Reproductive Physiology Practice Questions

Q: Gonadal sex of the fetus is determined by:

Sex-determining region on the 'Y' chromosome. ### Explanation The sexual differentiation of a fetus occurs in a sequential, hierarchical manner: **Genetic Sex → Gonadal Sex → Phenotypic Sex.** **1. Why the correct answer is right:** **Gonadal sex** refers to whether the undifferentiated bipotential gonads develop into testes or ovaries. This is determined by the presence or absence of the **SRY gene (Sex-determining Region on the Y chromosome)**. * If the SRY gene is present (normally on the Y chromosome), it encodes for the **Testis-Determining Factor (TDF)**, which triggers the medulla of the bipotential gonad to differentiate into **testes**. * In the absence of the SRY gene (as in 46,XX), the cortex of the gonad develops into **ovaries**. **2. Why the incorrect options are wrong:** * **Options A & B (Testosterone and AMH):** These hormones are secreted *by* the fetal testes (Leydig and Sertoli cells, respectively) *after* gonadal sex has already been established. They are responsible for determining **Phenotypic Sex** (internal and external genitalia), not gonadal sex. * **Option D (Estrogen):** Female phenotypic development is largely the "default" pathway and does not require the secretion of fetal estrogen for the initial determination of gonadal sex. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Genetic Sex:** Established at fertilization (XX or XY). * **Timing:** Gonadal differentiation begins around the **6th–7th week** of gestation. * **Sertoli Cells:** Secretes **Anti-Müllerian Hormone (AMH)**, which causes regression of Müllerian ducts (paramesonephric ducts). * **Leydig Cells:** Secretes **Testosterone**, which stimulates the development of Wolffian ducts (mesonephric ducts) into the male internal genitalia (Epididymis, Vas deferens, Seminal vesicles). * **Dihydrotestosterone (DHT):** Responsible for the development of male **external** genitalia (penis and scrotum).

Q: Which of the following is considered a marker for epididymal function?

Carnitine. **Explanation:** The correct answer is **Carnitine**. The composition of seminal fluid is derived from various accessory reproductive organs, and specific biochemical markers are used to assess the functional integrity of these glands. **1. Why Carnitine is correct:** L-Carnitine (and Glycerophosphocholine) is actively secreted by the **epididymis**. It plays a crucial role in the maturation of spermatozoa and the acquisition of motility. High concentrations of free carnitine in the semen are a direct indicator of normal epididymal function. A decrease in carnitine levels often suggests an epididymal obstruction or dysfunction. **2. Why other options are incorrect:** * **Fructose (Option A):** This is the primary marker for the **Seminal Vesicles**. It provides the main energy source for sperm motility. Absence of fructose indicates seminal vesicle agenesis or obstruction of the ejaculatory duct. * **Testosterone (Option B):** This is a steroid hormone produced by the **Leydig cells** of the testes. While essential for spermatogenesis, it is not a specific marker for the function of the exocrine ducts (like the epididymis) in semen analysis. * **Acid Phosphatase (Option C):** This is a classic marker for **Prostatic function**. Other prostatic markers include Citric acid, Zinc, and Prostate-Specific Antigen (PSA). **High-Yield Clinical Pearls for NEET-PG:** * **Epididymis:** Markers include Carnitine, Neutral α-glucosidase, and Glycerophosphocholine. * **Seminal Vesicles:** Marker is Fructose (contributes ~60% of total semen volume). * **Prostate:** Markers include Citric acid, Zinc, and Acid Phosphatase (contributes ~20-30% of volume; gives semen its milky appearance). * **Sperm Maturation:** While sperm are produced in the seminiferous tubules, they acquire **motility and fertilizing capacity** only during their passage through the epididymis.

Q: What is the approximate total number of primordial follicles present at birth?

1-2 Million. **Explanation** The correct answer is **1-2 Million (Option D)**. This question tests the understanding of the chronological decline of germ cells in the female reproductive system, a high-yield topic for NEET-PG. **1. Why Option D is Correct:** During fetal development, primordial germ cells migrate to the gonadal ridge and undergo rapid mitosis. The number of germ cells peaks at **6–7 million** by the **20th week of gestation**. Following this peak, a process of programmed cell death (atresia) begins. By the time of **birth**, the total number of primordial follicles is reduced to approximately **1–2 million**. **2. Why Other Options are Incorrect:** * **Options A and B (2,000–40,000):** These numbers are far too low for birth. By the time a girl reaches **menopause**, the count drops below 1,000. * **Option C (1–2 Lakhs):** This range is closer to the number of follicles present at **puberty**. By the onset of menarche, the count has further depleted to approximately **300,000–400,000**. **3. Clinical Pearls & High-Yield Facts:** * **Peak Germ Cells:** 6–7 million (at 20 weeks gestation). * **At Birth:** 1–2 million. * **At Puberty:** 300,000–400,000. * **Total Ovulated:** Only about **400–500** follicles will actually undergo ovulation during a woman's entire reproductive lifespan; the rest undergo atresia. * **Meiotic Arrest:** Primordial follicles are arrested in the **Prophase of Meiosis I (Diplotene stage)** until ovulation begins after puberty. * **Menopause:** Occurs when the follicular pool is exhausted (typically <1,000 follicles remaining).

Q: Males and females show differences in the age of onset of puberty. The difference in the age of onset of puberty amongst males may be explained by:

Increased Inhibin levels. **Explanation:** The timing of puberty is governed by the reactivation of the hypothalamic-pituitary-gonadal (HPG) axis. In males, the onset of puberty is generally later than in females. This delay is primarily attributed to the feedback mechanisms of the pituitary-gonadal axis, specifically involving **Inhibin**. **Why "Increased Inhibin levels" is correct:** Inhibin (specifically Inhibin B in males) is produced by the Sertoli cells of the testes. Its primary physiological role is the **negative feedback inhibition of FSH** (Follicle-Stimulating Hormone) secretion from the anterior pituitary. In the prepubertal period, males maintain higher levels of Inhibin compared to females. This sustained suppression of FSH keeps the HPG axis in a "quiescent" state for a longer duration, thereby delaying the physiological triggers required for the onset of puberty. **Analysis of Incorrect Options:** * **A & B (Activin and Follistatin):** Activin stimulates FSH release, while Follistatin binds and neutralizes Activin. While they play roles in follicular/spermatogenic development, they are not the primary systemic regulators responsible for the gender-based timing difference in pubertal onset. * **D (Easily releasable FSH pool):** Females actually demonstrate a more "easily releasable" or sensitive FSH response to GnRH pulses in early puberty compared to males. A larger FSH pool would theoretically accelerate puberty, not explain the delay seen in males. **High-Yield NEET-PG Pearls:** * **Inhibin B** is the primary marker of spermatogenesis and Sertoli cell function in males. * **Inhibin A** is the dominant form in females (secreted by the corpus luteum). * The first sign of puberty in males is **testicular enlargement** (>4ml volume), driven by FSH-induced growth of seminiferous tubules. * The "gonadostat" theory suggests puberty begins when the hypothalamus becomes *less* sensitive to negative feedback from sex steroids.

Q: Which of the following characterizes the mid-follicular phase of the menstrual cycle?

Increased inhibin. ### Explanation In the **mid-follicular phase** (days 5–10), the selection of the dominant follicle occurs. This phase is characterized by a shift in the hormonal feedback loop from the pituitary to the ovaries. **Why "Increased Inhibin" is correct:** As the follicles grow under the influence of FSH, the granulosa cells begin to secrete increasing amounts of **Inhibin B**. Inhibin B serves a specific physiological role: it provides negative feedback to the anterior pituitary to selectively **decrease FSH secretion**. This ensures that only the most sensitive follicle (the dominant follicle) continues to grow, while others undergo atresia. **Analysis of Incorrect Options:** * **A. Decreased Estrogen:** Incorrect. During the mid-follicular phase, estrogen levels are **rising** steadily as granulosa cells proliferate and aromatize androgens. * **B. Increased FSH:** Incorrect. FSH levels actually **decline** during the mid-to-late follicular phase due to negative feedback from rising estrogen and Inhibin B. * **C. Decreased LH:** Incorrect. LH levels remain relatively stable or show a **slight increase** during this phase, eventually leading to the LH surge. It does not decrease. **NEET-PG High-Yield Pearls:** * **Inhibin B vs. Inhibin A:** Remember **B** for **B**efore ovulation (follicular phase) and **A** for **A**fter ovulation (luteal phase, secreted by the corpus luteum). * **Two-Cell, Two-Gonadotropin Theory:** LH stimulates **Theca cells** to produce androgens; FSH stimulates **Granulosa cells** to convert those androgens into estrogens (aromatization). * **The Switch:** Estrogen exerts negative feedback throughout most of the cycle, but when it exceeds a threshold (>200 pg/mL for ~48 hours), it switches to **positive feedback**, triggering the LH surge.

Q: Physiological amenorrhea is present in all the following situations except:

Post-puberty. **Explanation:** **Physiological amenorrhea** refers to the natural, non-pathological absence of menstruation during specific stages of a woman's life cycle. 1. **Why "Post-puberty" is the correct answer:** Post-puberty marks the onset of **menarche** and the establishment of regular cyclic hormonal changes (the hypothalamic-pituitary-ovarian axis). In a healthy, non-pregnant, non-lactating female of reproductive age, the absence of menstruation is considered **pathological** (Primary or Secondary Amenorrhea), not physiological. Therefore, post-puberty is the state where menstruation is expected to occur. 2. **Analysis of Incorrect Options:** * **Pre-puberty:** Before puberty, the GnRH pulse generator is dormant, and gonadotropin levels (FSH/LH) are too low to stimulate follicular development or endometrial growth. * **Pregnancy:** This is the most common cause of physiological amenorrhea. High levels of **placental hormones (hCG, Estrogen, and Progesterone)** provide negative feedback to the pituitary, inhibiting the cyclic shedding of the endometrium. * **Lactation:** Elevated **Prolactin** levels during breastfeeding inhibit the pulsatile release of GnRH, leading to "Lactational Amenorrhea." This serves as a natural (though not foolproof) contraceptive mechanism. * *Note:* **Menopause** is the fourth major cause of physiological amenorrhea due to the depletion of ovarian follicles. **High-Yield Clinical Pearls for NEET-PG:** * **Lactational Amenorrhea Method (LAM):** Is most effective only if the mother is exclusively breastfeeding, is less than 6 months postpartum, and remains amenorrheic. * **First sign of Puberty:** Thelarche (breast development), followed by Pubarche, and finally Menarche. * **Primary Amenorrhea definition:** Absence of menarche by age 13 (without secondary sexual characteristics) or age 15 (with secondary sexual characteristics).

Q: Which of the following endocrine structures does not produce progesterone?

Endometrium. **Explanation:** The correct answer is **C. Endometrium**. In reproductive physiology, it is crucial to distinguish between structures that *produce* hormones and those that act as *target tissues*. **1. Why Endometrium is the correct answer:** The endometrium is the mucosal lining of the uterus. It does not synthesize progesterone; rather, it is a **target organ** for progesterone. Under the influence of progesterone, the endometrium undergoes "secretory changes" (increased vascularity and glycogen storage) to prepare for implantation. While it produces local factors like prostaglandins, it lacks the steroidogenic enzymes (like 3β-HSD) required to synthesize progesterone. **2. Analysis of incorrect options:** * **Placenta:** After the "luteal-placental shift" (around 7–9 weeks of gestation), the syncytiotrophoblast of the placenta becomes the primary source of progesterone to maintain pregnancy. * **Follicle:** Specifically, the **Corpus Luteum** (formed from the ruptured follicle after ovulation) is the main source of progesterone during the luteal phase of the menstrual cycle. * **Adrenal Cortex:** The adrenal glands produce small amounts of progesterone as an intermediate precursor in the synthesis of cortisol and androgens. **High-Yield NEET-PG Pearls:** * **Luteal-Placental Shift:** Occurs between 7–10 weeks; before this, the Corpus Luteum of pregnancy is essential. * **Progesterone Function:** It is often called the "Hormone of Pregnancy" because it decreases uterine excitability (quiescence). * **Diagnostic Marker:** A serum progesterone level >3 ng/mL is a reliable indicator that ovulation has occurred.

Question 1

Gonadal sex of the fetus is determined by:

Accepted Answer

Sex-determining region on the 'Y' chromosome

Answer

Secretion of testosterone

Answer

Secretion of anti-Müllerian hormone

Answer

Secretion of estrogen

Question 2

Which of the following is considered a marker for epididymal function?

Accepted Answer

Carnitine

Answer

Fructose

Answer

Testosterone

Answer

Acid phosphatase

Question 3

During early pregnancy, which hormone is secreted by trophoblastic cells to maintain the corpus luteum?

Accepted Answer

Human chorionic gonadotropin (hCG)

Answer

Estrogen

Answer

Luteinizing hormone (LH)

Answer

Progesterone

Question 4

What is the approximate total number of primordial follicles present at birth?

Accepted Answer

1-2 Million

Answer

2000-4000

Answer

20,000-40,000

Answer

1-2 lakhs

Question 5

Males and females show differences in the age of onset of puberty. The difference in the age of onset of puberty amongst males may be explained by:

Accepted Answer

Increased Inhibin levels

Answer

Increased Activin-A levels

Answer

Decreased Follistatin levels

Answer

Easily releasable FSH pool

Question 6

Which of the following statements is FALSE regarding hormonal variations during a normal menstrual cycle?

Accepted Answer

FSH secretion is inhibited by estrogen secreted from the growing follicle but stimulated by inhibin B

Answer

Estrogen inhibits FSH release and stimulates LH release

Answer

LH shows a biphasic response during the follicular phase

Answer

FSH induces the formation of LH receptors on granulosa cells

Question 7

Which of the following characterizes the mid-follicular phase of the menstrual cycle?

Accepted Answer

Increased inhibin

Answer

Decreased estrogen

Answer

Increased FSH

Answer

Decreased LH

Question 8

Physiological amenorrhea is present in all the following situations except:

Accepted Answer

Post-puberty

Answer

Pregnancy

Answer

Lactation

Answer

Pre-puberty

Question 9

The enzyme 5a-reductase mediated conversion of testosterone to dihydrotestosterone is NOT required for which of the following actions?

Accepted Answer

Spermatogenesis

Answer

Formation of male external genitalia in the fetus

Answer

Prostatic hypertrophy in elderly males

Answer

Pubertal changes in the male adolescent

Question 10

Which of the following endocrine structures does not produce progesterone?

Accepted Answer

Endometrium

Answer

Placenta

Answer

Follicle

Answer

Adrenal cortex

Reproductive Physiology — MCQs

Reproductive Physiology — MCQs

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