The substrate used for sperm metabolism is produced by the _____.

Correct Answer: B

Rationale: The correct answer is B: seminal vesicle. Seminal vesicles produce fructose-rich fluid that serves as a nutrient source for sperm metabolism. This energy supply enables sperm to swim and undergo various metabolic processes. The other choices are incorrect because the prostate produces components of semen, Cowper's gland secretes pre-ejaculatory fluid, and the testes produce sperm cells but not the substrate for sperm metabolism. Thus, the seminal vesicle is the most direct source of the metabolic substrate for sperm.

Correct Answer: D

Rationale: The correct answer is D: stratified squamous epithelium. This type of epithelium is found in the vagina to provide protection against abrasion and infection due to its multiple layers of cells. The stratified nature allows for wear and tear resistance. Simple cuboidal and columnar epithelia are not ideal for this function due to their single layer structure. Mucous epithelium is not a recognized epithelial type.

Correct Answer: C

Rationale: The correct answer is C: estrogens. Estrogens inhibit their own secretion through negative feedback. When estrogen levels rise, they signal the hypothalamus and pituitary gland to decrease the production of gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH), ultimately leading to a decrease in estrogen secretion. This self-regulation maintains hormonal balance in the body. Incorrect choices: A: FSH - FSH stimulates the production of estrogen by the ovarian follicles, so it does not inhibit estrogen secretion. B: LH - LH also plays a role in stimulating estrogen production and does not inhibit its secretion. D: Progesterone - Progesterone is involved in the menstrual cycle and pregnancy but does not directly inhibit estrogen secretion.

Correct Answer: C

Rationale: The correct answer is C: oxytocin. Myoepithelial cells contract to facilitate milk ejection during breastfeeding. Oxytocin is the hormone responsible for stimulating this contraction. Estrogen and progesterone are involved in breast development and preparing for lactation but do not directly stimulate myoepithelial cell contraction. Prolactin is responsible for milk production but does not directly trigger myoepithelial cell contraction.

Correct Answer: A

Rationale: The correct answer is A: Dartos muscle. The Dartos muscle is a layer of smooth muscle in the scrotum that contracts and relaxes to regulate the temperature of the testes by adjusting their distance from the body for temperature control. The other choices are incorrect because: B: Tunica vaginalis is a serous membrane that surrounds the testes, providing support and lubrication. C: Tunica albuginea is a dense fibrous membrane that covers the testes, providing structural support. D: Seminiferous tubules are the site of sperm production in the testes, but do not play a direct role in temperature regulation.