Reproductive Physiology Practice Questions

Q: In the physiology of the menstrual cycle, all of the following statements are true EXCEPT?

The follicular phase is constant in length.. **Explanation:** The menstrual cycle is divided into the follicular (proliferative) and luteal (secretory) phases. Understanding the variability of these phases is a high-yield concept for NEET-PG. **1. Why Option B is the Correct Answer (The False Statement):** The **luteal phase is constant** in length, typically lasting 14 days (range 13–15 days) due to the fixed lifespan of the corpus luteum. In contrast, the **follicular phase is highly variable**. Variations in total cycle length (e.g., a 28-day vs. 35-day cycle) are almost entirely due to differences in the duration of the follicular phase. **2. Analysis of Other Options:** * **Option A:** Ovulation is triggered by the LH surge. It occurs approximately **32–36 hours after the onset** of the surge and 10–12 hours after the LH peak. * **Option C:** Menstruation is a "withdrawal bleed." When fertilization fails, the corpus luteum involutes, leading to a sharp drop in progesterone. This causes spiral artery vasospasm, tissue ischemia, and endometrial shedding. * **Option D:** A normal menstrual cycle ranges from **21 to 35 days** (average 28 days). Cycles outside this range are classified as polymenorrhea ( 35 days). **Clinical Pearls for NEET-PG:** * **LH Surge Trigger:** Caused by a positive feedback effect of Estrogen (levels >200 pg/mL for >48 hours). * **Mittelschmerz:** Mid-cycle pelvic pain associated with ovulation. * **Progesterone:** The "hormone of pregnancy," responsible for the secretory changes in the endometrium and the rise in basal body temperature (0.5°F) post-ovulation.

Q: The first polar body is formed after which of the following events?

First meiosis. **Explanation:** The formation of the first polar body is a hallmark of the completion of **Meiosis I** during oogenesis. 1. **Why the correct answer is right:** In the female fetus, primary oocytes begin Meiosis I but are arrested in the **prophase (diplotene stage)** until puberty. Following the LH surge during each menstrual cycle, the primary oocyte (diploid, 2n) completes its first meiotic division just before ovulation. This division is **asymmetric cytokinesis**, resulting in one large **secondary oocyte** (haploid, n) and one small, non-functional **first polar body**. The polar body contains the discarded set of homologous chromosomes. 2. **Why other options are wrong:** * **Mitosis:** This occurs only during the fetal period when oogonia proliferate to form primary oocytes. It does not involve reduction division or polar body formation. * **Second meiosis:** Completion of Meiosis II occurs only **after fertilization**. This division results in the formation of the **second polar body** and the mature zygote. * **Fertilization:** This is the trigger for the completion of Meiosis II, not Meiosis I. **High-Yield Clinical Pearls for NEET-PG:** * **Arrest Points:** Remember "Meiosis I is arrested in **Prophase** (Dictyate/Diplotene) until puberty; Meiosis II is arrested in **Metaphase** until fertilization." (Mnemonic: **M**etaphase = **M**eet the sperm). * **Chromosome Status:** The first polar body is haploid (n) but contains double-structured chromosomes (2 chromatids each). * **Clinical Significance:** In IVF (In-Vitro Fertilization), the presence of the first polar body is used as a marker of **oocyte maturity** (MII stage).

Q: What is the approximate time taken for the development of spermatozoa from spermatogonium?

70-75 days. **Explanation:** The process of **spermatogenesis**—the transformation of primitive germ cells (spermatogonia) into mature spermatozoa—is a highly regulated and lengthy process occurring within the seminiferous tubules. **1. Why Option D is Correct:** In humans, the total duration of spermatogenesis is approximately **74 days** (commonly cited as **70–75 days** in standard textbooks like Guyton and Ganong). This timeline includes: * **Spermatocytogenesis:** Mitotic division of spermatogonia to form primary spermatocytes. * **Meiosis:** Primary spermatocytes undergo two meiotic divisions to form haploid spermatids. * **Spermiogenesis:** The morphological transformation of rounded spermatids into elongated, motile spermatozoa (taking about 21–24 days of the total cycle). **2. Why Other Options are Incorrect:** * **Options A, B, and C (30–55 days):** These timeframes are too short for the human biological cycle. While the duration varies across species (e.g., ~35 days in mice), in humans, any disruption (like high fever or toxins) takes nearly 2.5 months to manifest as a change in the sperm count of the ejaculate due to this fixed 74-day cycle. **3. NEET-PG High-Yield Pearls:** * **Spermiogenesis vs. Spermatogenesis:** Do not confuse the two. *Spermiogenesis* is specifically the maturation of spermatids to sperm (no cell division). * **Spermiation:** The process by which mature spermatozoa are released from Sertoli cells into the lumen of seminiferous tubules. * **Storage:** After production, sperm move to the **epididymis** for functional maturation and storage, which takes an additional 12–14 days. * **Hormonal Control:** LH stimulates Leydig cells (Testosterone), while FSH stimulates Sertoli cells to support spermatogenesis.

Q: Which one of the following substances is the most potent androgen?

Dihydrotestosterone. **Explanation:** The potency of an androgen is determined by its affinity for the androgen receptor (AR) and its ability to initiate gene transcription. **Why Dihydrotestosterone (DHT) is the correct answer:** DHT is the most potent naturally occurring androgen [1]. It is synthesized from testosterone by the enzyme **5Ͱ-reductase** in peripheral tissues (like the prostate and skin). DHT has a **2-3 times higher affinity** for the androgen receptor than testosterone and dissociates from the receptor much more slowly. This makes its biological effect significantly more powerful, especially in the development of male external genitalia and prostate growth [3]. **Analysis of Incorrect Options:** * **Testosterone (Option D):** While it is the primary circulating androgen produced by Leydig cells [2], it acts as a "pro-hormone" for DHT in many tissues. It is less potent than DHT but more potent than the adrenal androgens. * **Androstenedione (Option C):** This is a weak androgen produced by the adrenal cortex and testes [1]. It serves primarily as a precursor for the synthesis of testosterone and estrogens. * **Dehydroepiandrosterone (DHEA) (Option A):** (Note: The option lists "Dihydroepiandrostendione," likely referring to DHEA). DHEA is a very weak adrenal androgen with low affinity for the androgen receptor. It must be converted to testosterone or DHT to exert significant androgenic effects. **NEET-PG High-Yield Pearls:** * **Potency Order:** DHT > Testosterone > Androstenedione > DHEA. * **Enzyme Fact:** 5Ͱ-reductase inhibitors (e.g., **Finasteride**) are used clinically to treat BPH and male pattern baldness by blocking the conversion of testosterone to the more potent DHT. * **Clinical Correlation:** In **5Ͱ-reductase deficiency**, individuals have normal internal male structures (testosterone-dependent) but ambiguous or female-looking external genitalia at birth (DHT-dependent) [3].

Q: Human Chorionic Gonadotropin (HCG) is secreted from which of the following?

Placenta. **Explanation:** **Correct Answer: A. Placenta** Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone produced by the **syncytiotrophoblast cells** of the placenta. Its primary physiological role is to maintain the **corpus luteum** during the first trimester of pregnancy, ensuring the continued secretion of progesterone until the placenta takes over steroidogenesis (the luteal-placental shift). This prevents the onset of menstruation and sustains the endometrial lining for the developing embryo. **Why incorrect options are wrong:** * **B. Pancreas:** The pancreas is an endocrine and exocrine gland responsible for secreting insulin, glucagon, somatostatin, and digestive enzymes. It has no role in hCG production. * **C. Lung:** While certain lung pathologies (like small cell carcinoma) can produce hormones ectopically (e.g., ACTH or ADH), the lung is not a physiological source of hCG. * **D. Liver:** The liver is responsible for protein synthesis, detoxification, and bile production. It does not secrete gonadotropins. **High-Yield Clinical Pearls for NEET-PG:** * **Structure:** hCG is a dimer consisting of an **alpha (α) subunit** (identical to LH, FSH, and TSH) and a **beta (β) subunit** (unique to hCG, providing biological specificity). * **Detection:** It can be detected in maternal blood as early as **6–8 days after conception** and in urine by **10–12 days**. * **Peak Levels:** hCG levels double every 48 hours in early pregnancy, reaching a peak at approximately **8–10 weeks** of gestation before declining. * **Clinical Marker:** Abnormally high levels are seen in **molar pregnancies** and **choriocarcinoma**, while low levels for gestational age may indicate an ectopic pregnancy or impending miscarriage.

Q: Which hormone reaches its peak level during the luteal phase of the menstrual cycle?

Progesterone. **Explanation:** The menstrual cycle is divided into the follicular phase, ovulation, and the luteal phase. The **luteal phase** (Days 15–28) is characterized by the transformation of the ruptured follicle into the **corpus luteum** under the influence of LH. **Why Progesterone is Correct:** The primary function of the corpus luteum is to secrete large quantities of **progesterone**. Progesterone levels rise significantly during the mid-luteal phase (peaking around day 21) to prepare the endometrium for implantation by increasing its vascularity and secretory activity. Therefore, progesterone is the dominant hormone of the luteal phase. **Why Other Options are Incorrect:** * **LH (Luteinizing Hormone):** LH reaches its absolute peak approximately 10–12 hours **before ovulation** (the LH surge). During the luteal phase, LH levels actually decline due to negative feedback from high progesterone levels. * **FSH (Follicle-Stimulating Hormone):** FSH peaks during the early follicular phase (to recruit follicles) and again during the pre-ovulatory surge. It remains low during the luteal phase. * **Estrogen:** While estrogen has a second, smaller peak during the mid-luteal phase, its **primary and highest peak** occurs just before ovulation (late follicular phase) to trigger the LH surge. **NEET-PG High-Yield Pearls:** 1. **Fixed Duration:** The luteal phase is constant at **14 days**, whereas the follicular phase varies in length. 2. **Thermogenic Effect:** Progesterone causes a 0.5°F rise in basal body temperature after ovulation, a clinical marker used to track the luteal phase. 3. **Luteal-Placental Shift:** If pregnancy occurs, the corpus luteum maintains progesterone production for 8–10 weeks until the placenta takes over.

Q: In men, luteinizing hormone (LH) primarily controls the secretion of which hormone?

Testosterone. ### Explanation The hypothalamic-pituitary-gonadal (HPG) axis regulates male reproductive function through two primary gonadotropins: **Luteinizing Hormone (LH)** and **Follicle-Stimulating Hormone (FSH)**. **Why Testosterone is Correct:** LH acts specifically on the **Leydig cells** (interstitial cells) located in the connective tissue between seminiferous tubules. LH binds to G-protein coupled receptors on these cells, stimulating the conversion of cholesterol to pregnenolone via the enzyme *cholesterol desmolase*. This is the rate-limiting step in the synthesis of **Testosterone**. Therefore, LH is the primary trophic hormone for testosterone production. **Why Other Options are Incorrect:** * **Inhibin:** This is secreted by **Sertoli cells** in response to **FSH** and high sperm counts. It provides negative feedback specifically to the anterior pituitary to inhibit FSH secretion. * **Anti-Müllerian Hormone (AMH):** Produced by fetal Sertoli cells to cause regression of Müllerian ducts. In adults, it is a marker of Sertoli cell function but is not primarily regulated by LH. * **Androgen-binding protein (ABP):** This is synthesized by **Sertoli cells** under the influence of **FSH**. ABP helps maintain high local concentrations of testosterone within the seminiferous tubules, which is essential for spermiogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** **L**H acts on **L**eydig cells; **S**ertoli cells are stimulated by **F**SH (to support **S**permatogenesis). * **Negative Feedback:** Testosterone inhibits both the Hypothalamus (GnRH) and the Anterior Pituitary (LH), whereas Inhibin only inhibits the Anterior Pituitary (FSH). * **Blood-Testis Barrier:** Formed by tight junctions between Sertoli cells, protecting developing germ cells from the immune system.

Q: What is considered the normal sperm count per milliliter?

90-110 million/ml. ### Explanation **1. Understanding the Correct Answer (Option D: 90-110 million/ml)** In classical physiology (based on Guyton and Hall), the average concentration of sperm in semen is approximately **100 million per milliliter**, with a typical range of **80 to 120 million/ml**. Therefore, **90-110 million/ml** represents the physiological "normal" baseline for a healthy male. While modern fertility standards have lowered the threshold for clinical "adequacy," standard physiological textbooks used for NEET-PG preparation still emphasize this higher range as the biological norm. **2. Analysis of Incorrect Options** * **Options A, B, and C (20-80 million/ml):** While these values are frequently encountered in clinical practice and may still result in successful fertilization, they are considered below the physiological average. Specifically, a count below **20 million/ml** is clinically defined as **Oligozoospermia**, which significantly increases the risk of infertility. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **WHO 2021 Criteria:** For clinical diagnosis, the WHO defines the lower reference limit for sperm concentration as **15 million/ml** (or 39 million per total ejaculate). Do not confuse this "minimum clinical limit" with the "physiological normal" of 100 million/ml. * **Volume:** Normal ejaculate volume is **2 to 5 ml**. * **Sterility Threshold:** A person is generally considered functionally sterile when the sperm count falls below **20 million/ml**. * **Morphology & Motility:** For normal fertility, at least **40%** of sperm should be motile and at least **4%** (Kruger’s criteria) should have normal morphology. * **Spermatogenesis Duration:** The entire process of spermatogenesis takes approximately **74 days**.

Question 1

Which clotting factor decreases during pregnancy?

Accepted Answer

Fibrinogen

Answer

Factor XIII

Answer

Factor VIII

Answer

Factor X

Question 2

In the physiology of the menstrual cycle, all of the following statements are true EXCEPT?

Accepted Answer

The follicular phase is constant in length.

Answer

Ovulation follows 36 hours after the onset of the LH surge.

Answer

Withdrawal of endogenous progesterone results in endometrial breakdown and subsequent menstruation.

Answer

The average cycle length is 21-35 days.

Question 3

The first polar body is formed after which of the following events?

Accepted Answer

First meiosis

Answer

Mitosis

Answer

Second meiosis

Answer

Fertilization

Question 4

What is the approximate time taken for the development of spermatozoa from spermatogonium?

Accepted Answer

70-75 days

Answer

30-35 days

Answer

40-45 days

Answer

50-55 days

Question 5

Which one of the following substances is the most potent androgen?

Accepted Answer

Dihydrotestosterone

Answer

Dihydroepiandrostendione

Answer

Androstendione

Answer

Testosterone

Question 6

Which of the following statements accurately describes the hormonal changes during a normal menstrual cycle?

Accepted Answer

Progesterone levels are highest during the secretory phase.

Answer

LH levels are lowest in the mid-cycle.

Answer

FSH levels are highest during the luteal phase.

Answer

Estradiol levels are highest during the mid-cycle.

Question 7

Human Chorionic Gonadotropin (HCG) is secreted from which of the following?

Accepted Answer

Placenta

Answer

Pancreas

Answer

Lung

Answer

Liver

Question 8

Which hormone reaches its peak level during the luteal phase of the menstrual cycle?

Accepted Answer

Progesterone

Answer

Luteinizing Hormone (LH)

Answer

Follicle-Stimulating Hormone (FSH)

Answer

Estrogen

Question 9

In men, luteinizing hormone (LH) primarily controls the secretion of which hormone?

Accepted Answer

Testosterone

Answer

Inhibin

Answer

Anti-Müllerian hormone (AMH)

Answer

Androgen-binding protein (ABP)

Question 10

What is considered the normal sperm count per milliliter?

Accepted Answer

90-110 million/ml

Answer

20-40 million/ml

Answer

40-60 million/ml

Answer

60-80 million/ml

Reproductive Physiology — MCQs

Reproductive Physiology — MCQs

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