Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 281: What is the effect of a higher pulse frequency of Gonadotropin-Releasing Hormone (GnRH)?

A. Stimulates FSH preferentially
B. Stimulates LH preferentially (Correct Answer)
C. Decreases both FSH and LH
D. Decreases LH preferentially

Explanation: **Explanation:** The secretion of Gonadotropins (LH and FSH) from the anterior pituitary is governed by the **pulsatile release** of GnRH from the hypothalamus. The pituitary gland decodes the frequency and amplitude of these pulses to determine which hormone to secrete. **1. Why Option B is correct:** A **high-frequency** (fast) pulse of GnRH (e.g., one pulse every 60–90 minutes) favors the expression of the LH $\beta$-subunit gene, leading to the **preferential secretion of Luteinizing Hormone (LH)**. This is physiologically evident during the late follicular phase of the menstrual cycle, where increased GnRH pulse frequency contributes to the LH surge required for ovulation. **2. Why other options are incorrect:** * **Option A:** **Low-frequency** (slow) pulses of GnRH (e.g., one pulse every 120–180 minutes) preferentially stimulate the secretion of **Follicle-Stimulating Hormone (FSH)**. This occurs typically during the early follicular phase. * **Option C & D:** While GnRH is generally stimulatory, a **continuous (non-pulsatile)** infusion of GnRH leads to the downregulation (internalization) of GnRH receptors on gonadotropes. This results in a profound decrease in both LH and FSH, a process known as medical castration. **High-Yield Clinical Pearls for NEET-PG:** * **GnRH Agonists (e.g., Leuprolide):** Used in a **continuous** fashion to treat precocious puberty, prostate cancer, and endometriosis by suppressing the pituitary-gonadal axis. * **Kallmann Syndrome:** Characterized by delayed puberty and anosmia due to the failure of GnRH neurons to migrate from the olfactory placode to the hypothalamus. * **Pulse Generator:** Located in the **Arcuate nucleus** of the hypothalamus.

Question 282: All of the following are true about fetal circulation EXCEPT?

A. Pulmonary vascular resistance is low (Correct Answer)
B. Umbilical arteries carry deoxygenated blood
C. Lungs are collapsed and filled with fluid
D. Source of oxygen in fetal circulation is the placenta

Explanation: **Explanation:** In fetal circulation, the lungs are non-functional for gas exchange. Consequently, the **pulmonary vascular resistance (PVR) is extremely high** due to hypoxic pulmonary vasoconstriction and the physical compression of vessels by fluid-filled alveoli. This high resistance shunts the majority of right ventricular output away from the lungs through the **ductus arteriosus** into the systemic circulation. Therefore, Option A is the false statement. **Analysis of other options:** * **Option B:** True. The two umbilical arteries carry deoxygenated, nutrient-poor blood from the fetus back to the placenta. * **Option C:** True. In utero, the lungs are collapsed (non-expanded) and the potential air spaces are filled with fetal lung fluid, not air. * **Option D:** True. The placenta serves as the organ of respiration for the fetus, where gas exchange occurs between maternal and fetal blood. **High-Yield NEET-PG Pearls:** 1. **Oxygen Saturation:** The highest $PO_2$ in fetal circulation is found in the **umbilical vein** (approx. 80% saturation), which carries oxygenated blood from the placenta to the fetus. 2. **First Breath Changes:** At birth, lung expansion and increased $O_2$ levels cause a dramatic **drop in PVR** and a rise in systemic vascular resistance (due to loss of low-resistance placental circuit). 3. **Shunts:** There are three anatomical shunts in fetal life: **Ductus venosus** (bypasses liver), **Foramen ovale** (bypasses lungs, RA to LA), and **Ductus arteriosus** (bypasses lungs, Pulmonary Artery to Aorta).

Question 283: The placenta secretes a hormone that participates in the stimulation of ductal growth in the mammary gland during pregnancy. Which hormone is this?

A. Endothelial growth factor (EGF)
B. Human chorionic gonadotropin (HCG)
C. Human chorionic somatotropin (HCS) (Correct Answer)
D. Relaxin

Explanation: ### Explanation **Correct Option: C. Human chorionic somatotropin (HCS)** **Mechanism:** Human chorionic somatotropin (HCS), also known as **Human Placental Lactogen (hPL)**, is a protein hormone secreted by the syncytiotrophoblast of the placenta starting around the 5th week of pregnancy. It is structurally similar to growth hormone and prolactin. Its primary functions are: 1. **Metabolic:** It acts as a "maternal diabetogenic" hormone by decreasing maternal insulin sensitivity, ensuring a steady supply of glucose to the fetus. 2. **Mammary Development:** Along with estrogen and progesterone, HCS plays a crucial role in stimulating the **growth of ducts and development of alveoli** in the mammary glands to prepare for lactation. **Why other options are incorrect:** * **A. Endothelial growth factor (EGF):** While growth factors are involved in general cellular proliferation, EGF is not a primary placental hormone responsible for mammary ductal morphogenesis during pregnancy. * **B. Human chorionic gonadotropin (HCG):** Its primary role is to maintain the corpus luteum during early pregnancy to ensure continued progesterone production. It does not have a direct effect on mammary ductal growth. * **D. Relaxin:** Secreted by the corpus luteum and placenta, its main role is to soften the cervix and relax the pelvic ligaments (symphysis pubis) to facilitate delivery. **High-Yield NEET-PG Pearls:** * **HCS/hPL** is the hormone produced in the largest amount by the placenta. * Its levels are directly proportional to **placental mass**; therefore, low levels may indicate placental insufficiency. * **Mammary Growth Summary:** Estrogen stimulates **ductal** growth; Progesterone stimulates **lobulo-alveolar** development; HCS/hPL supports both. * HCS is a potent **lipolytic** agent, increasing free fatty acids in maternal blood as an alternative energy source for the mother.

Question 284: Which of the following is seen in the ovulatory phase?

A. Stimulation of continuation of reduction division of oocytes (Correct Answer)
B. Inhibin A is increased
C. FSH increases steroid synthesis in granulosa cells
D. Activin causes FSH to act on granulosa cells

Explanation: ### Explanation **1. Why Option A is Correct:** The ovulatory phase is triggered by the **LH surge**. One of the most critical functions of the LH surge is the **resumption of meiosis I** in the primary oocyte. Since birth, primary oocytes are arrested in the prophase of meiosis I (specifically the diplotene stage). The LH surge stimulates the continuation of this reduction division, leading to the completion of meiosis I and the formation of the **secondary oocyte** and the first polar body just before ovulation. **2. Why the Other Options are Incorrect:** * **Option B:** **Inhibin B** is the dominant inhibin during the follicular and ovulatory phases (secreted by granulosa cells). **Inhibin A** levels only rise significantly during the **luteal phase**, as it is secreted by the corpus luteum. * **Option C:** While FSH does stimulate granulosa cells, this occurs primarily during the **follicular phase** to promote follicular growth and aromatase activity. During the ovulatory phase, the LH surge takes over the primary role of driving terminal maturation and steroidogenesis. * **Option D:** Activin does enhance FSH secretion and FSH-induced LH receptor expression, but this is a regulatory mechanism occurring during the **early follicular phase** to select the dominant follicle, not the defining event of the ovulatory phase. **3. High-Yield NEET-PG Pearls:** * **Meiotic Arrest:** Oocytes are arrested in **Prophase I (Diplotene)** from birth until puberty/ovulation. * **Second Arrest:** After the LH surge, meiosis II begins but arrests in **Metaphase II**. It is only completed if fertilization occurs. * **The LH Surge:** Occurs 24–36 hours before ovulation. It is the reliable predictor of ovulation used in urinary kits. * **Stigma:** The small area on the ovarian surface that thins and ruptures to release the oocyte during the ovulatory phase.

Question 285: Where does spermatozoa attain maturity during its passage?

A. Seminal vesicles
B. Epididymis (Correct Answer)
C. Testes
D. Prostate

Explanation: **Explanation:** The correct answer is **B. Epididymis**. **1. Why Epididymis is correct:** While spermatogenesis (the production of sperm) occurs in the seminiferous tubules of the **testes**, the resulting spermatozoa are initially immotile and incapable of fertilizing an ovum. As they pass through the **epididymis** (specifically over a period of 12–26 days), they undergo **physiological maturation**. During this transit, they acquire forward progressive motility, undergo changes in the plasma membrane (addition of glycoproteins), and develop the ability to bind to the zona pellucida. **2. Why other options are incorrect:** * **A. Seminal vesicles:** These are accessory glands that secrete a thick, fructose-rich fluid (providing energy for sperm) and prostaglandins. They contribute about 60-70% of the total semen volume but do not play a role in the maturation process. * **C. Testes:** The testes are the site of sperm *production* (spermatogenesis), but the sperm leaving the testes are morphologically complete yet functionally immature. * **D. Prostate:** The prostate gland secretes a thin, alkaline fluid that helps neutralize the acidity of the vaginal tract and contains enzymes like PSA (Prostate-Specific Antigen) for semen liquefaction. It does not involve sperm maturation. **High-Yield NEET-PG Pearls:** * **Capacitation:** Do not confuse maturation with *capacitation*. Maturation occurs in the **epididymis**, whereas capacitation (the final activation step) occurs in the **female reproductive tract**. * **Storage:** The epididymis is also the primary site for sperm storage; sperm can remain viable here for several weeks. * **Blood-Testis Barrier:** Formed by **Sertoli cells** (Tight junctions), protecting developing germ cells from the immune system. * **Spermiogenesis:** The transformation of circular spermatids into elongated spermatozoa (occurs in the testes).

Question 286: Maximum prostaglandin concentration is seen in which body fluid?

A. Seminal fluid (Correct Answer)
B. Amniotic fluid
C. Tear
D. Saliva

Explanation: **Explanation:** The correct answer is **Seminal fluid**. **1. Why Seminal Fluid is Correct:** Seminal fluid contains the highest concentration of prostaglandins in the human body (approximately 100–300 µg/mL). These are primarily secreted by the **seminal vesicles**. Prostaglandins (specifically PGE and PGF series) play a crucial role in male fertility by: * Reacting with female cervical mucus to make it more receptive to sperm penetration. * Stimulating reverse peristaltic contractions in the uterus and fallopian tubes to facilitate sperm transport toward the ovum. **2. Why Other Options are Incorrect:** * **Amniotic fluid:** While prostaglandins are present here and increase significantly during labor (to help with cervical ripening and uterine contractions), the concentration remains much lower than that found in semen. * **Tears and Saliva:** These fluids contain only trace amounts of prostaglandins, primarily acting as local inflammatory mediators or protective factors, but they are not major storage or secretory sites. **3. High-Yield Clinical Pearls for NEET-PG:** * **Source:** 60% of semen volume comes from seminal vesicles, which provide fructose (energy) and prostaglandins. * **Clinical Significance:** Low prostaglandin levels in semen are associated with certain types of male infertility. * **Prostaglandin Synthesis:** They are derived from **arachidonic acid** via the cyclooxygenase (COX) pathway. * **Uterine Effect:** Seminal prostaglandins cause the female reproductive tract to contract "upwards," aiding sperm motility—a process often tested in reproductive physiology.

Question 287: What is the enzyme associated with the conversion of androgen to oestrogen in the growing ovarian follicle?

A. Desmolase
B. Isomerase
C. Aromatase (Correct Answer)
D. Hydroxylase

Explanation: ### Explanation The conversion of androgens to estrogens is a critical step in the ovarian cycle, governed by the **Two-Cell, Two-Gonadotropin Theory**. **1. Why Aromatase is Correct:** In the growing ovarian follicle, **LH** stimulates **Theca cells** to produce androgens (androstenedione and testosterone) from cholesterol. These androgens then diffuse across the basement membrane into the **Granulosa cells**. Under the influence of **FSH**, the enzyme **Aromatase** (a member of the Cytochrome P450 superfamily, CYP19A1) catalyzes the "aromatization" of the A-ring of these androgens to produce estrogens (estrone and estradiol). **2. Analysis of Incorrect Options:** * **Desmolase (Cholesterol Side-Chain Cleavage Enzyme):** This enzyme converts Cholesterol to Pregnenolone. It is the rate-limiting step in overall steroidogenesis but does not perform the final conversion to estrogen. * **Isomerase (3β-Hydroxysteroid Dehydrogenase/Δ5-4 Isomerase):** This enzyme converts Pregnenolone to Progesterone. It is involved in the early stages of the steroid pathway. * **Hydroxylase:** Enzymes like 17α-hydroxylase or 21-hydroxylase are involved in adding hydroxyl groups at specific positions to create precursors for cortisol or androgens, but they do not synthesize the aromatic ring characteristic of estrogens. **3. NEET-PG High-Yield Pearls:** * **Rate-limiting step of Oogenesis:** Cholesterol to Pregnenolone (via Desmolase). * **Aromatase Inhibitors:** Drugs like Letrozole and Anastrozole are used clinically in breast cancer treatment and ovulation induction. * **FSH vs. LH:** Remember: **L**H acts on **T**heca cells (to make androgens); **F**SH acts on **G**ranulosa cells (to stimulate aromatase). * **Estrogen Potency:** Estradiol (E2) > Estrone (E1) > Estriol (E3). Estradiol is the primary estrogen produced by the growing follicle.

Question 288: Which hormone is secreted by Sertoli cells?

A. Testosterone
B. Inhibin (Correct Answer)
C. Luteinizing hormone (LH)
D. Follicle-stimulating hormone (FSH)

Explanation: **Explanation:** The correct answer is **Inhibin**. Sertoli cells, often called "nurse cells," are located within the seminiferous tubules and play a vital role in spermatogenesis. They secrete **Inhibin B**, which provides negative feedback to the anterior pituitary to specifically inhibit the secretion of Follicle-Stimulating Hormone (FSH). **Analysis of Options:** * **Inhibin (Correct):** Secreted by Sertoli cells in response to FSH stimulation. It regulates the pituitary-testicular axis by suppressing FSH without affecting LH. * **Testosterone (Incorrect):** This is secreted by the **Leydig cells** (interstitial cells) located outside the seminiferous tubules, primarily under the influence of LH. * **Luteinizing Hormone (LH) & Follicle-Stimulating Hormone (FSH) (Incorrect):** These are gonadotropins secreted by the **gonadotrophs of the anterior pituitary gland**, not the testes. **High-Yield Clinical Pearls for NEET-PG:** * **Blood-Testis Barrier:** Formed by tight junctions between adjacent Sertoli cells; it protects developing germ cells from the immune system. * **Other Sertoli Secretions:** Besides Inhibin, they secrete **Androgen Binding Protein (ABP)** (to maintain high local testosterone), **Anti-Müllerian Hormone (AMH)** (during fetal life), and **Estrogen** (via aromatization of testosterone). * **Mnemonic:** **S**ertoli cells = **S**upport sperm, **S**ecrete Inhibin, and are stimulated by F**S**H. **L**eydig cells = **L**ipid-rich, secrete Testosterone, and are stimulated by **L**H.

Question 289: What is the normal sperm count?

A. 60-100 lakh/mm3
B. 4-5 million/mm3
C. 60-120 lakh/mm3
D. 60-120 million/mL (Correct Answer)

Explanation: ### Explanation **1. Understanding the Correct Answer (Option D)** The normal sperm count in a healthy adult male typically ranges from **60 to 120 million per milliliter (mL)** of semen. According to standard physiological texts (like Guyton and Ganong), a count below 20 million/mL is generally associated with infertility (oligozoospermia). It is crucial to note the units: sperm density is measured per **mL of ejaculate**, not per cubic millimeter (mm³). **2. Analysis of Incorrect Options** * **Options A & C (Lakh/mm³):** These options use "lakh" (a common Indian unit) and "mm³." While 60–120 lakh equals 6–12 million, the volume unit **mm³** is incorrect for semen analysis. One mL is equal to 1,000 mm³; therefore, a count in mm³ would be numerically much smaller. * **Option B (4-5 million/mm³):** This is a "distractor" value. 4.5 to 5.5 million/mm³ is the normal range for **Red Blood Cell (RBC) count** in adult males. Students often confuse these two physiological constants during the exam. **3. High-Yield Clinical Pearls for NEET-PG** * **WHO 2021 Criteria (6th Ed):** While physiological ranges are broad, the WHO lower reference limit for sperm concentration is **15 million/mL**. * **Terminology:** * **Oligozoospermia:** <15-20 million/mL. * **Azoospermia:** Total absence of sperm in ejaculate. * **Aspermia:** Absence of ejaculate volume. * **Asthenozoospermia:** Reduced sperm motility. * **Teratozoospermia:** Abnormal sperm morphology. * **Volume:** Normal ejaculate volume is **1.5 to 5 mL**. * **pH:** Semen is slightly alkaline (**7.2–8.0**), which helps neutralize the acidic vaginal environment.

Question 290: What is the normal duration of menstrual flow?

A. 2-7 days (Correct Answer)
B. 7-10 days
C. 2 days
D. 5-9 days

Explanation: The menstrual cycle is a complex physiological process governed by the hypothalamic-pituitary-ovarian axis. The **menstrual phase** (menses) represents the shedding of the functional layer of the endometrium due to the withdrawal of progesterone and estrogen. ### **Explanation of the Correct Answer** **Option A (2-7 days)** is the clinically accepted normal range for the duration of menstrual bleeding. According to standard physiological texts (like Guyton and Ganong) and FIGO (International Federation of Gynecology and Obstetrics) classifications, a normal period lasts between **3 to 8 days**, with **2 to 7 days** being the most common range tested in medical examinations. The average blood loss during this period is approximately **30–80 mL**. ### **Analysis of Incorrect Options** * **Option B (7-10 days):** Bleeding exceeding 8 days is clinically defined as **prolonged menstrual bleeding** (formerly part of menorrhagia). * **Option C (2 days):** While 2 days is the lower limit of normal, it does not represent the full physiological range. Bleeding lasting less than 2 days is termed **hypomenorrhea**. * **Option D (5-9 days):** This range is too narrow at the start and extends into the pathological range at the end. ### **High-Yield Clinical Pearls for NEET-PG** * **Normal Cycle Length:** 21–35 days (Average: 28 days). * **Average Blood Loss:** 35 mL (Upper limit of normal is 80 mL). * **Terminology Update:** The term "Menorrhagia" is being replaced by **Heavy Menstrual Bleeding (HMB)**, and "Metrorrhagia" by **Intermenstrual Bleeding**. * **Day 1 of Cycle:** Defined as the first day of menstrual bleeding. * **Endometrial Regeneration:** Occurs during the proliferative phase under the influence of **Estrogen**.

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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