Reproductive Physiology — MCQs
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Which hormone forms the basis for 'Basal Body Temperature' as a method of detecting ovulation?
In utero, at what gestational age does the fetal human ovary gain the capacity to produce oestrogen?
Which of the following is NOT secreted by the placenta?
All the following are true about human chorionic gonadotropin (HCG) except:
Before the onset of puberty, the GnRH neurons are under the inhibitory control of?
Recruitment of follicles to form primordial follicles is done by which hormone?
Milk production is inhibited by which of the following medications?
After ejaculation into the vagina, sperm retains motility for approximately how long?
Testosterone in males is secreted from which of the following cells?
Which of the following could inhibit the initiation of labor?
Reproductive Physiology Indian Medical PG Practice Questions and MCQs
Question 131: Which hormone forms the basis for 'Basal Body Temperature' as a method of detecting ovulation?
- A. Estrogen
- B. Progesterone (Correct Answer)
- C. HCG
- D. Oxytocin
Explanation: **Explanation:** The correct answer is **Progesterone**. **1. Why Progesterone is Correct:** The Basal Body Temperature (BBT) method relies on the **thermogenic effect** of progesterone. During the follicular phase, body temperature remains relatively low. Following ovulation, the **Corpus Luteum** begins secreting high levels of progesterone. Progesterone acts directly on the **hypothalamic thermoregulatory center**, increasing the set-point and causing a rise in body temperature by approximately **0.3°C to 0.5°C (0.5°F to 1.0°F)**. This rise persists throughout the luteal phase and confirms that ovulation has occurred. **2. Why Other Options are Incorrect:** * **Estrogen:** Estrogen actually has a mild "hypothermic" effect. Just before ovulation, a peak in estrogen often causes a slight dip in temperature, but it does not cause the sustained rise required for BBT monitoring. * **HCG (Human Chorionic Gonadotropin):** This hormone is produced by the syncytiotrophoblast after implantation. It is used for pregnancy detection, not for monitoring the ovulatory cycle. * **Oxytocin:** Known for uterine contractions and milk let-down, oxytocin has no significant role in systemic thermoregulation during the menstrual cycle. **3. Clinical Pearls for NEET-PG:** * **Biphasic Pattern:** A normal ovulatory cycle shows a biphasic BBT curve (low before ovulation, high after). A monophasic curve suggests anovulation. * **Timing:** To be accurate, BBT must be measured immediately upon waking, before any physical activity. * **The "Nadir":** The lowest temperature point (nadir) usually occurs just before the progesterone-induced rise, coinciding closely with the LH surge. * **Luteal Phase Defect:** If the temperature rise lasts less than 10 days, it may indicate progesterone deficiency.
Question 132: In utero, at what gestational age does the fetal human ovary gain the capacity to produce oestrogen?
- A. 6 weeks
- B. 8 weeks (Correct Answer)
- C. 10 weeks
- D. 12 weeks
Explanation: **Explanation:** The correct answer is **8 weeks**. The development of the fetal ovary and its steroidogenic capacity is a critical milestone in reproductive physiology. While the morphological differentiation of the ovary occurs around the 7th to 8th week of gestation, the biochemical machinery required for steroidogenesis—specifically the expression of the enzyme **aromatase**—becomes functional at approximately **8 weeks**. At this stage, the fetal ovary can convert androgens (primarily from the fetal adrenal gland) into oestrogens, although it is important to note that fetal ovarian oestrogen is not essential for female phenotypic development (which is the "default" pathway). **Analysis of Options:** * **6 weeks (A):** At this stage, the gonads are still **indifferent**. The primordial germ cells have reached the genital ridge, but sexual differentiation into an ovary or testis has not yet occurred. * **10 weeks (C) & 12 weeks (D):** These are too late. While folliculogenesis (formation of primordial follicles) begins later (around 16 weeks) and peak germ cell count occurs at 20 weeks, the enzymatic capacity for oestrogen production is established much earlier, by the end of the second month. **Clinical Pearls for NEET-PG:** * **Default Pathway:** Female phenotypic development occurs regardless of the presence of fetal ovaries; it is the *absence* of Testosterone and Anti-Müllerian Hormone (AMH) that leads to the development of Müllerian structures. * **Peak Oocytes:** The fetal ovary contains the maximum number of germ cells (~7 million) at **20 weeks** of gestation. * **Meiotic Arrest:** Oocytes enter the first meiotic division in utero but remain arrested in the **prophase of meiosis I (diplotene stage)** until puberty.
Question 133: Which of the following is NOT secreted by the placenta?
- A. Human Placental Lactogen (HPL)
- B. Human Chorionic Gonadotropin (HCG)
- C. Prolactin (Correct Answer)
- D. Progesterone
Explanation: **Explanation:** The placenta acts as a sophisticated transient endocrine organ, but it does not produce all pregnancy-related hormones. **Why Prolactin is the correct answer:** While prolactin levels rise significantly during pregnancy, the hormone is **not** secreted by the placenta. It is primarily secreted by the **lactotrophs of the anterior pituitary gland**. Additionally, the uterine decidua (maternal side) produces prolactin to help regulate amniotic fluid water and electrolytes, but the placental tissue itself does not synthesize it. **Analysis of Incorrect Options:** * **Human Placental Lactogen (HPL):** Also known as Human Chorionic Somatomammotropin (hCS), it is synthesized by the syncytiotrophoblast. It acts as an insulin antagonist, ensuring a steady glucose supply to the fetus. * **Human Chorionic Gonadotropin (HCG):** Produced by the syncytiotrophoblast shortly after implantation. Its primary role is to rescue and maintain the corpus luteum to ensure continued progesterone production in early pregnancy. * **Progesterone:** Initially produced by the corpus luteum, the placenta takes over progesterone production around the 7th–9th week of gestation (the "luteal-placental shift"). It is essential for maintaining uterine quiescence. **NEET-PG High-Yield Pearls:** 1. **The Syncytiotrophoblast** is the functional endocrine unit of the placenta responsible for HCG, HPL, Estrogen, and Progesterone. 2. **HCG Levels:** Peak at approximately **10 weeks** of gestation and then decline. 3. **HPL Levels:** Increase progressively throughout pregnancy, correlating with placental mass. 4. **Estrogen in Pregnancy:** The placenta cannot produce Estriol ($E_3$) alone; it requires precursors (DHEAS) from the **fetal adrenal glands**, making $E_3$ a marker of feto-placental well-being.
Question 134: All the following are true about human chorionic gonadotropin (HCG) except:
- A. It has luteotrophic action.
- B. It acts on the same receptors as luteinizing hormone (LH).
- C. It is secreted by the syncytiotrophoblast. (Correct Answer)
- D. It is a glycoprotein.
Explanation: ### Explanation **Understanding the Question** The question asks for the "Except" statement regarding Human Chorionic Gonadotropin (hCG). In many standardized exams, if an option is a factually correct statement but the question asks for the "incorrect" one, the marking can be confusing. Here, **Option C is a factually correct statement**, meaning it is **not** the "except" (incorrect) statement. However, based on the provided key, we will analyze the properties of hCG to clarify the physiology. **1. Why Option C is factually TRUE (The Physiology of hCG)** hCG is a glycoprotein hormone produced by the **syncytiotrophoblast** cells of the placenta. Its primary role is to maintain the corpus luteum during the first trimester of pregnancy, ensuring the continued secretion of progesterone until the placenta takes over (the luteal-placental shift). **2. Analysis of Other Options** * **Option A (Luteotrophic action):** This is **TRUE**. hCG "rescues" the corpus luteum from involution, acting as a trophic hormone to maintain its function. * **Option B (Acts on LH receptors):** This is **TRUE**. hCG is structurally similar to LH (sharing the same alpha subunit) and binds to the **LH/hCG receptor**. It has a much longer half-life than LH (24 hours vs. 20 minutes). * **Option D (Glycoprotein):** This is **TRUE**. Like LH, FSH, and TSH, hCG is a heterodimeric glycoprotein consisting of an alpha and a beta subunit. **Note on the Answer Key:** All four options provided (A, B, C, and D) are physiologically **correct** statements about hCG. In a standard NEET-PG format, this would likely be a "controversial" or "all are correct" question. If the question intended to find a false statement, an option like "secreted by cytotrophoblast" would be the typical distractor. **3. High-Yield NEET-PG Pearls** * **Structure:** Alpha ($\alpha$) subunit is identical to LH, FSH, and TSH. The **Beta ($\beta$) subunit** is unique and used for pregnancy testing. * **Peak Levels:** hCG levels double every 48 hours in early pregnancy, peaking at **8–10 weeks** of gestation. * **Clinical Use:** Used in infertility treatment to trigger ovulation (mimics the LH surge). * **Tumor Marker:** Elevated in Gestational Trophoblastic Disease (Hydatidiform mole/Choriocarcinoma) and certain germ cell tumors (Dysgerminoma).
Question 135: Before the onset of puberty, the GnRH neurons are under the inhibitory control of?
- A. Glycine
- B. Glutamate
- C. Gamma amino butyric acid (GABA) (Correct Answer)
- D. Beta-endorphin
Explanation: ### Explanation The onset of puberty is governed by the "gonadostat" mechanism, which involves the removal of central inhibition on **Gonadotropin-Releasing Hormone (GnRH) neurons**. **1. Why GABA is the Correct Answer:** During the prepubertal period, the hypothalamic-pituitary-gonadal (HPG) axis is kept dormant primarily through **tonic neural inhibition**. **Gamma-amino butyric acid (GABA)**, the major inhibitory neurotransmitter in the brain, acts on GnRH neurons to suppress their pulsatile release. As puberty approaches, there is a "brake release" phenomenon where GABAergic tone decreases and excitatory inputs (like Kisspeptin and Glutamate) increase, leading to the high-frequency GnRH pulses required for puberty. **2. Analysis of Incorrect Options:** * **Option A (Glycine):** While Glycine is an inhibitory neurotransmitter, it acts primarily in the spinal cord and brainstem, not in the hypothalamic regulation of GnRH. * **Option B (Glutamate):** Glutamate is an **excitatory** neurotransmitter. It stimulates GnRH release and its activity increases *at* the onset of puberty, rather than inhibiting it beforehand. * **Option D (Beta-endorphin):** Endogenous opioids like beta-endorphins do inhibit GnRH (often seen in exercise-induced amenorrhea or stress), but they are not the primary mediators responsible for the prepubertal quiescent state. **3. High-Yield Clinical Pearls for NEET-PG:** * **Kisspeptin:** This is the "master switch" of puberty. It is a potent stimulator of GnRH neurons. Puberty begins when Kisspeptin levels rise, overcoming GABAergic inhibition. * **Precocious Puberty:** Lesions in the hypothalamus (like hamartomas) can disrupt this inhibitory control, leading to early activation of the HPG axis. * **Nocturnal Pulses:** The first sign of impending puberty is the appearance of LH pulses during **sleep**.
Question 136: Recruitment of follicles to form primordial follicles is done by which hormone?
- A. Estrogen
- B. HCG
- C. Follicle stimulating hormone (Correct Answer)
- D. LH
Explanation: ### Explanation **Correct Option: C (Follicle Stimulating Hormone)** The development of ovarian follicles occurs in two distinct phases: the **pre-antral (gonadotropin-independent)** phase and the **antral (gonadotropin-dependent)** phase. While the initial recruitment of primordial follicles into the growing pool is controlled by local intra-ovarian growth factors (like GDF-9 and BMP-15), the **cyclic recruitment** of a cohort of follicles to progress toward the antral stage and eventual ovulation is strictly driven by **Follicle Stimulating Hormone (FSH)**. FSH binds to receptors on granulosa cells, stimulating their proliferation, increasing aromatase activity, and preventing follicular atresia. **Why the other options are incorrect:** * **A. Estrogen:** Estrogen is a product of follicular development (via the aromatization of androgens). While it exerts feedback on the HPO axis and helps in the proliferation of the endometrium, it does not initiate the recruitment of follicles. * **B. HCG:** Human Chorionic Gonadotropin is structurally similar to LH. Its primary role is to maintain the corpus luteum during early pregnancy to ensure progesterone production; it plays no role in the initial recruitment of follicles. * **D. LH:** Luteinizing Hormone is responsible for the final maturation of the dominant follicle, the mid-cycle surge that triggers ovulation, and the maintenance of the corpus luteum. It acts on theca cells to produce androgens but does not recruit the primary cohort. **High-Yield NEET-PG Pearls:** * **Two-Cell, Two-Gonadotropin Theory:** LH acts on **Theca cells** (producing androgens), while FSH acts on **Granulosa cells** (converting androgens to estrogens). * **The "FSH Window":** The transient rise in FSH during the late luteal/early follicular phase is the critical signal for cyclic recruitment. * **Inhibin B:** Produced by granulosa cells under the influence of FSH, it provides negative feedback to the anterior pituitary to lower FSH levels, aiding in the selection of a single dominant follicle.
Question 137: Milk production is inhibited by which of the following medications?
- A. Bromocriptine (Correct Answer)
- B. Ergotamine
- C. Metoclopromide
- D. Estrogen
Explanation: **Explanation:** The correct answer is **A. Bromocriptine**. **Mechanism of Action:** Milk production (lactogenesis) is primarily controlled by **Prolactin**, a hormone secreted by the anterior pituitary. Prolactin secretion is under tonic inhibition by **Dopamine** (also known as Prolactin-Inhibiting Hormone). **Bromocriptine** is a potent **Dopamine (D2) receptor agonist**. By mimicking dopamine, it suppresses the secretion of prolactin from the pituitary gland, thereby effectively inhibiting milk production and secretion. It is clinically used to treat hyperprolactinemia and to suppress lactation when medically indicated. **Analysis of Incorrect Options:** * **B. Ergotamine:** While an ergot alkaloid like bromocriptine, it acts primarily as a vasoconstrictor (used in migraines) and does not have the specific dopaminergic potency required to suppress prolactin significantly. * **C. Metoclopramide:** This is a **Dopamine antagonist**. By blocking dopamine receptors, it removes the natural inhibition on prolactin, leading to *increased* milk production (galactagogue effect). * **D. Estrogen:** While high levels of estrogen during pregnancy inhibit the *action* of prolactin on the breast tissue, estrogen itself does not inhibit the *production* of prolactin. In fact, estrogen can stimulate prolactin-secreting cells. **High-Yield NEET-PG Pearls:** * **Dopamine = Prolactin Inhibiting Factor (PIF).** Any drug that increases dopamine (e.g., Cabergoline, Bromocriptine) decreases prolactin. * **Cabergoline** is currently the preferred drug over Bromocriptine for lactation suppression due to its longer half-life and better side-effect profile. * **TRH (Thyrotropin-Releasing Hormone)** acts as a prolactin-releasing factor; thus, primary hypothyroidism can lead to hyperprolactinemia. * **Suckling reflex** inhibits dopamine release, thereby increasing prolactin and promoting milk production.
Question 138: After ejaculation into the vagina, sperm retains motility for approximately how long?
- A. 24 hours (Correct Answer)
- B. 36 hours
- C. 72 hours
- D. 1 week
Explanation: **Explanation:** The correct answer is **24 hours (Option A)**. **Understanding the Concept:** While sperm can survive in the female reproductive tract (specifically the cervical mucus and fallopian tubes) for 3 to 5 days, their **motility**—the ability to move effectively toward the oocyte—declines much faster. After ejaculation into the acidic environment of the vagina, most sperm lose their motility within **24 to 48 hours**. For the purposes of standard medical examinations like NEET-PG, the physiological window for functional sperm motility is generally cited as 24 hours. It is important to distinguish between *viability* (staying alive) and *motility* (the ability to swim), as the latter is essential for fertilization. **Analysis of Incorrect Options:** * **36 hours (Option B):** While some sperm may remain motile beyond a day, 36 hours is not the standard physiological average used in clinical textbooks for vaginal ejaculation. * **72 hours (Option C):** This represents the upper limit of sperm **viability** (survival) in the fallopian tubes, but by this time, motility is significantly compromised. * **1 week (Option D):** This is physiologically impossible for human sperm; the hostile environment of the female tract and the depletion of sperm energy reserves (ATP) prevent such long-term survival. **High-Yield Clinical Pearls for NEET-PG:** * **Sperm Life Span:** In the female tract, sperm survive ~48–72 hours, but the **Oocyte** remains viable for only **12–24 hours** after ovulation. * **Capacitation:** This is the final maturation process sperm undergo in the female tract (taking ~7 hours) to become fertile; it involves the removal of cholesterol and glycoproteins from the sperm head. * **Velocity:** Sperm move at a rate of approximately 1–4 mm/min. * **Semen pH:** Semen is slightly alkaline (pH 7.2–8.0) to neutralize the acidic vaginal pH (~4.0), protecting sperm motility.
Question 139: Testosterone in males is secreted from which of the following cells?
- A. Leydig cells (Correct Answer)
- B. Sertoli cells
- C. Seminal vesicles
- D. Epididymis
Explanation: **Explanation:** **Correct Answer: A. Leydig cells** The primary source of testosterone in males is the **Leydig cells** (also known as interstitial cells), located in the connective tissue between the seminiferous tubules. This process is regulated by **Luteinizing Hormone (LH)** from the anterior pituitary, which binds to G-protein coupled receptors on Leydig cells to stimulate the conversion of cholesterol to testosterone. **Analysis of Incorrect Options:** * **B. Sertoli cells:** These are "nurturing" cells located within the seminiferous tubules. Their primary functions include supporting spermatogenesis, forming the blood-testis barrier, and secreting **Inhibin B** and **Androgen Binding Protein (ABP)** under the influence of FSH. They do not synthesize testosterone. * **C. Seminal vesicles:** These are accessory glands that contribute about 60-70% of the seminal fluid volume. They secrete fructose (energy for sperm), prostaglandins, and clotting proteins, but not hormones. * **D. Epididymis:** This is the site for sperm maturation and storage. While it is an androgen-dependent organ, it does not produce testosterone. **High-Yield Clinical Pearls for NEET-PG:** * **LH acts on Leydig cells** (Mnemonic: **L**H = **L**eydig). * **FSH acts on Sertoli cells** (Mnemonic: **F**SH = **S**ertoli). * **Intratesticular testosterone** levels are 20–100 times higher than serum levels, which is essential for normal spermatogenesis. This high concentration is maintained by **ABP** (secreted by Sertoli cells). * The rate-limiting step in testosterone synthesis is the conversion of cholesterol to pregnenolone by the enzyme **cytochrome P450scc** (cholesterol side-chain cleavage enzyme).
Question 140: Which of the following could inhibit the initiation of labor?
- A. Administration of an antagonist of the actions of progesterone
- B. Administration of LH
- C. Administration of an antagonist of PGE2 effects (Correct Answer)
- D. Mechanically dilating and stimulating the cervix
Explanation: ### Explanation The initiation and progression of labor (parturition) involve a complex interplay of hormonal and mechanical factors. The correct answer is **C: Administration of an antagonist of PGE2 effects.** **Why Option C is Correct:** Prostaglandins, specifically **PGE2 and PGF2α**, play a critical role in labor. They are potent stimulators of uterine smooth muscle contraction and are essential for **cervical ripening** (softening and thinning). Prostaglandins increase the number of gap junctions between myometrial cells, facilitating coordinated contractions. Therefore, blocking PGE2 receptors or inhibiting prostaglandin synthesis (e.g., using NSAIDs like Indomethacin) effectively inhibits the initiation of labor and is often used clinically as a tocolytic agent. **Analysis of Incorrect Options:** * **Option A:** Progesterone is the "hormone of pregnancy" that maintains uterine quiescence. An **antagonist** (like Mifepristone) would remove this inhibitory effect, thereby **promoting** labor, not inhibiting it. * **Option B:** LH (Luteinizing Hormone) levels are not primary drivers for the initiation of labor. While LH is crucial for ovulation and early corpus luteum maintenance, it has no inhibitory role in late-term parturition. * **Option D:** Mechanical dilation of the cervix triggers the **Ferguson Reflex**. This neuroendocrine reflex stimulates the release of **Oxytocin** from the posterior pituitary, which increases uterine contractions, thus **promoting** labor. **High-Yield NEET-PG Pearls:** * **Ferguson Reflex:** Cervical stretch → Oxytocin release → Uterine contraction (Positive Feedback Loop). * **Progesterone Withdrawal:** A functional decrease in progesterone activity is a key trigger for labor in many species. * **Tocolytics:** Drugs used to delay labor include Beta-2 agonists (Ritodrine, Terbutaline), Calcium channel blockers (Nifedipine), and Prostaglandin inhibitors (Indomethacin).
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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