Reproductive Physiology Practice Questions

Q: What is the primary source of progesterone during a normal menstrual cycle?

Corpus luteum. **Explanation:** The correct answer is **A. Corpus luteum.** **1. Why the Corpus Luteum is correct:** During the luteal phase of the menstrual cycle, following ovulation, the remnants of the Graafian follicle undergo a process called **luteinization**. Under the influence of Luteinizing Hormone (LH), the granulosa and theca cells transform into the corpus luteum. This temporary endocrine structure becomes the primary factory for **progesterone** production. Progesterone is essential for preparing the endometrium for implantation (secretory phase) and maintaining early pregnancy until the placenta takes over (luteal-placental shift). **2. Why other options are incorrect:** * **Ovarian stroma:** This consists of connective tissue, blood vessels, and interstitial cells. While the stroma produces small amounts of androgens (like androstenedione), it is not the primary source of progesterone. * **Surface epithelium:** This is a single layer of cuboidal cells covering the ovary. Its primary role is structural and regenerative; it does not have an endocrine function related to progesterone secretion. **3. NEET-PG High-Yield Pearls:** * **Peak Progesterone:** Progesterone levels peak approximately **7 days after ovulation** (Day 21 of a 28-day cycle). * **The Luteal-Placental Shift:** The corpus luteum is the sole source of progesterone for the first **7–9 weeks** of pregnancy. After this, the placenta (syncytiotrophoblast) takes over. * **Hormonal Trigger:** LH is the primary hormone that maintains the corpus luteum in a non-pregnant cycle, while **hCG** (human Chorionic Gonadotropin) rescues it if fertilization occurs. * **Diagnostic Value:** A serum progesterone level >3 ng/mL is often used as biochemical evidence that ovulation has occurred.

Q: Which of the following is not a phase of the endometrium?

Ovulatory phase. The endometrial cycle refers specifically to the histological changes occurring in the **uterine lining** in response to ovarian hormones. While the ovary undergoes an "ovulatory phase," the endometrium does not. ### Why "Ovulatory Phase" is the Correct Answer Ovulation is an **ovarian event**, not an endometrial one. It refers to the release of the secondary oocyte from the Graafian follicle triggered by the LH surge. During this brief transition, the endometrium is simply finishing its proliferative stage and beginning its secretory transformation; there is no distinct histological "ovulatory phase" of the uterine lining. ### Explanation of Other Phases * **Proliferative Phase (Option D):** Occurs under the influence of **estrogen**. It involves the growth of endometrial glands and stromal vessels. It corresponds to the follicular phase of the ovary. * **Progestational Phase (Option A):** Also known as the **Secretory Phase**. It occurs after ovulation under the influence of **progesterone** from the corpus luteum. Glands become tortuous and begin secreting glycogen-rich fluid to prepare for implantation. * **Menstrual Phase (Option B):** Triggered by the withdrawal of progesterone and estrogen (involution of the corpus luteum), leading to the shedding of the *stratum functionale*. ### NEET-PG High-Yield Pearls * **Dating the Endometrium:** The most reliable histological sign of recent ovulation is **subnuclear vacuolation** in the endometrial glands (early secretory phase). * **Master Regulator:** Estrogen drives proliferation (mitosis), while Progesterone drives secretion and limits proliferation. * **Duration:** The secretory phase is constant at **14 days**, whereas the proliferative phase varies in length, determining the overall cycle duration.

Q: The umbilical venous pO2 is what?

30-32 mmHg. ### Explanation The correct answer is **30-32 mmHg**. **Underlying Concept:** In fetal circulation, the **umbilical vein** is unique because it carries oxygenated blood from the placenta to the fetus. Despite being "oxygenated," the fetal $pO_2$ is significantly lower than adult arterial levels (approx. 95-100 mmHg). This is due to the high metabolic demand of the placenta and the diffusion gradient required for oxygen transfer. The umbilical venous $pO_2$ typically ranges between **30-35 mmHg**, with a saturation of approximately 70-80%. The fetus compensates for this "relative hypoxia" by having a higher concentration of **Fetal Hemoglobin (HbF)**, which has a higher affinity for oxygen. **Analysis of Options:** * **A (20-25 mmHg):** This value is too low for the umbilical vein; it more closely resembles the $pO_2$ of the **umbilical arteries** (approx. 15-25 mmHg), which carry deoxygenated blood back to the placenta. * **B (25-48 mmHg):** While 30 mmHg falls within this range, the upper limit (48 mmHg) is physiologically inaccurate for fetal venous blood. * **D (40-45 mmHg):** This range is too high. By the time blood reaches the fetal heart and is pumped to the upper body, the $pO_2$ has already dropped due to mixing in the IVC (via ductus venosus). **High-Yield Clinical Pearls for NEET-PG:** * **Highest $pO_2$ in Fetus:** The **Umbilical Vein** (30-32 mmHg). * **Lowest $pO_2$ in Fetus:** The **Umbilical Arteries** (15-25 mmHg). * **HbF Shift:** The oxygen-dissociation curve for HbF is shifted to the **left** compared to adult HbA, allowing the fetus to bind oxygen more effectively at lower partial pressures. * **Double Haldane Effect:** This facilitates $CO_2$ transfer from the fetus to the mother, while the **Double Bohr Effect** facilitates $O_2$ transfer from the mother to the fetus.

Q: Ovaries secrete all of the following hormones except?

Dihydrotestosterone. **Explanation:** The correct answer is **D. Dihydrotestosterone (DHT)**. **1. Why Dihydrotestosterone is the correct answer:** The ovary is capable of synthesizing various steroid hormones from cholesterol via the Δ5 and Δ4 pathways. However, **Dihydrotestosterone (DHT)** is not a primary secretory product of the ovary. DHT is a potent androgen formed primarily in **peripheral tissues** (such as the skin and hair follicles) through the action of the enzyme **5-α-reductase** on testosterone. While the ovary produces testosterone, it lacks significant 5-α-reductase activity to secrete DHT directly into the circulation. **2. Analysis of incorrect options:** * **A. Androstenedione:** This is the primary androgen secreted by the **Theca cells** of the ovary. It serves as the immediate precursor for estrone and testosterone. * **B. 17-α-Hydroxyprogesterone:** This is an intermediate in the steroidogenic pathway (produced from progesterone or 17-α-hydroxypregnenolone) and is secreted by the ovary, particularly during the luteal phase. * **C. Dehydroepiandrosterone (DHEA):** The ovary secretes small amounts of DHEA (about 20% of circulating DHEA), though the majority originates from the adrenal cortex. **3. NEET-PG High-Yield Pearls:** * **Two-Cell, Two-Gonadotropin Theory:** LH stimulates **Theca cells** to produce androgens (Androstenedione/Testosterone); FSH stimulates **Granulosa cells** to convert these androgens into estrogens via the enzyme **Aromatase**. * **Potency:** DHT is the most potent natural androgen, followed by Testosterone, then Androstenedione. * **Clinical Correlation:** In Polycystic Ovary Syndrome (PCOS), there is an elevation in ovarian androstenedione and testosterone, but the hirsutism is often driven by the peripheral conversion of these precursors to **DHT** in the skin.

Q: Which of the following is NOT produced by the ovary?

Gonadotropin. ### Explanation **1. Why Gonadotropin is the Correct Answer:** Gonadotropins, specifically **Follicle-Stimulating Hormone (FSH)** and **Luteinizing Hormone (LH)**, are peptide hormones synthesized and secreted by the **gonadotroph cells of the anterior pituitary gland**. Their primary role is to stimulate the ovaries (and testes) to produce sex steroids and gametes. Since they are the *stimulators* of the ovary rather than products *of* the ovary, they are the correct answer. **2. Why the Other Options are Incorrect:** * **Estrogen:** This is the primary female sex hormone produced by the **granulosa cells** of the ovarian follicles (via the aromatization of androgens). * **Testosterone:** While often considered a male hormone, the ovary (specifically the **theca cells**) produces androgens like androstenedione and testosterone. Most of this is converted to estrogen, but some is secreted into the systemic circulation. * **Inhibin B:** This is a glycoprotein hormone secreted by the **granulosa cells** of the developing follicles. It provides negative feedback to the anterior pituitary to specifically inhibit FSH secretion. **3. High-Yield Clinical Pearls for NEET-PG:** * **Two-Cell, Two-Gonadotropin Theory:** LH stimulates **Theca cells** to produce androgens (Cholesterol → Androstenedione); FSH stimulates **Granulosa cells** to convert those androgens into Estrogen (via Aromatase). * **Inhibin Markers:** **Inhibin B** is a marker of follicular reserve (produced by small antral follicles), while **Inhibin A** is produced by the corpus luteum. * **Human Chorionic Gonadotropin (hCG):** Although it is a gonadotropin, it is produced by the **syncytiotrophoblast** of the placenta, not the ovary.

Q: Which is the shortest stage in the human sexual response cycle?

Orgasm. **Explanation:** The human sexual response cycle, as described by Masters and Johnson, consists of four distinct phases: Excitement, Plateau, Orgasm, and Resolution. **Why Orgasm is the correct answer:** The **Orgasm phase** is the shortest stage of the cycle, typically lasting only **3 to 15 seconds**. Physiologically, it is characterized by involuntary rhythmic muscular contractions of the pelvic floor (bulbocavernosus muscle), the uterus/vagina in females, and the prostate/seminal vesicles in males. It represents the peak of physical pleasure and the discharge of accumulated neuromuscular tension. **Analysis of Incorrect Options:** * **Excitement:** This is the initial phase triggered by physical or psychological stimuli. It can last from several minutes to several hours, making it significantly longer than the orgasmic phase. * **Resolution:** This is the final phase where the body returns to its normal physiological state. In males, this includes a "refractory period." This process generally takes 10 to 30 minutes, but can last longer. * **Desire Phase:** This was added later by Helen Singer Kaplan (the Triphasic Model). It represents the psychological urge or drive for sexual activity and has no fixed duration, often lasting much longer than the physiological act itself. **High-Yield NEET-PG Pearls:** * **Masters and Johnson Model:** Excitement → Plateau → Orgasm → Resolution (EPOR). * **Kaplan’s Model:** Desire → Excitement → Orgasm. * **Neurological Control:** The **Excitement** phase (erection) is primarily **Parasympathetic** (S2-S4), while **Orgasm/Emission** is primarily **Sympathetic** (T11-L2). Remember: "Point (Parasympathetic) and Shoot (Sympathetic)." * **Refractory Period:** This occurs only in males during the Resolution phase, during which further orgasm is physiologically impossible. Females do not have a definitive refractory period and are capable of multiple orgasms.

Q: Spermatozoa obtain their nourishment from which of the following?

Fructose. **Explanation:** The correct answer is **Fructose**. **Why Fructose is the correct answer:** Spermatozoa require a constant energy source for motility and survival. The **seminal vesicles** secrete a thick, alkaline fluid that constitutes about 60-70% of the total semen volume. This fluid is rich in **fructose**, which serves as the primary glycolytic fuel for sperm. Unlike most cells in the body that prefer glucose, spermatozoa have adapted to utilize fructose via the GLUT-5 transporter. Fructose provides the necessary ATP through anaerobic and aerobic pathways to power the flagellar movement (motility) required for the journey through the female reproductive tract. **Why other options are incorrect:** * **Glucose:** While glucose can be metabolized by sperm, it is not the primary sugar provided in the seminal vesicle secretion. * **Galactose & Lactose:** These are milk sugars. Galactose is primarily metabolized in the liver, and lactose is a disaccharide found in dairy. Neither is present in significant quantities in seminal fluid nor serves as a physiological energy source for sperm. **High-Yield NEET-PG Pearls:** * **Site of Secretion:** Fructose is exclusively produced by the **seminal vesicles**. * **Clinical Correlation:** In cases of obstructive azoospermia (e.g., congenital bilateral absence of the vas deferens or CBAVD), a **fructose test** is performed on the semen. The **absence of fructose** indicates a blockage or absence of the seminal vesicles. * **Prostaglandins:** Seminal vesicles also secrete prostaglandins, which help thin the cervical mucus and induce retrograde contractions in the female reproductive tract to aid sperm transport. * **pH:** Seminal fluid is alkaline, which helps neutralize the acidic environment of the vagina.

Question 1

A female athlete who took testosterone-like steroids for several months stopped having normal menstrual cycles. What is the best explanation for this observation?

Accepted Answer

Testosterone inhibits the hypothalamic secretion of GnRH and the pituitary secretion of LH and FSH.

Answer

Testosterone stimulates inhibin production from the corpus luteum.

Answer

Testosterone binds to receptors in the endometrium, resulting in the failure of the endometrium to develop during the normal cycle.

Answer

Testosterone binds to receptors in the anterior pituitary that stimulate the secretion of FSH and LH.

Question 2

What is the primary source of progesterone during a normal menstrual cycle?

Accepted Answer

Corpus luteum

Answer

Ovarian stroma

Answer

Surface epithelium of the ovary

Answer

None of the above

Question 3

Which of the following is not a phase of the endometrium?

Accepted Answer

Ovulatory phase

Answer

Progestational phase

Answer

Menstrual phase

Answer

Proliferative phase

Question 4

The umbilical venous pO2 is what?

Accepted Answer

30-32 mmHg

Answer

20-25 mmHg

Answer

25-48 mmHg

Answer

40-45 mmHg

Question 5

Which of the following is NOT a normal phase in the physiology of normal sexual arousal and orgasm?

Accepted Answer

Erogenous Phase

Answer

Plateau Phase

Answer

Orgasm

Answer

Refractory Period

Question 6

Testosterone is produced in Leydig cells in the fetus due to which of the following?

Accepted Answer

ssHCG

Answer

FSH

Answer

Cortisol

Answer

Estrogen

Question 7

Ovaries secrete all of the following hormones except?

Accepted Answer

Dihydrotestosterone

Answer

Androstenedione

Answer

17-α-Hydroxyprogesterone

Answer

Dehydroepiandrosterone

Question 8

Which of the following is NOT produced by the ovary?

Accepted Answer

Gonadotropin

Answer

Testosterone

Answer

Estrogen

Answer

Inhibin B

Question 9

Which is the shortest stage in the human sexual response cycle?

Accepted Answer

Orgasm

Answer

Excitement

Answer

Resolution

Answer

Desire phase

Question 10

Spermatozoa obtain their nourishment from which of the following?

Accepted Answer

Fructose

Answer

Glucose

Answer

Galactose

Answer

Lactose

Reproductive Physiology — MCQs

Reproductive Physiology — MCQs

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