Sperm production begins in the

Correct Answer: A

Rationale: The correct answer is A: seminiferous tubules. Sperm production starts in the seminiferous tubules of the testes through a process called spermatogenesis, involving the division and maturation of germ cells. The other choices, B: epididymis, C: vas deferens, and D: ejaculatory duct, are incorrect as they are not sites of sperm production but rather play roles in sperm storage, transport, and ejaculation, respectively. The seminiferous tubules are specifically designed for sperm production, making them the correct choice in this context.

Correct Answer: B

Rationale: The correct answer is B: Nitric oxide. Nitric oxide is a potent vasodilator that relaxes smooth muscle in the arterial walls, leading to decreased resistance in the arteries. This results in increased blood flow to the sinuses of the penis, contributing to erectile function. A: Stimulation of the sympathetic nerves innervating the arteries would actually increase resistance by causing vasoconstriction. C: Inhibition of activity of the parasympathetic nerves leading to the arteries would also increase resistance as parasympathetic stimulation typically leads to vasodilation. Therefore, the correct answer is B as it directly causes vasodilation and decreases resistance in the arteries leading to the sinuses of the penis, which is essential for erectile function.

Correct Answer: C

Rationale: The correct answer is C: Estrogen. Before the preovulatory surge in luteinizing hormone, granulosa cells of the follicle primarily secrete estrogen. This hormone plays a crucial role in preparing the uterine lining for implantation and regulating the menstrual cycle. Estrogen also helps in the development of secondary sexual characteristics. Testosterone (Choice A) is mainly produced by the theca cells of the follicle. Progesterone (Choice B) is primarily secreted by the corpus luteum after ovulation. Inhibin (Choice D) is secreted by granulosa cells but primarily functions to inhibit follicle-stimulating hormone (FSH) secretion from the anterior pituitary gland.

Correct Answer: C

Rationale: The correct answer is C: Substance that blocks the actions of follicle-stimulating hormone. By blocking the actions of FSH, sperm production in the testes would be inhibited, leading to effective sterility. FSH plays a crucial role in stimulating sperm production, so blocking its actions would prevent the development of mature sperm. Explanation for why the other choices are incorrect: A: Substance that mimics the actions of luteinizing hormone - Mimicking LH would not necessarily lead to effective sterility in men. B: Substance that blocks the actions of inhibin - Inhibin regulates FSH secretion but blocking it would not directly lead to effective sterility. D: Substance that mimics the actions of gonadotropin-releasing hormone - Mimicking GnRH would not directly impact sperm production and sterility.

Correct Answer: C

Rationale: The correct answer is C: Seminal vesicles. Seminal vesicles produce a thick, yellowish secretion that provides nutrients and activates sperm. This secretion, along with sperm from the testes, forms semen. Bulbourethral glands produce a clear, viscous fluid that lubricates the urethra during sexual arousal (not yellowish). The prostate gland secretes a milky fluid that neutralizes acidic vaginal secretions. The ejaculatory duct is a passageway for semen to travel from the vas deferens to the urethra and does not produce any secretions. Therefore, the seminal vesicles are the correct answer as they specifically produce the described yellowish secretion that nourishes and activates sperm.