Reproductive Physiology Practice Questions

Q: As menstruation ends, estrogen levels in the blood rise rapidly. What is the source of the estrogen?

Developing follicles. **Explanation:** The menstrual cycle is governed by the rhythmic fluctuation of hormones. The rise in estrogen immediately following menstruation marks the beginning of the **Follicular Phase** (Proliferative Phase). **1. Why "Developing Follicles" is correct:** As menstruation ends, the pituitary gland secretes **Follicle-Stimulating Hormone (FSH)**. FSH recruits a cohort of primordial follicles to grow. Within these developing follicles, the **Theca interna cells** produce androgens (androstenedione) under the influence of LH. These androgens then diffuse into the **Granulosa cells**, where the enzyme **aromatase** converts them into **Estradiol (Estrogen)**. This is known as the **"Two-Cell, Two-Gonadotropin" theory**. As the follicles grow, estrogen levels rise rapidly to repair the endometrium. **2. Why other options are incorrect:** * **Corpus Luteum:** This structure forms *after* ovulation (Luteal Phase). While it secretes estrogen, its primary product is progesterone. It regresses before menstruation begins, causing the initial drop in estrogen. * **Endometrium:** The endometrium is the *target* organ for estrogen, not the source. Estrogen causes the endometrium to proliferate (thicken). * **Stromal cells:** While ovarian stroma can produce small amounts of androgens, they are not the primary source of the rapid estrogen rise seen in the early-to-mid follicular phase. **High-Yield Clinical Pearls for NEET-PG:** * **Dominant Follicle:** The follicle with the highest density of FSH receptors becomes the "Graafian follicle" and produces the most estrogen. * **Positive Feedback:** When estrogen levels reach a threshold (approx. 200 pg/mL for 48 hours), it triggers the **LH surge**, leading to ovulation. * **Inhibin B:** Produced by granulosa cells in the follicular phase; it provides negative feedback to FSH.

Q: Corpus luteum formation occurs on which day of the menstrual cycle?

15th day. **Explanation:** The **Corpus Luteum** is a temporary endocrine structure formed from the remnants of the Graafian follicle immediately following ovulation. In a standard 28-day menstrual cycle, ovulation typically occurs on the **14th day** (triggered by the LH surge). Therefore, the transformation of the collapsed follicle into the corpus luteum (luteinization) begins on the **15th day**. * **Option A (15th Day):** This marks the beginning of the **Luteal Phase**. Under the influence of Luteinizing Hormone (LH), granulosa and theca cells proliferate and accumulate lipids (lutein) to secrete progesterone, which is essential for maintaining a potential pregnancy. * **Option B (22nd Day):** This is the period of peak corpus luteum activity. Progesterone levels reach their maximum around day 21–22, coinciding with the window of implantation. * **Option C (1st Day):** This represents the onset of menses (Follicular Phase), where the corpus luteum from the previous cycle has already degenerated into the corpus albicans. * **Option D (28th Day):** This is the end of the cycle. In the absence of hCG (pregnancy), the corpus luteum undergoes regression (luteolysis), leading to a drop in progesterone and the start of menstruation. **High-Yield NEET-PG Pearls:** 1. **Life Span:** The corpus luteum has a fixed functional lifespan of approximately **12–14 days** if fertilization does not occur. 2. **Hormone Secretion:** It secretes primarily **Progesterone**, but also Estrogen and Inhibin A. 3. **Rescue Mechanism:** If pregnancy occurs, **hCG** (produced by syncytiotrophoblasts) rescues the corpus luteum, maintaining it until the placenta takes over progesterone production (luteal-placental shift) at around 7–9 weeks.

Q: Which hormone shows no significant change in its levels throughout the menstrual cycle?

Activin. ### Explanation **Correct Option: A (Activin)** Activin is a member of the transforming growth factor-beta (TGF-β) superfamily. Unlike other reproductive hormones, **Activin levels remain relatively constant** throughout the menstrual cycle. Its primary role is to stimulate FSH synthesis and secretion and enhance the action of LH in the ovaries. While it plays a crucial role in the follicular phase by increasing FSH receptor expression on granulosa cells, its systemic concentration does not fluctuate significantly because it is widely expressed in various tissues and is regulated locally (paracrine/autocrine) by its binding protein, **follistatin**. **Why other options are incorrect:** * **Inhibin (B):** Shows significant fluctuations. **Inhibin B** peaks during the mid-follicular phase (secreted by antral follicles), while **Inhibin A** peaks during the mid-luteal phase (secreted by the corpus luteum). * **FSH (C):** Exhibits a distinct peak just before ovulation (the mid-cycle surge) and a secondary rise at the end of the luteal phase to recruit the next cohort of follicles. * **GnRH (D):** The pulse frequency and amplitude of GnRH change dramatically. It pulses faster in the follicular phase (to favor FSH/LH release) and slower in the luteal phase (due to progesterone inhibition). **High-Yield Clinical Pearls for NEET-PG:** * **Inhibin B** is the best biochemical marker for **ovarian reserve**. * **Activin** acts via serine/threonine kinase receptors, whereas most pituitary hormones use G-protein coupled receptors. * **Mnemonic for Inhibins:** Inhibin **B** is for **B**efore ovulation (follicular); Inhibin **A** is for **A**fter ovulation (luteal). * **Follistatin** is the specific antagonist that binds to and neutralizes Activin.

Q: What is the chromosomal number of a primary spermatocyte?

46 XY. **Explanation:** The process of spermatogenesis begins with **spermatogonia** (stem cells), which undergo mitotic division to maintain their population and differentiate into **primary spermatocytes**. 1. **Why Option A is Correct:** Primary spermatocytes are formed by the mitotic division of Type B spermatogonia. Since mitosis preserves the chromosome number, the primary spermatocyte remains **diploid (2n)**. It contains the full complement of **46 chromosomes (44 autosomes + XY sex chromosomes)**. It is only *after* the primary spermatocyte completes Meiosis I that the chromosome number is halved. 2. **Why Incorrect Options are Wrong:** * **Option B (22X):** This represents a haploid state (n) found in secondary spermatocytes or spermatids. * **Option C (22XX):** This is an abnormal chromosomal complement and does not occur in normal male gametogenesis. * **Option D (46 XX):** This is the normal female diploid karyotype. Normal male cells must contain the Y chromosome. **High-Yield NEET-PG Pearls:** * **The "Halving" Point:** The transition from **diploid (2n)** to **haploid (n)** occurs during the first meiotic division (Meiosis I). Therefore, the Primary Spermatocyte is the *last* diploid cell, and the Secondary Spermatocyte is the *first* haploid cell. * **DNA Content vs. Chromosome Number:** While a primary spermatocyte has 46 chromosomes, it has **4n DNA content** because the DNA replicates during the S-phase before entering Meiosis I. * **Duration:** Spermatogenesis takes approximately **74 days** to complete. * **Site:** The entire process occurs in the **seminiferous tubules**, but the final maturation (motility) occurs in the **epididymis**.

Q: The first polar body is extruded at which stage of oogenesis?

Ovulation. ### Explanation The correct answer is **B. Ovulation**. **1. Why Ovulation is Correct:** Oogenesis is a discontinuous process. Primary oocytes are arrested in **Prophase of Meiosis I** (specifically the diplotene stage) from fetal life until puberty. Just before ovulation, the surge of Luteinizing Hormone (LH) triggers the completion of Meiosis I. This division is unequal, resulting in a large **secondary oocyte** and a small, non-functional **first polar body**. Therefore, the extrusion of the first polar body occurs at the time of ovulation. **2. Why Other Options are Incorrect:** * **Menstruation:** This is the shedding of the endometrial lining due to progesterone withdrawal; it does not trigger meiotic divisions. * **Fertilization:** This is the trigger for the completion of **Meiosis II**. When a sperm penetrates the secondary oocyte, it completes its second division, extruding the **second polar body**. * **Menopause:** This marks the cessation of primary oocyte depletion and the end of reproductive cycles; no further oocytes mature or divide. **3. High-Yield Clinical Pearls for NEET-PG:** * **Arrest Points:** Remember "1-P, 2-M." Meiosis **1** arrests in **P**rophase (until ovulation); Meiosis **2** arrests in **M**etaphase (until fertilization). * **Dictyate Stage:** The prolonged resting phase in Prophase I is also known as the dictyate stage. * **Oocyte Potency:** At birth, a female has ~2 million primary oocytes; by puberty, only ~40,000 remain, and only ~400 will ever ovulate. * **LH Surge:** It is the specific trigger that resumes meiosis by overcoming the Oocyte Maturation Inhibitor (OMI).

Q: What is true about fetal circulation?

The heart receives blood with high oxygen saturation.. In fetal circulation, the goal is to prioritize the delivery of oxygenated blood to the most vital organs: the brain and the heart. **Explanation of the Correct Answer:** Oxygenated blood from the placenta travels via the **umbilical vein** and bypasses the liver through the **ductus venosus**. This highly saturated blood (approx. 80% $O_2$) enters the right atrium and is shunted directly into the left atrium via the **foramen ovale**. From the left atrium, it enters the left ventricle and is pumped into the ascending aorta. Consequently, the **coronary arteries** (supplying the heart) and the carotid arteries (supplying the brain) receive the most oxygenated blood in the fetal system. **Why the other options are incorrect:** * **Option A:** The SVC carries deoxygenated blood returning from the upper body. It has the **lowest** oxygen saturation in the fetal heart and is mostly directed toward the right ventricle and the ductus arteriosus. * **Option B:** In the fetus, the **right ventricular pressure is higher** than the left. This is due to high pulmonary vascular resistance (collapsed lungs) and low systemic resistance (placenta). * **Option C:** The brain receives blood from the ascending aorta, which has **high** oxygen saturation (approx. 65-70%) compared to the lower body. **High-Yield NEET-PG Pearls:** * **Highest $O_2$ saturation:** Umbilical vein (80%). * **Lowest $O_2$ saturation:** Umbilical arteries (58%). * **Crista Dividens:** The edge of the foramen ovale that shunts oxygenated blood from the IVC toward the left atrium. * **Closure of Shunts:** The Foramen Ovale closes functionally at birth due to increased left atrial pressure. The Ductus Arteriosus closes due to increased $O_2$ and decreased Prostaglandin $E_2$.

Q: Which of the following statement regarding sexual differentiation of the fetus is TRUE?

SRY protein is the testis determining factor.. ### Explanation **1. Why Option D is Correct:** The primary determinant of sexual differentiation is the **SRY gene** (*Sex-determining Region of the Y chromosome*), located on the short arm of the Y chromosome. This gene encodes the **SRY protein**, also known as the **Testis-Determining Factor (TDF)**. In its presence, the indifferent bipotential gonad differentiates into a testis around the 7th week of gestation. Without SRY, the default pathway leads to ovarian development. **2. Why Other Options are Incorrect:** * **Option A:** Gonadal development begins much earlier, around the **5th to 6th week** of intrauterine life (IUL), as the genital ridges form. * **Option B:** The Y chromosome determines the differentiation of **testes**, not ovaries. Ovarian development occurs in the absence of the Y chromosome (specifically the absence of SRY) and requires two functional X chromosomes. * **Option C:** While external genitalia begin to differentiate around the 9th week, the process is typically completed by the **12th week** of IUL. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Müllerian Inhibiting Substance (MIS/AMH):** Secreted by **Sertoli cells**; causes regression of Paramesonephric (Müllerian) ducts in males. * **Testosterone:** Secreted by **Leydig cells**; stimulates development of Mesonephric (Wolffian) ducts into internal male structures (Epididymis, Vas deferens, Seminal vesicles). * **Dihydrotestosterone (DHT):** Responsible for the differentiation of **external male genitalia** (Penis, Scrotum) and the Prostate. * **Default Pathway:** In the absence of androgens and MIS, the fetus will develop female internal and external genitalia regardless of genetic sex (e.g., Swyer Syndrome, Turner Syndrome).

Q: Which hormone is involved in the milk secretion reflex?

Prolactin. **Explanation:** The process of lactation involves two distinct reflexes: **Milk Secretion (Production)** and **Milk Ejection (Let-down)**. 1. **Why Prolactin is Correct:** Prolactin, secreted by the **anterior pituitary**, is the primary hormone responsible for the **secretion and synthesis** of milk. When an infant suckles, tactile receptors on the nipple send signals to the hypothalamus, which inhibits Dopamine (Prolactin Inhibiting Factor). This leads to a surge in Prolactin, which acts on the alveolar epithelium of the mammary glands to stimulate milk production. 2. **Why Other Options are Incorrect:** * **Oxytocin:** This hormone is responsible for the **Milk Ejection Reflex** (Milk Let-down). It causes the contraction of **myoepithelial cells** surrounding the alveoli, squeezing out already secreted milk. It does not synthesize milk. * **Vasopressin (ADH):** Primarily involved in water reabsorption in the kidneys and vasoconstriction; it has no direct role in lactation. * **Progesterone:** During pregnancy, high levels of progesterone actually **inhibit** the action of prolactin on the breasts, preventing significant milk production until after delivery (when progesterone levels plummet). **High-Yield Clinical Pearls for NEET-PG:** * **Suckling Stimulus:** The strongest stimulus for both Prolactin and Oxytocin release. * **Galactorrhea:** Often caused by Prolactinomas or drugs that antagonize Dopamine (e.g., Metoclopramide, Antipsychotics). * **Lactational Amenorrhea:** High prolactin levels inhibit **GnRH pulsatility**, leading to suppressed LH/FSH and temporary infertility. * **Mnemonic:** **P**rolactin **P**roduces milk; **O**xyto-**C**in **C**ontracts (myoepithelial cells).

Q: Which hormone is primarily responsible for stimulating milk ejection during breastfeeding?

Oxytocin. **Explanation:** The correct answer is **Oxytocin**. The process of breastfeeding involves two distinct hormonal mechanisms: milk production and milk ejection. **1. Why Oxytocin is Correct:** Oxytocin is synthesized in the hypothalamus (paraventricular nuclei) and released by the **posterior pituitary**. In response to the suckling reflex, oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli. This squeeze forces milk into the larger ducts and out through the nipple, a process known as the **Milk Ejection Reflex** (or "Let-down" reflex). **2. Why the Other Options are Incorrect:** * **Prolactin:** While essential for breastfeeding, Prolactin is responsible for the **synthesis and secretion** of milk (lactogenesis) within the alveolar cells, not its ejection. It is secreted by the anterior pituitary. * **Galactogen:** This is not a human hormone; it is a polysaccharide found in some invertebrates (like snails). * **Growth Hormone:** While it has minor galactopoietic effects (maintaining established lactation), it is not the primary stimulus for milk ejection. **High-Yield Clinical Pearls for NEET-PG:** * **The Suckling Reflex:** Suckling inhibits **Dopamine** (Prolactin Inhibiting Factor), leading to increased Prolactin, while simultaneously stimulating the supraoptic and paraventricular nuclei to release Oxytocin. * **Psychological Influence:** The milk ejection reflex is highly sensitive to emotions. Stress or fear can inhibit oxytocin release, whereas the mere cry of a baby can trigger it. * **Uterine Contraction:** Oxytocin released during breastfeeding also causes uterine contractions (involution), helping the uterus return to its pre-pregnancy size and reducing postpartum hemorrhage.

Question 1

As menstruation ends, estrogen levels in the blood rise rapidly. What is the source of the estrogen?

Accepted Answer

Developing follicles

Answer

Corpus luteum

Answer

Endometrium

Answer

Stromal cells of the ovaries

Question 2

Corpus luteum formation occurs on which day of the menstrual cycle?

Accepted Answer

15th day

Answer

22nd day

Answer

1st day

Answer

28th day

Question 3

Which of the following changes occurs during pregnancy?

Accepted Answer

Fibrinogen level increases

Answer

Plasmin level decreases

Answer

Fibrinolytic activity decreases

Answer

Hemodilution does not occur

Question 4

Which hormone shows no significant change in its levels throughout the menstrual cycle?

Accepted Answer

Activin

Answer

Inhibin

Answer

FSH

Answer

GnRH

Question 5

What is the chromosomal number of a primary spermatocyte?

Accepted Answer

46 XY

Answer

22X

Answer

22XX

Answer

46 XX

Question 6

The first polar body is extruded at which stage of oogenesis?

Accepted Answer

Ovulation

Answer

Menstruation

Answer

Fertilization

Answer

Menopause

Question 7

What is true about fetal circulation?

Accepted Answer

The heart receives blood with high oxygen saturation.

Answer

Blood in the superior vena cava (SVC) has more oxygen saturation.

Answer

Pressure in the left ventricle is higher than in the right ventricle.

Answer

The brain receives blood with low oxygen saturation.

Question 8

Which of the following statement regarding sexual differentiation of the fetus is TRUE?

Accepted Answer

SRY protein is the testis determining factor.

Answer

Gonadal development begins at the 10th week of intrauterine life.

Answer

The Y chromosome determines the differentiation of ovaries.

Answer

Female external genitalia development is completed by 10 weeks.

Question 9

Which hormone is involved in the milk secretion reflex?

Accepted Answer

Prolactin

Answer

Oxytocin

Answer

Vasopressin

Answer

Progesterone

Question 10

Which hormone is primarily responsible for stimulating milk ejection during breastfeeding?

Accepted Answer

Oxytocin

Answer

Prolactin

Answer

Galactogen

Answer

Growth Hormone

Reproductive Physiology — MCQs

Reproductive Physiology — MCQs

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