Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 171: When there is no fertilization of the ovum, the endometrial cells undergo apoptosis because:

A. The involution of the corpus luteum causes estradiol and progesterone levels to fall dramatically. (Correct Answer)
B. LH levels rise after ovulation.
C. Estradiol levels are not involved in the LH surge phenomenon.
D. Estradiol inhibits the induction of the progesterone receptor in the endometrium.

Explanation: ### Explanation **1. Why Option A is Correct:** The menstrual cycle is governed by the hormonal output of the ovaries. After ovulation, the ruptured follicle transforms into the **corpus luteum**, which secretes high amounts of **progesterone** and **estradiol**. These hormones maintain the endometrial lining in a secretory state, optimized for implantation. If fertilization does not occur, the corpus luteum has a finite lifespan of about 14 days, after which it undergoes **luteolysis** (involution). This leads to a precipitous drop in estrogen and progesterone levels. The withdrawal of these "trophic" hormones triggers enzymatic degradation of the extracellular matrix and **apoptosis** of the endometrial cells, resulting in menstruation. **2. Why the Other Options are Incorrect:** * **Option B:** LH levels actually **fall** during the luteal phase due to negative feedback from high progesterone levels. A rise in LH occurs *before* ovulation (LH surge), not after. * **Option C:** This is physiologically incorrect. Estradiol is the primary trigger for the **LH surge** via a positive feedback mechanism once it reaches a specific threshold (approx. 200 pg/mL for 48 hours). * **Option D:** In reality, **estradiol induces** the expression of progesterone receptors in the endometrium. This "priming" effect is essential for progesterone to exert its secretory effects. **3. NEET-PG High-Yield Pearls:** * **The "Hormonal Trigger":** Progesterone withdrawal is the most critical event leading to the spiral artery vasoconstriction and endometrial shedding. * **Lifespan:** The corpus luteum is "rescued" only if fertilization occurs, by **hCG** (Human Chorionic Gonadotropin) produced by the syncytiotrophoblast, which mimics LH. * **Key Enzyme:** Caspases are the executioner enzymes involved in the apoptosis of the functionalis layer during menstruation.

Question 172: Ovulation is due to surge of:

A. FSH
B. LH (Correct Answer)
C. Prolactin
D. TSH

Explanation: **Explanation:** The correct answer is **LH (Luteinizing Hormone)**. **Mechanism of Ovulation:** Ovulation is primarily triggered by the **LH surge**. In the late follicular phase, rising levels of Estrogen (secreted by the dominant Graafian follicle) exert a **positive feedback** effect on the anterior pituitary once a threshold level (>200 pg/mL for ~48 hours) is reached. This results in a massive release of LH. The LH surge initiates the final maturation of the oocyte, stimulates the production of proteolytic enzymes (like collagenase) to weaken the follicular wall, and induces the rupture of the follicle, releasing the secondary oocyte. **Analysis of Incorrect Options:** * **FSH (Follicle Stimulating Hormone):** While there is a simultaneous FSH surge (due to GnRH stimulation), its primary role is the recruitment and growth of ovarian follicles. It is not the primary trigger for the rupture of the follicle. * **Prolactin:** High levels of prolactin actually *inhibit* ovulation by suppressing GnRH secretion, which is why hyperprolactinemia often leads to amenorrhea and infertility. * **TSH (Thyroid Stimulating Hormone):** TSH regulates thyroid function. While thyroid disorders can affect the menstrual cycle, TSH has no direct role in the acute process of ovulation. **High-Yield NEET-PG Pearls:** * **Timing:** Ovulation occurs approximately **24–36 hours after the LH surge** begins and **10–12 hours after the LH peak**. * **Meiosis:** The LH surge triggers the completion of **Meiosis I** (converting the primary oocyte to a secondary oocyte) and arrests the cell in **Metaphase of Meiosis II**. * **Predictor:** Measuring urinary LH levels is the most reliable clinical method for predicting the timing of ovulation in fertility monitoring.

Question 173: Hormones FSH and LH of the anterior pituitary gland act on which of the following?

A. Testis but not ovaries
B. Ovaries but not testis
C. Both testis and ovaries (Correct Answer)
D. Adrenal cortex

Explanation: ### Explanation **Core Concept: The Hypothalamic-Pituitary-Gonadal (HPG) Axis** FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone) are collectively known as **gonadotropins**. They are synthesized and secreted by the gonadotroph cells of the anterior pituitary in response to GnRH from the hypothalamus. Their primary physiological role is to regulate the function of the **gonads** (both testes and ovaries), making Option C the correct answer. **Mechanism of Action:** * **In Females (Ovaries):** FSH stimulates the growth of ovarian follicles and the activity of aromatase (converting androgens to estrogens). LH triggers ovulation and maintains the corpus luteum for progesterone production. * **In Males (Testis):** FSH acts on **Sertoli cells** to support spermatogenesis. LH acts on **Leydig cells** to stimulate testosterone production. **Analysis of Incorrect Options:** * **Options A & B:** These are incorrect because gonadotropins are not sex-specific; they are essential for reproductive function in both males and females. * **Option D:** The adrenal cortex is primarily regulated by **ACTH** (Adrenocorticotropic Hormone) for cortisol production and the Renin-Angiotensin-Aldosterone System (RAAS) for mineralocorticoids. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Male Action:** **L**H acts on **L**eydig cells (Testosterone); **S**FSH acts on **S**ertoli cells (Spermatogenesis). * **Two-Cell, Two-Gonadotropin Theory:** In the ovary, LH stimulates Theca cells (Androstenedione production), while FSH stimulates Granulosa cells (Conversion to Estradiol). * **Inhibin:** Produced by Sertoli cells (males) and Granulosa cells (females), it provides negative feedback specifically to **FSH**, not LH. * **Pulsatility:** GnRH must be secreted in a pulsatile manner; continuous infusion paradoxically suppresses FSH and LH (the basis for GnRH agonist therapy in prostate cancer and endometriosis).

Question 174: Which of the following is NOT a feature of inhibin?

A. Non-steroidal water-soluble protein
B. Secreted by Graafian follicle
C. Stimulates FSH secretion (Correct Answer)
D. Increased secretion of inhibin occurs in polycystic ovarian disease

Explanation: **Explanation:** **Inhibin** is a glycoprotein hormone that plays a critical role in the negative feedback regulation of the hypothalamic-pituitary-gonadal axis. **Why Option C is the correct answer (The "NOT" feature):** The primary physiological function of inhibin is to **selectively inhibit** the secretion of **Follicle-Stimulating Hormone (FSH)** from the anterior pituitary. It does not stimulate FSH. This feedback loop is essential for regulating follicular development in females and spermatogenesis in males. **Analysis of other options:** * **Option A:** Inhibin is indeed a **non-steroidal, water-soluble glycoprotein** composed of an alpha and a beta subunit ($\alpha\beta$). * **Option B:** In females, it is primarily secreted by the **granulosa cells** of the developing antral follicles and the **Graafian follicle**. In males, it is secreted by the **Sertoli cells**. * **Option D:** In **Polycystic Ovarian Disease (PCOD/PCOS)**, there is an increased number of small antral follicles. This leads to **elevated levels of Inhibin-B**, which contributes to the characteristic suppression of FSH seen in these patients (leading to a high LH:FSH ratio). **High-Yield Clinical Pearls for NEET-PG:** * **Inhibin A vs. B:** Inhibin **B** is the primary form in the follicular phase (marker of ovarian reserve), while Inhibin **A** peaks in the luteal phase (secreted by the corpus luteum). * **Tumor Marker:** Inhibin is a highly specific tumor marker for **Granulosa Cell Tumors** of the ovary. * **Triple/Quadruple Test:** Inhibin A is measured during the second trimester of pregnancy; **elevated levels** are associated with an increased risk of **Down Syndrome (Trisomy 21)**. * **Activin:** A related protein (beta-beta dimer) that performs the opposite function—it **stimulates** FSH secretion.

Question 175: Arrange the steps of spermatogenesis in the sequence of their formation.

A. Spermatogonium > Spermatocyte > Spermatid > Spermatozoa (Correct Answer)
B. Spermatocyte > Spermatogonium > Spermatid > Spermatozoa
C. Spermatogonium > Spermatocyte > Spermatozoa > Spermatid
D. Spermatozoa > Spermatogonium > Spermatocyte > Spermatid

Explanation: ### Explanation **Underlying Medical Concept** Spermatogenesis is the process by which male germ cells develop into mature spermatozoa within the seminiferous tubules. It follows a strictly regulated chronological sequence: 1. **Spermatogonia (2n):** These are the primitive stem cells located on the basement membrane. They undergo mitosis to maintain their population and provide cells for differentiation. 2. **Spermatocytes (2n → n):** Primary spermatocytes undergo **Meiosis I** to form secondary spermatocytes. Secondary spermatocytes then undergo **Meiosis II** to form spermatids. 3. **Spermatids (n):** These are round, haploid cells that result from the completion of meiosis. 4. **Spermatozoa (n):** Through the process of **spermiogenesis** (morphological transformation without further division), spermatids develop tails and lose excess cytoplasm to become mature, motile sperm. **Analysis of Options** * **Option A is correct** as it accurately reflects the progression from stem cell to differentiated gamete. * **Option B is incorrect** because spermatogonia are the precursors to spermatocytes, not the other way around. * **Option C is incorrect** because spermatids must undergo spermiogenesis to become spermatozoa; the spermatozoa are the final product. * **Option D is incorrect** because it reverses the order, placing the mature gamete at the beginning. **High-Yield Facts for NEET-PG** * **Duration:** The entire process of spermatogenesis takes approximately **74 days**. * **Spermiogenesis vs. Spermiation:** *Spermiogenesis* is the transformation of spermatids to spermatozoa. *Spermiation* is the release of mature spermatozoa from Sertoli cells into the tubule lumen. * **Hormonal Control:** LH stimulates **Leydig cells** to produce Testosterone; FSH stimulates **Sertoli cells** to support spermatogenesis. * **Blood-Testis Barrier:** Formed by tight junctions between Sertoli cells, protecting developing germ cells (spermatocytes onwards) from the immune system.

Question 176: Sertoli cells have receptors for which of the following hormones?

A. Inhibin
B. Luteinizing hormone
C. Follicle stimulating hormone (Correct Answer)
D. Melatonin

Explanation: **Explanation:** The correct answer is **Follicle Stimulating Hormone (FSH)**. Sertoli cells, often called "nurse cells," are located within the seminiferous tubules and are essential for spermatogenesis. **1. Why FSH is correct:** Sertoli cells are the primary targets for FSH in the male reproductive system. When FSH binds to its G-protein coupled receptors on the Sertoli cell membrane, it stimulates the production of **Androgen Binding Protein (ABP)**, which maintains high local testosterone levels, and **Inhibin**, which provides negative feedback to the anterior pituitary. FSH also promotes the synthesis of nutrients and growth factors required for the maturation of germ cells. **2. Why other options are incorrect:** * **Inhibin:** This is a hormone **produced by** Sertoli cells, not one they have receptors for. It acts on the anterior pituitary to specifically inhibit FSH secretion. * **Luteinizing Hormone (LH):** LH receptors are located on **Leydig cells** (interstitial cells), where LH stimulates the production of testosterone. A common mnemonic is **L**H acts on **L**eydig cells. * **Melatonin:** While melatonin can influence the hypothalamic-pituitary-gonadal axis (typically inhibitory), Sertoli cells are not its primary physiological target in the context of direct hormonal regulation of spermatogenesis. **Clinical Pearls for NEET-PG:** * **Blood-Testis Barrier:** Formed by tight junctions between adjacent Sertoli cells; it protects developing sperm from the immune system. * **Müllerian Inhibiting Substance (MIS):** Also secreted by Sertoli cells in the fetus to cause regression of Müllerian ducts. * **Spermiation:** The process of releasing mature spermatozoa from Sertoli cells into the lumen of seminiferous tubules. * **Hormonal Control:** Spermatogenesis requires both **FSH** (acting on Sertoli cells) and **Testosterone** (produced by Leydig cells under LH influence).

Question 177: What is the normal pH range of amniotic fluid?

A. 6.8 to 6.9
B. 8.1 to 8.3
C. 7.4 to 7.6 (Correct Answer)
D. 6.7 to 6.8

Explanation: **Explanation:** The correct answer is **C (7.4 to 7.6)**. Amniotic fluid is a dynamic medium that surrounds the fetus, serving protective and metabolic functions. In a normal pregnancy, amniotic fluid is **slightly alkaline**, with a pH ranging from 7.0 to 7.5, typically stabilizing between **7.4 and 7.6**. This alkalinity is primarily due to the composition of the fluid, which includes fetal urine (which becomes less acidic as the kidneys mature) and secretions from the fetal respiratory tract and umbilical cord. **Analysis of Options:** * **Options A and D (6.7 to 6.9):** These values are acidic. Amniotic fluid is not normally acidic. In fact, the alkaline nature of amniotic fluid is a key diagnostic feature used to distinguish it from vaginal secretions (which are acidic, pH 3.8–4.5) during a Nitrazine test for the rupture of membranes. * **Option B (8.1 to 8.3):** This range is too basic. While the fluid is alkaline, it does not reach such high levels under physiological conditions. **Clinical Pearls for NEET-PG:** 1. **Nitrazine Test:** This is a high-yield clinical application. When amniotic fluid (pH >7.0) leaks into the vagina, it turns Nitrazine paper from yellow to **blue**. 2. **Fern Test:** Due to the high concentration of sodium chloride, amniotic fluid creates a "ferning" pattern when dried on a slide, confirming the Rupture of Membranes (ROM). 3. **Volume Dynamics:** Amniotic fluid volume peaks at approximately **800–1000 ml at 34–36 weeks** and decreases to about 600 ml at term (40 weeks). 4. **Specific Gravity:** It has a low specific gravity, approximately **1.008 to 1.010**.

Question 178: What is the action of oxytocin, except?

A. Increased contractility of the uterus
B. Contraction of myoepithelial cells
C. Milk ejection
D. Contraction of the lower uterine segment (Correct Answer)

Explanation: ### Explanation Oxytocin is a peptide hormone synthesized in the **paraventricular nucleus** of the hypothalamus and secreted by the posterior pituitary. Its primary role is to stimulate smooth muscle contraction in specific reproductive tissues. **Why Option D is the Correct Answer:** During labor, oxytocin promotes **fundal dominance**. It causes strong, rhythmic contractions of the **upper segment** of the uterus (the fundus and body) while simultaneously causing the **lower uterine segment to relax and thin out**. This physiological gradient is essential to push the fetus downward and allow the cervix to dilate. If the lower segment contracted along with the upper segment, the fetus would be trapped, and the cervix would not dilate. **Analysis of Incorrect Options:** * **Option A (Increased contractility):** Oxytocin increases the force and frequency of uterine contractions by increasing intracellular calcium and stimulating prostaglandin synthesis. * **Option B & C (Myoepithelial cells/Milk ejection):** Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli. This forces milk into the larger ducts and out through the nipple, a process known as the **Milk Ejection Reflex** (or "let-down" reflex). **High-Yield Clinical Pearls for NEET-PG:** * **Ferguson Reflex:** A neuroendocrine reflex where vaginal/cervical stretching triggers oxytocin release, creating a positive feedback loop during labor. * **Receptor Regulation:** Estrogen **upregulates** oxytocin receptors (increasing sensitivity at term), while progesterone **downregulates** them. * **Clinical Use:** Synthetic oxytocin (Pitocin) is the drug of choice for **Induction of Labor** and the prevention/treatment of **Postpartum Hemorrhage (PPH)**. * **Side Effect:** At high doses, oxytocin has an **ADH-like effect**, which can lead to water intoxication and hyponatremia.

Question 179: Which of the following can be used to evaluate ovulation?

A. Cervical mucous (Correct Answer)
B. Cervical colour
C. Cervical dilation
D. Cervical effacement

Explanation: **Explanation:** The correct answer is **Cervical mucous**. Evaluation of cervical mucus is a reliable clinical indicator of the ovulatory phase due to the influence of fluctuating ovarian hormones. 1. **Why Cervical Mucous is Correct:** Under the influence of high **estrogen** levels just before ovulation, the cervical mucus undergoes characteristic changes to facilitate sperm transport. It becomes **profuse, thin, watery, and alkaline**. Two specific tests evaluate this: * **Spinnbarkeit Effect:** The mucus becomes highly elastic and can be stretched into a long thread (usually >6 cm). * **Ferning Pattern:** When dried on a slide, the high sodium chloride content causes the mucus to crystallize in a "fern-like" pattern. Post-ovulation, progesterone makes the mucus thick, tacky, and cellular, abolishing these features. 2. **Why Other Options are Incorrect:** * **Cervical Colour:** Changes in cervical color (e.g., **Chadwick’s sign**, where the cervix turns bluish) are signs of increased vascularity associated with **pregnancy**, not ovulation. * **Cervical Dilation and Effacement:** These are clinical parameters used to assess the progress of **labor**. While minor softening occurs during ovulation, dilation and effacement are not standard or reliable methods for evaluating the ovulatory cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Best indicator of ovulation:** Mid-luteal phase **Serum Progesterone** levels (>3 ng/ml). * **Gold standard for timing ovulation:** Serial Transvaginal Ultrasound (TVS) to monitor follicular disappearance. * **LH Surge:** Occurs 24–36 hours before ovulation; it is the basis for home ovulation predictor kits. * **Basal Body Temperature (BBT):** Increases by 0.5–1.0°F after ovulation due to the thermogenic effect of progesterone.

Question 180: If the corpus luteum is functioning, its endocrine function is initiated by the influence of which of the following hormones?

A. LH (Correct Answer)
B. FSH
C. GnRH
D. All of the above

Explanation: **Explanation:** The **Corpus Luteum (CL)** is a temporary endocrine structure formed from the remnants of the Graafian follicle after ovulation. Its primary function is the secretion of progesterone and estrogen to maintain the endometrial lining for potential implantation. **Why LH is the Correct Answer:** The initiation and maintenance of the corpus luteum are strictly dependent on **Luteinizing Hormone (LH)**. Following the LH surge, which triggers ovulation, the remaining granulosa and theca cells undergo "luteinization." LH stimulates these cells to increase their expression of steroidogenic enzymes, effectively turning the follicle into a progesterone-producing factory. Without the continuous trophic support of LH (or hCG in pregnancy), the corpus luteum would undergo luteolysis (degeneration). **Why Other Options are Incorrect:** * **FSH (Follicle Stimulating Hormone):** While FSH is crucial for the recruitment and growth of follicles during the follicular phase, it does not initiate the endocrine function of the corpus luteum. * **GnRH (Gonadotropin-Releasing Hormone):** GnRH is the upstream hypothalamic hormone that stimulates the release of LH and FSH from the anterior pituitary. It does not act directly on the ovary to initiate luteal function. **High-Yield Clinical Pearls for NEET-PG:** * **Luteal Phase Length:** The lifespan of the corpus luteum is remarkably constant at approximately **14 days** in a non-pregnant cycle. * **Rescue of Corpus Luteum:** If fertilization occurs, **hCG** (Human Chorionic Gonadotropin), which is an analog of LH, binds to LH receptors to "rescue" the corpus luteum, maintaining progesterone production until the placenta takes over (the **luteal-placental shift** at 7–9 weeks). * **Hormone Secretion:** The corpus luteum secretes **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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