Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 221: Which hormone produced by the human placenta has LH-like activity?

A. Progesterone
B. Testosterone
C. Human chorionic gonadotropin (Correct Answer)
D. Luteinizing hormone

Explanation: **Explanation:** **Human Chorionic Gonadotropin (hCG)** is a glycoprotein hormone secreted by the syncytiotrophoblast of the placenta. It is structurally a heterodimer consisting of an alpha (α) and a beta (β) subunit. The α-subunit is identical to that of LH, FSH, and TSH; however, the **β-subunit of hCG is structurally very similar to the β-subunit of Luteinizing Hormone (LH)**. Due to this structural homology, hCG binds to the same **LH/hCG receptors**. Its primary physiological role is to "rescue" the corpus luteum from involution, maintaining progesterone production until the placenta takes over (the luteal-placental shift). **Analysis of Incorrect Options:** * **Progesterone:** A steroid hormone produced by the corpus luteum and later the placenta. It maintains the uterine lining but does not possess gonadotropic activity. * **Testosterone:** An androgenic steroid. While hCG stimulates Leydig cells in the male fetus to produce testosterone, testosterone itself does not have LH-like properties. * **Luteinizing Hormone (LH):** Produced by the anterior pituitary, not the placenta. While it has the same activity, the question specifically asks for a hormone *produced by the placenta*. **Clinical Pearls for NEET-PG:** * **Doubling Time:** In early normal pregnancy, hCG levels double approximately every 48 hours. * **Peak Levels:** hCG levels peak at around **8–10 weeks** of gestation and then decline to a lower plateau. * **Biological Mimicry:** Because of its LH-like activity, purified hCG is used clinically to **induce ovulation** in infertility treatments (acting as a surrogate LH surge). * **Thyroid Link:** At very high levels (e.g., Hydatidiform mole), hCG can bind to TSH receptors, potentially causing hyperthyroidism.

Question 222: Which of the following is the cause of amenorrhea in a lactating mother?

A. Increased release of LH
B. Increased GnRH secretion
C. Hyperestrogenic state
D. Increased prolactin level (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Increased prolactin level.** **Mechanism of Lactational Amenorrhea:** During breastfeeding, the infant's suckling stimulus triggers the release of **Prolactin** from the anterior pituitary. While prolactin is essential for milk production, high levels exert a potent inhibitory effect on the reproductive axis. Specifically, prolactin inhibits the pulsatile secretion of **GnRH (Gonadotropin-Releasing Hormone)** from the hypothalamus. Reduced GnRH leads to a suppression of **LH (Luteinizing Hormone)** and **FSH (Follicle-Stimulating Hormone)** release from the pituitary. Without the LH surge, ovulation is inhibited, resulting in amenorrhea (Lactational Amenorrhea Method). **Analysis of Incorrect Options:** * **A & B (Increased LH/GnRH):** These are incorrect because prolactin actually **suppresses** the GnRH pulse generator and the subsequent release of LH. High levels of these hormones would trigger ovulation, not amenorrhea. * **C (Hyperestrogenic state):** Lactating mothers are actually in a **hypoestrogenic** state. Because FSH and LH are suppressed, the ovarian follicles do not develop, leading to very low estrogen levels. This hypoestrogenism is also why lactating women may experience vaginal dryness. **High-Yield NEET-PG Pearls:** * **Dopamine Connection:** Dopamine is the primary "Prolactin Inhibiting Factor." Drugs that block dopamine (e.g., Metoclopramide, Antipsychotics) cause hyperprolactinemia and secondary amenorrhea. * **Kisspeptin:** Recent studies show prolactin inhibits **Kisspeptin** neurons in the hypothalamus, which is the intermediary step in suppressing GnRH. * **Contraceptive Efficacy:** The Lactational Amenorrhea Method (LAM) is only reliable if the mother is exclusively breastfeeding, is less than 6 months postpartum, and remains amenorrheic.

Question 223: Meiosis in spermatogenesis occurs in which of the following steps?

A. Primary spermatocyte to intermediate spermatocyte
B. Primary spermatocyte to secondary spermatocyte (Correct Answer)
C. Secondary spermatocyte to round spermatid
D. Round spermatid to elongated spermatid

Explanation: ### Explanation The process of spermatogenesis involves the transformation of primitive germ cells into mature spermatozoa through a series of mitotic and meiotic divisions. **Why Option B is Correct:** The first meiotic division (**Meiosis I**) is the reductional division. It occurs when a **primary spermatocyte** (diploid, 46XY) undergoes division to form two **secondary spermatocytes** (haploid, 23X or 23Y). This is the critical step where the chromosome number is halved. **Analysis of Incorrect Options:** * **Option A:** There is no stage known as an "intermediate spermatocyte" in human spermatogenesis. The progression moves directly from Type B spermatogonia to primary spermatocytes. * **Option C:** The transition from secondary spermatocyte to round spermatid is **Meiosis II** (equational division). While this is technically a meiotic step, the question typically refers to the initiation of meiosis or the primary reductional phase. In many standardized exams, the conversion of primary to secondary is the hallmark of the meiotic phase. * **Option D:** The transformation of a round spermatid into an elongated spermatid (and eventually a mature spermatozoon) is called **Spermiogenesis**. This involves morphological changes (acrosome formation, tail development) but **no cell division**. **High-Yield Facts for NEET-PG:** * **Duration:** The entire process of spermatogenesis takes approximately **74 days**. * **Spermiation:** The process by which mature spermatozoa are released from Sertoli cells into the lumen of seminiferous tubules. * **Blood-Testis Barrier:** Formed by tight junctions between **Sertoli cells**; it protects developing germ cells (from primary spermatocytes onwards) from the immune system. * **Hormonal Control:** LH acts on Leydig cells (testosterone), while FSH acts on Sertoli cells to support spermatogenesis.

Question 224: How is iodide transported across the placenta?

A. Simple diffusion
B. Carrier-mediated process (Correct Answer)
C. Endocytosis
D. No transport

Explanation: **Explanation:** The transport of iodide across the placenta is a vital physiological process required for fetal thyroid hormone synthesis, which is essential for neurodevelopment. **1. Why "Carrier-mediated process" is correct:** Iodide does not cross the placenta by simple passive diffusion; instead, it is actively transported against a concentration gradient. This is primarily achieved through a **carrier-mediated process** involving the **Sodium-Iodide Symporter (NIS)**, located on the basal (maternal-facing) membrane of the syncytiotrophoblast. This ensures that the fetal plasma iodide concentration is generally higher than the maternal concentration, providing an adequate supply for the fetal thyroid gland, which begins functioning around the 12th week of gestation. **2. Why other options are incorrect:** * **Simple diffusion:** Iodide is a charged ion and cannot freely permeate the lipid bilayer of the placental membrane at rates sufficient to meet fetal demands. * **Endocytosis:** This mechanism is reserved for large molecules like Immunoglobulin G (IgG) or iron-bound transferrin, not for small ions like iodide. * **No transport:** This is incorrect as the fetus is entirely dependent on the maternal supply of iodide for its thyroid function; a lack of transport would lead to congenital hypothyroidism and cretinism. **Clinical Pearls for NEET-PG:** * **Wolff-Chaikoff Effect:** Excessive maternal intake of iodine can cross the placenta and temporarily inhibit fetal thyroid hormone synthesis, potentially causing a fetal goiter. * **Anti-thyroid drugs:** Drugs like Propylthiouracil (PTU) and Methimazole cross the placenta and can affect fetal thyroid status. PTU is generally preferred in the first trimester due to lower teratogenicity. * **Fetal Thyroid:** The fetal thyroid starts trapping iodine at **10–12 weeks** and becomes responsive to TSH by **20 weeks**.

Question 225: Sperm receive nutrition from which of the following?

A. Fructose (Correct Answer)
B. Glucose
C. Sucrose
D. Amylase

Explanation: **Explanation:** The correct answer is **Fructose**. **Why Fructose is Correct:** Spermatozoa require a constant energy source for motility and survival. In the male reproductive system, the **seminal vesicles** secrete a thick, alkaline fluid that constitutes about 60-70% of the total semen volume. This fluid is rich in **fructose**, which serves as the primary glycolytic fuel for sperm. Unlike most body cells that prefer glucose, sperm are specialized to utilize fructose via the GLUT-5 transporter to generate ATP through anaerobic and aerobic pathways. **Analysis of Incorrect Options:** * **B. Glucose:** While glucose can be metabolized by sperm, it is not the primary sugar found in seminal fluid. Fructose is the physiological substrate provided by the male reproductive tract. * **C. Sucrose:** This is a disaccharide (glucose + fructose). Sperm lack the extracellular enzymes (sucrase) necessary to break down sucrose into usable monosaccharides in the semen. * **D. Amylase:** This is an enzyme that breaks down starch into sugars. It is not a nutrient source and is primarily found in saliva and pancreatic secretions. **NEET-PG High-Yield Pearls:** * **Site of Production:** Fructose is produced specifically by the **seminal vesicles**. * **Clinical Significance:** The absence of fructose in a semen sample (Fructose Test) suggests **bilateral congenital absence of the vas deferens (CBAVD)** or obstruction of the ejaculatory ducts. * **Semen Composition:** Seminal vesicles provide fructose and prostaglandins; the **prostate gland** provides citrate, calcium, and acid phosphatase; and **Bulbourethral (Cowper’s) glands** provide lubricating mucus. * **Sperm Maturation:** While sperm gain the *potential* for motility in the epididymis, they only become fully motile upon ejaculation when mixed with fructose-rich seminal fluid.

Question 226: What type of uterine contraction is responsible for cervical ripening?

A. A waves
B. B waves
C. Both A and B waves
D. Neither A nor B waves (Correct Answer)

Explanation: The correct answer is **D. Neither A nor B waves.** ### **Explanation** To understand this question, we must distinguish between uterine contractions (myometrial activity) and the biochemical process of cervical ripening. 1. **Why D is correct:** Cervical ripening is primarily a **biochemical process**, not a mechanical one driven by contractions. It involves the remodeling of the cervical connective tissue, characterized by a decrease in collagen content, an increase in glycosaminoglycans (like hyaluronic acid), and increased water content. This process is mediated by hormones (Prostaglandins E2 and F2α, Estrogen) and inflammatory mediators, rather than A or B waves. 2. **Why A is incorrect:** **A waves (Alvarez waves)** are low-amplitude (2–4 mmHg), high-frequency rhythmic contractions that occur throughout pregnancy. They are localized and do not lead to cervical changes. 3. **Why B is incorrect:** **B waves (Braxton-Hicks contractions)** are high-amplitude (10–15 mmHg), low-frequency contractions. While they may help in the "effacement" or thinning of the lower uterine segment in late pregnancy, they are not the primary physiological mechanism responsible for the biochemical "ripening" of the cervix. ### **High-Yield Clinical Pearls for NEET-PG** * **Cervical Ripening Assessment:** Evaluated using the **Bishop Score** (Parameters: Dilatation, Effacement, Station, Consistency, Position). A score of $\geq 8$ suggests a "ripe" cervix. * **Pharmacology:** **Dinoprostone (PGE2)** is the gold standard pharmacological agent used for cervical ripening. * **Physiology:** During ripening, the enzyme **collagenase** breaks down the rigid collagen framework, allowing the cervix to become soft and compliant for labor. * **A vs. B Waves:** Remember, Alvarez waves are "Small & Frequent," while Braxton-Hicks are "Large & Infrequent." Neither causes true labor.

Question 227: Production of spermatozoa is essential for reproduction. With respect to the spermatozoa tail structure, what is the unit that is essential for motility?

A. Tail
B. Axoneme (Correct Answer)
C. Mitochondrial
D. Energy generating area

Explanation: **Explanation:** The correct answer is **Axoneme**. **1. Why Axoneme is correct:** The axoneme is the structural and functional core of the spermatozoon tail (flagellum). It consists of a highly organized microtubule complex, typically in a **"9+2" arrangement** (nine peripheral doublets surrounding two central singlets). The motility is driven by **dynein arms** (ATPase enzymes) attached to these microtubules, which slide against each other to create the bending motion required for forward propulsion. Without the axoneme, the mechanical movement of the sperm is impossible. **2. Why other options are incorrect:** * **Tail:** While the tail is the overall anatomical structure used for swimming, the question asks for the specific *unit* or structural component essential for motility. The "tail" is too broad a term. * **Mitochondrial / Energy generating area:** These refer to the **middle piece** of the sperm. While mitochondria provide the ATP (energy) necessary for movement, they are the "fuel source," not the "motor unit" itself. Even with ATP, motility cannot occur without the functional machinery of the axoneme. **3. High-Yield Clinical Pearls for NEET-PG:** * **Kartagener’s Syndrome:** A subset of Primary Ciliary Dyskinesia caused by a deficiency in **dynein arms** within the axoneme. This leads to immotile sperm (infertility) and respiratory issues (due to impaired cilia). * **Sperm Maturation:** While the axoneme provides the machinery for movement, sperm only acquire *actual* motility in the **epididymis**. * **Capacitation:** This process occurs in the female reproductive tract, leading to "hyperactivated motility" required for fertilization.

Question 228: Ovulation occurs:

A. 14 days after the end of menstruation
B. 14 days prior to the next menstruation (Correct Answer)
C. On the 14th day of the menstrual cycle
D. None of the above

Explanation: **Explanation:** The menstrual cycle consists of two phases: the **Follicular (Proliferative) phase** and the **Luteal (Secretory) phase**. The key to this question lies in the variability of these phases. **1. Why Option B is Correct:** The **Luteal phase is constant**, lasting almost exactly **14 days** in most women. This is because the lifespan of the *corpus luteum* is fixed; if fertilization does not occur, it regresses after 14 days, leading to a withdrawal of progesterone and the onset of menstruation. Therefore, regardless of the total cycle length (28, 35, or 21 days), ovulation consistently occurs 14 days *before* the next period begins. **2. Why Other Options are Incorrect:** * **Option A:** The duration of menstruation and the subsequent follicular phase are highly variable. Ovulation does not depend on when the previous period ended, but rather on when the next one is due. * **Option C:** This is only true in a perfect **28-day cycle**. In a 35-day cycle, ovulation occurs on Day 21 (35 minus 14). Labeling "Day 14" as the universal day of ovulation is a common clinical misconception. **High-Yield NEET-PG Pearls:** * **LH Surge:** The most reliable predictor of ovulation. Ovulation occurs **10–12 hours after the LH peak** and **32–36 hours after the onset** of the LH surge. * **Mittelschmerz Sign:** Lower abdominal pain felt mid-cycle due to follicular rupture. * **Spinnbarkeit Phenomenon:** Under estrogen influence, cervical mucus becomes thin, clear, and stretchy (like egg white) just before ovulation. * **Basal Body Temperature (BBT):** Increases by 0.5–1.0°F after ovulation due to the thermogenic effect of **Progesterone**.

Question 229: Which hormone is NOT important in the growth of the duct system of the breast?

A. Insulin
B. Growth hormone
C. Prolactin
D. Progesterone (Correct Answer)

Explanation: ### Explanation The development of the breast (mammogenesis) is a complex process involving a synergy of multiple hormones. To answer this question, one must distinguish between the development of the **ductal system** versus the **tubulo-alveolar system**. **1. Why Progesterone is the Correct Answer:** While progesterone is essential for breast development, its primary role is the development of the **lobules and alveoli** (the milk-secreting structures). It acts on the terminal ends of the ducts to cause alveolar budding. It is **not** responsible for the linear growth or branching of the ductal system itself. **2. Analysis of Incorrect Options:** * **Estrogen (Primary Driver):** Although not an option here, it is the chief hormone for ductal growth. However, it cannot act alone. * **Growth Hormone (B) and Insulin (A):** These are "permissive" metabolic hormones. They are essential for providing the metabolic framework and growth environment required for estrogen to stimulate ductal elongation. * **Prolactin (C):** While primarily known for lactogenesis, prolactin (along with GH) is necessary for the initial development of the mammary ducts. In the absence of prolactin, estrogen-mediated ductal growth is significantly impaired. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Ductal Growth:** Estrogen + GH + Prolactin + Insulin + Glucocorticoids. * **Lobulo-alveolar Growth:** Progesterone + Estrogen + Prolactin + GH + Insulin + Glucocorticoids. * **Milk Production (Lactogenesis):** Prolactin (inhibited by high Estrogen/Progesterone during pregnancy). * **Milk Ejection (Galactokinesis):** Oxytocin (via contraction of myoepithelial cells). * **Puberty:** The first sign of puberty in girls is **Thelarche** (breast budding), driven primarily by Estrogen.

Question 230: A female athlete who took testosterone-like steroids for several months stopped having normal menstrual cycles. What is the best explanation for this observation?

A. Testosterone stimulates inhibin production from the corpus luteum.
B. Testosterone binds to receptors in the endometrium, resulting in the failure of the endometrium to develop during the normal cycle.
C. Testosterone binds to receptors in the anterior pituitary that stimulate the secretion of FSH and LH.
D. Testosterone inhibits the hypothalamic secretion of GnRH and the pituitary secretion of LH and FSH. (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** The female reproductive axis is regulated by **negative feedback** mechanisms. Exogenous testosterone (or anabolic steroids) acts as a potent suppressor of the Hypothalamic-Pituitary-Ovarian (HPO) axis. * **Hypothalamus:** Testosterone inhibits the pulsatile release of **GnRH**. * **Anterior Pituitary:** It directly suppresses the secretion of **FSH and LH**. Without the cyclic rise of FSH, follicular development is arrested. Without the LH surge, ovulation cannot occur. This leads to hypoestrogenism and secondary amenorrhea, mimicking the feedback effect typically seen with high levels of progesterone or estrogen. **2. Why Other Options are Incorrect:** * **Option A:** Inhibin is primarily produced by granulosa cells (Inhibin A/B) and the corpus luteum to suppress FSH. Testosterone does not stimulate its production; rather, testosterone leads to the absence of a corpus luteum by preventing ovulation. * **Option B:** While high androgens can cause endometrial atrophy over time, the primary cause of the *cessation of the cycle* is the failure of ovulation and hormonal cycling at the brain level, not a primary failure of the endometrial receptors. * **Option C:** Testosterone exerts **negative feedback**, not positive feedback, on the pituitary. It inhibits, rather than stimulates, the secretion of gonadotropins. **3. NEET-PG High-Yield Pearls:** * **Female Athlete Triad:** Consists of low energy availability (with or without disordered eating), menstrual dysfunction (amenorrhea), and low bone mineral density (osteoporosis). * **Virilization:** Chronic steroid use in females leads to hirsutism, clitoromegaly, deepening of the voice, and male-pattern baldness. * **Feedback Loop:** Remember that the HPO axis is sensitive to any exogenous sex steroid (estrogens, progestins, or androgens), all of which can cause "pseudomenopause" or amenorrhea via GnRH suppression.

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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