onset of the LH surge** and about **10 to 12 hours after the LH peak** [1]. This window is the standard timeframe used in clinical reproductive medicine to predict the "fertile window" and time procedures like Intrauterine Insemination (IUI). **2. Analysis of Incorrect Options:** * **Option A (24 hours):** While ovulation can occur at 24 hours, this represents the earliest part of the spectrum and does not account for the full physiological range. * **Option B (24-48 hours):** This range is slightly too broad. While the effects of progesterone rise after 48 hours, the actual mechanical release of the egg (ovulation) typically concludes by 36 hours post-surge. * **Option D (36-48 hours):** This is generally too late. By 48 hours, the follicle has usually already ruptured or is transitioning into the corpus luteum. **3. High-Yield Clinical Pearls for NEET-PG:** * **Estrogen Trigger:** The LH surge is triggered by a positive feedback loop when estradiol levels reach a threshold of **>200 pg/mL** for at least **48 hours** [2]. * **Meiosis:** The LH surge causes the oocyte to complete **Meiosis I** and arrest in **Metaphase of Meiosis II** until fertilization [1]. * **Stigma:** The small, avascular spot that forms on the ovarian surface just before rupture is called the *stigma*. * **Mittelschmerz:** Mid-cycle pelvic pain associated with ovulation due to follicular fluid or blood irritating the peritoneum.

Q: Which finding would be present following selective destruction of Sertoli cells?

Increased plasma follicle-stimulating hormone (FSH) levels. **Explanation:** The regulation of the male reproductive system involves the **Hypothalamic-Pituitary-Gonadal (HPG) axis**. Sertoli cells, located within the seminiferous tubules, play a crucial role in spermatogenesis and the feedback regulation of **Follicle-Stimulating Hormone (FSH)**. 1. **Why Option D is Correct:** Sertoli cells produce a glycoprotein hormone called **Inhibin B**. Inhibin B exerts specific negative feedback on the anterior pituitary to inhibit the secretion of FSH. When Sertoli cells are selectively destroyed, Inhibin B levels plummet. The loss of this negative feedback leads to a compensatory **increase in plasma FSH levels**. 2. **Why Other Options are Incorrect:** * **Option A & C:** Testosterone production and **Luteinizing Hormone (LH)** secretion are governed by **Leydig cells**. Since the destruction is selective to Sertoli cells, the Leydig cells remain functional. Therefore, testosterone levels remain normal, and consequently, LH levels (regulated by testosterone feedback) do not increase. * **Option B:** Inhibin is produced *by* Sertoli cells. Destruction of these cells leads to **decreased** plasma inhibin levels, not increased. **High-Yield Clinical Pearls for NEET-PG:** * **Sertoli Cells Only Syndrome (Del Castillo Syndrome):** A clinical condition where seminiferous tubules lack germ cells but contain Sertoli cells; however, if Sertoli function is impaired, FSH will be elevated despite normal LH/Testosterone. * **Blood-Testis Barrier:** Formed by tight junctions between Sertoli cells. * **Mnemonic:** **S**ertoli cells = **S**upport spermatogenesis, **S**ecrete Inhibin, and respond to F**S**H. **L**eydig cells = **L**iberate testosterone and respond to **L**H.

Q: Maximum prostaglandin concentration is seen in which body fluid?

Seminal fluid. **Explanation:** The correct answer is **Seminal fluid**. **1. Why Seminal Fluid is Correct:** Seminal fluid contains the highest concentration of prostaglandins in the human body (approximately 100–300 µg/mL). These are primarily secreted by the **seminal vesicles**. Prostaglandins (specifically PGE and PGF series) play a crucial role in male fertility by: * Reacting with female cervical mucus to make it more receptive to sperm penetration. * Stimulating reverse peristaltic contractions in the uterus and fallopian tubes to facilitate sperm transport toward the ovum. **2. Why Other Options are Incorrect:** * **Amniotic fluid:** While prostaglandins are present here and increase significantly during labor (to help with cervical ripening and uterine contractions), the concentration remains much lower than that found in semen. * **Tears and Saliva:** These fluids contain only trace amounts of prostaglandins, primarily acting as local inflammatory mediators or protective factors, but they are not major storage or secretory sites. **3. High-Yield Clinical Pearls for NEET-PG:** * **Source:** 60% of semen volume comes from seminal vesicles, which provide fructose (energy) and prostaglandins. * **Clinical Significance:** Low prostaglandin levels in semen are associated with certain types of male infertility. * **Prostaglandin Synthesis:** They are derived from **arachidonic acid** via the cyclooxygenase (COX) pathway. * **Uterine Effect:** Seminal prostaglandins cause the female reproductive tract to contract "upwards," aiding sperm motility—a process often tested in reproductive physiology.

Q: What is the normal sperm count?

60-120 million/mL. ### Explanation **1. Understanding the Correct Answer (Option D)** The normal sperm count in a healthy adult male typically ranges from **60 to 120 million per milliliter (mL)** of semen. According to standard physiological texts (like Guyton and Ganong), a count below 20 million/mL is generally associated with infertility (oligozoospermia). It is crucial to note the units: sperm density is measured per **mL of ejaculate**, not per cubic millimeter (mm³). **2. Analysis of Incorrect Options** * **Options A & C (Lakh/mm³):** These options use "lakh" (a common Indian unit) and "mm³." While 60–120 lakh equals 6–12 million, the volume unit **mm³** is incorrect for semen analysis. One mL is equal to 1,000 mm³; therefore, a count in mm³ would be numerically much smaller. * **Option B (4-5 million/mm³):** This is a "distractor" value. 4.5 to 5.5 million/mm³ is the normal range for **Red Blood Cell (RBC) count** in adult males. Students often confuse these two physiological constants during the exam. **3. High-Yield Clinical Pearls for NEET-PG** * **WHO 2021 Criteria (6th Ed):** While physiological ranges are broad, the WHO lower reference limit for sperm concentration is **15 million/mL**. * **Terminology:** * **Oligozoospermia:** <15-20 million/mL. * **Azoospermia:** Total absence of sperm in ejaculate. * **Aspermia:** Absence of ejaculate volume. * **Asthenozoospermia:** Reduced sperm motility. * **Teratozoospermia:** Abnormal sperm morphology. * **Volume:** Normal ejaculate volume is **1.5 to 5 mL**. * **pH:** Semen is slightly alkaline (**7.2–8.0**), which helps neutralize the acidic vaginal environment.

Question 1

Maximum fertilizable life span of an oocyte is:

Accepted Answer

24 hours

Answer

12 hours

Answer

36 hours

Answer

48 hours

Question 2

What is the effect of a higher pulse frequency of Gonadotropin-Releasing Hormone (GnRH)?

Accepted Answer

Stimulates LH preferentially

Answer

Stimulates FSH preferentially

Answer

Decreases both FSH and LH

Answer

Decreases LH preferentially

Question 3

Which of the following physiological changes occurs during pregnancy?

Accepted Answer

Tidal volume increases

Answer

Arterial pO2 decreases

Answer

Cardiac output decreases

Answer

Respiratory acidosis

Question 4

The placenta secretes a hormone that participates in the stimulation of ductal growth in the mammary gland during pregnancy. Which hormone is this?

Accepted Answer

Human chorionic somatotropin (HCS)

Answer

Endothelial growth factor (EGF)

Answer

Human chorionic gonadotropin (HCG)

Answer

Relaxin

Question 5

Which of the following is seen in the ovulatory phase?

Accepted Answer

Stimulation of continuation of reduction division of oocytes

Answer

Inhibin A is increased

Answer

FSH increases steroid synthesis in granulosa cells

Answer

Activin causes FSH to act on granulosa cells

Question 6

After how many hours of the luteinizing hormone (LH) surge does ovulation typically occur?

Accepted Answer

24-36 hours

Answer

24 hours

Answer

24-48 hours

Answer

36-48 hours

Question 7

Which finding would be present following selective destruction of Sertoli cells?

Accepted Answer

Increased plasma follicle-stimulating hormone (FSH) levels

Answer

Increased plasma testosterone levels

Answer

Increased plasma inhibin levels

Answer

Increased plasma luteinizing hormone (LH) levels

Question 8

Apoptosis can occur by change in hormone levels in the ovarian cycle. When there is no fertilization of the ovum, the endometrial cells die because:

Accepted Answer

The involution of corpus luteum causes estradiol and progesterone levels to fall dramatically.

Answer

LH levels rise after ovulation.

Answer

Estradiol levels are not involved in the LH surge phenomenon.

Answer

Estradiol inhibits the induction of the progesterone receptor in the endometrium.

Question 9

Maximum prostaglandin concentration is seen in which body fluid?

Accepted Answer

Seminal fluid

Answer

Amniotic fluid

Answer

Tear

Answer

Saliva

Question 10

What is the normal sperm count?

Accepted Answer

60-120 million/mL

Answer

60-100 lakh/mm3

Answer

4-5 million/mm3

Answer

60-120 lakh/mm3

Reproductive Physiology — MCQs

Reproductive Physiology — MCQs

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