Reproductive Physiology — MCQs

Reproductive Physiology Indian Medical PG Practice Questions and MCQs

Question 371: Which hormones antagonize the effect of NO and cause the penis to become flaccid after orgasm?

A. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
B. Endothelin and norepinephrine (Correct Answer)
C. Progesterone and LH
D. Estrogen and progesterone

Explanation: ***Endothelin and norepinephrine*** - **Endothelin** is a potent vasoconstrictor that promotes the contraction of smooth muscle in the penile arteries, reducing blood flow and leading to detumescence. - **Norepinephrine** (a sympathetic neurotransmitter) causes vasoconstriction in the penile arteries and corpus cavernosum, also contributing to flaccidity after orgasm. *Luteinizing hormone (LH) and follicle-stimulating hormone (FSH)* - **LH** stimulates testosterone production in Leydig cells, playing a crucial role in libido and spermatogenesis, but not directly in the process of penile detumescence. - **FSH** is primarily involved in spermatogenesis and the maturation of germ cells, with no direct role in the vascular mechanisms of penile flaccidity. *Progesterone and LH* - **Progesterone** is predominantly a female sex hormone, with only minor roles in male physiology, and does not directly antagonize NO effects in penile detumescence. - As mentioned, **LH** primarily regulates testosterone production and is not involved in post-orgasm flaccidity. *Estrogen and progesterone* - **Estrogen** levels in males are low and primarily involved in bone health and spermatogenesis, not penile detumescence. - **Progesterone** does not play a direct role in the vascular mechanisms leading to penile flaccidity in males.

Question 372: Progesterone production in the ovary is primarily by:

A. Corpora albicans
B. Corpora lutea (Correct Answer)
C. Stroma
D. Mature follicles

Explanation: ***Corpora lutea*** - The **corpus luteum** forms after ovulation from the remnants of the ovarian follicle and is the primary source of **progesterone** during the luteal phase of the menstrual cycle and early pregnancy. - Its main function is to prepare the **endometrium** for implantation and maintain pregnancy. *Corpora albicans* - This is the **scar tissue** left after the degeneration of the **corpus luteum** when pregnancy does not occur. - It is **inactive hormonally** and does not produce significant amounts of progesterone. *Stroma* - The **stroma** is the connective tissue framework of the ovary that supports the follicles. - While it contains cells that can produce some **androgens**, it is not the primary site of **progesterone** production. *Mature follicles* - **Mature follicles** (Graafian follicles) primarily produce **estrogen** in preparation for ovulation. - Although they produce some progesterone just before ovulation, the **corpus luteum** is the main producer after ovulation.

Question 373: Spermatogenesis is mostly controlled by:

A. GnRH
B. LH
C. FSH (Correct Answer)
D. Inhibin

Explanation: ***FSH*** - **Follicle-stimulating hormone (FSH)** acts directly on **Sertoli cells** in the seminiferous tubules, stimulating them to support spermatogenesis and produce **androgen-binding protein (ABP)**. - FSH directly promotes the **proliferation and differentiation of spermatogonia** and is essential for the initiation and maintenance of spermatogenesis. - While spermatogenesis requires both FSH and testosterone working synergistically, **FSH is considered the primary direct regulator** at the Sertoli cell level, making it the best answer when comparing these hormonal options. *LH* - **Luteinizing hormone (LH)** acts on **Leydig cells** to stimulate **testosterone production**, which is absolutely essential for completing spermatogenesis (especially meiosis and spermiogenesis). - However, LH's role is considered **indirect** as it works through testosterone, whereas FSH directly stimulates the Sertoli cells that physically support developing sperm. - Both FSH and testosterone are required; neither alone is sufficient. *GnRH* - **Gonadotropin-releasing hormone (GnRH)** from the hypothalamus controls the release of both LH and FSH from the anterior pituitary gland. - It acts as the **master regulator of the hypothalamic-pituitary-gonadal axis** but does not directly control spermatogenesis at the testicular level. - Its effect is indirect, operating two steps removed from the testes. *Inhibin* - **Inhibin** is produced by **Sertoli cells** in response to FSH and provides **negative feedback** on FSH secretion from the anterior pituitary. - It regulates the regulator (FSH levels) but does not directly control spermatogenesis itself. - It serves as a feedback mechanism to fine-tune FSH levels based on the state of spermatogenesis.

Question 374: Which of the following organs secretes zinc in large amount in man?

A. Epididymis
B. Vas
C. Prostate (Correct Answer)
D. Seminal vesicle

Explanation: ***Prostate*** - The **prostate gland** is a major source of zinc in seminal fluid, where it plays a critical role in **sperm maturation**, motility, and capacitation. - High zinc concentrations are found in prostatic secretions, contributing significantly to the overall zinc content of **semen**. *Epididymis* - The epididymis is primarily involved in the **maturation and storage of sperm**, rather than the secretion of large amounts of zinc. - While it has some zinc, its contribution to the total seminal zinc is much less significant compared to the prostate. *Vas* - The **vas deferens** transports sperm from the epididymis to the ejaculatory duct and does not primarily secrete zinc. - Its main function is **sperm transport**, not the production or secretion of seminal fluid components like zinc. *Seminal vesicle* - The **seminal vesicles** produce a significant portion of the seminal fluid, rich in fructose and prostaglandins, but they are not the primary source of zinc. - Their secretions provide energy for sperm and contribute to semen volume, while zinc is largely from the prostate.

Question 375: The principal steroid secreted by testes is

A. Dehydroepiandrosterone
B. Dihydrotestosterone
C. Androstenedione
D. Testosterone (Correct Answer)

Explanation: ***Testosterone*** - **Testosterone** is the primary **androgen** secreted by the **Leydig cells** in the testes, responsible for male sexual development and characteristics. - It plays crucial roles in **spermatogenesis**, muscle growth, bone density, and libido. *Dehydroepiandrosterone* - **Dehydroepiandrosterone (DHEA)** is a steroid hormone produced mainly by the **adrenal glands**, with a small amount also produced in the gonads. - While it is a precursor to other hormones, it is not the principal steroid secreted by the testes. *Dihydrotestosterone* - **Dihydrotestosterone (DHT)** is a more potent androgen that is converted from **testosterone** in target tissues by the enzyme **5-alpha-reductase**. - It is responsible for many androgenic effects but is not directly secreted by the testes in significant amounts. *Androstenedione* - **Androstenedione** is also an **androgen precursor** produced by both the adrenal glands and the gonads. - It can be converted into **testosterone** or **estrogen**, but it is not the main steroid secreted by the testes.

Question 376: The mammary gland is an estrogen-responsive organ. Which statement is NOT true about estrogen or the mammary gland?

A. Estrogen promotes growth of the duct system
B. Estrogen is produced in the placenta
C. Estrogen is produced primarily by the ovary
D. Estrogen promotes growth of the lobules and acini (Correct Answer)

Explanation: ***Estrogen promotes growth of the lobules and acini*** - This statement is **FALSE**. Estrogen primarily stimulates the **growth of the ductal system** in the mammary gland. - The development of **lobules and acini** (glandular tissue where milk is produced) is predominantly driven by **progesterone**, in cooperation with estrogen, not solely by estrogen. *Estrogen promotes growth of the duct system* - This is a **TRUE** statement. Estrogen is the primary hormone responsible for the **proliferation and elongation of the mammary ducts** during puberty and pregnancy. - It increases the number of epithelial cells within the ducts, preparing the gland for future milk production. *Estrogen is produced in the placenta* - This is a **TRUE** statement. During **pregnancy**, the placenta becomes a major site of estrogen production, particularly **estriol**, ensuring uterine growth and mammary gland development. - This placental estrogen production is critical for maintaining pregnancy and preparing the body for lactation. *Estrogen is produced primarily by the ovary* - This is a **TRUE** statement. In **premenopausal women**, the **ovaries** are the primary source of estrogen, particularly **estradiol**, which regulates the menstrual cycle and reproductive health. - After menopause, other tissues like adipose tissue become more significant for estrogen production through the conversion of androgens.

Question 377: The period of conditioning of sperms before fertilization is known as

A. Spermiogenesis
B. Spermatocytosis
C. Spermeation
D. Capacitation (Correct Answer)

Explanation: ***Capacitation*** - This is the **physiological change** that sperm undergo in the female reproductive tract, making them capable of fertilizing an ovum. - It involves removal of the **glycoprotein coat** and seminal plasma proteins from the sperm surface, enabling them to undergo the acrosome reaction. *Spermiogenesis* - This is the final stage of **spermatozoon development**, where spermatids mature into spermatozoa (sperm). - It involves dramatic morphological changes, such as the formation of a **tail** and an **acrosome**, but does not involve conditioning for fertilization. *Spermatocytosis* - This refers to the process of **meiotic division** of primary spermatocytes into secondary spermatocytes and then spermatids. - It is a part of spermatogenesis, focused on cell division, not the activation of sperm for fertilization. *Spermeation* - This term is **not a recognized biological process** related to sperm conditioning or development. - It appears to be a coined term and does not correspond to any established stage in sperm maturation or function.

Question 378: Positive feedback action of estrogen for inducing luteinizing hormone surge is associated with which of the following steroid hormone ratios in peripheral circulation?

A. High estrogen : high progesterone
B. High estrogen : low progesterone (Correct Answer)
C. Low estrogen : high progesterone
D. Low estrogen : low progesterone

Explanation: ***High estrogen : low progesterone*** - A sustained period of **high estrogen** levels, produced by the developing follicle, is crucial for triggering the **LH surge** through positive feedback. - At this pre-ovulatory stage, **progesterone levels remain relatively low**, as significant progesterone production only begins after ovulation from the corpus luteum. *High estrogen : high progesterone* - While high estrogen is required for the LH surge, **high progesterone levels** would typically occur *after* ovulation, suppressing LH rather than inducing its surge. - High progesterone usually exerts negative feedback on the hypothalamus and pituitary, preventing an LH surge. *Low estrogen : high progesterone* - **Low estrogen** levels are insufficient to exert the positive feedback necessary for an LH surge. - **High progesterone** during this phase would also inhibit GnRH and LH secretion. *Low estrogen : low progesterone* - Neither low estrogen nor low progesterone levels are conducive to the LH surge; this combination often characterizes the **early follicular phase** or the **late luteal phase/menstruation**, where ovarian activity is minimal. - The LH surge requires a specific hormonal milieu involving elevated estrogen.

Question 379: Nutrition to sperms is provided by:

A. Fructose (Correct Answer)
B. Glucose
C. Galactose
D. Starch

Explanation: ***Fructose*** - **Fructose** is the primary sugar present in seminal fluid, providing the main energy source for **sperm motility**. - The seminal vesicles produce a fluid rich in fructose, which is crucial for energizing sperm during their journey through the female reproductive tract. *Glucose* - While glucose is a common energy source, it is not the **primary or most abundant sugar** specifically provided for sperm nutrition in seminal fluid. - Sperm primarily utilize fructose for their energy needs due to its high concentration in the **seminal vesicles' secretions**. *Galactose* - **Galactose** is a monosaccharide, but it is not a significant component of seminal fluid and does not serve as a primary nutrient for sperm. - It is typically metabolized by the liver and is not found in high concentrations in bodily fluids for direct energy provision to cells like sperm. *Starch* - **Starch** is a complex carbohydrate (polysaccharide) found in plant-based foods, not a simple sugar found in bodily fluids. - It needs to be broken down into monosaccharides (like glucose) for absorption and cannot be directly utilized by sperm for energy.

Question 380: Increased LH secretion just before ovulation is due to

A. Positive feed-back by FSH
B. Positive feed-back by progesterone
C. Positive feed-back by relaxin
D. Positive feed-back by estrogen (Correct Answer)

Explanation: ***Positive feed-back by estrogen*** - The surge in **estrogen** from the dominant follicle during the late follicular phase stimulates the hypothalamus and anterior pituitary. - This high level of estrogen switches from negative to **positive feedback**, leading to a dramatic increase in **GnRH** and subsequently **LH** secretion. *Positive feed-back by FSH* - While **FSH** plays a role in follicular development, its primary function is to stimulate estrogen production, not directly trigger the LH surge via positive feedback. - FSH levels actually decline during the late follicular phase as estrogen levels rise, before a small secondary surge alongside LH. *Positive feed-back by progesterone* - **Progesterone** levels are low before ovulation and begin to rise significantly only after the **LH surge** and ovulation, secreted primarily by the corpus luteum. - While progesterone can contribute to a further LH surge in some contexts, it is not the primary initiator of the pre-ovulatory LH surge. *Positive feed-back by relaxin* - **Relaxin** is primarily involved in relaxing pelvic ligaments and softening the cervix, especially during pregnancy. - It does not play a role in the **positive feedback mechanism** that triggers the pre-ovulatory LH surge.

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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