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

Correct Answer: D

Rationale: The correct answer is D because testosterone inhibits the hypothalamic secretion of gonadotropin-releasing hormone (GnRH) and the pituitary secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This disruption in the normal hormonal feedback loop leads to the suppression of ovulation and the menstrual cycle. Option A is incorrect because inhibin is not directly affected by testosterone. Option B is incorrect as testosterone does not bind to endometrial receptors directly. Option C is incorrect because testosterone does not stimulate the secretion of FSH and LH from the anterior pituitary.

Correct Answer: A

Rationale: The correct answer is A. Birth control pills containing estrogen and progesterone prevent the preovulatory surge of luteinizing hormone (LH) secretion from the pituitary gland. This leads to the inhibition of ovulation, preventing the release of an egg from the ovary. Without ovulation, fertilization cannot occur, effectively preventing pregnancy. Choice B is incorrect because birth control pills do not prevent the development of ovarian follicles; they prevent ovulation. Choice C is incorrect because suppressing the function of the corpus luteum is not the primary mechanism of action of birth control pills. Choice D is incorrect because birth control pills do not prevent the normal development of the endometrium; they primarily prevent ovulation.

Correct Answer: B

Rationale: The correct answer is B: testis. The seminiferous tubules are located within the testes, where sperm are produced through the process of spermatogenesis. The spermatic cord (A) contains blood vessels, nerves, and the vas deferens but not the seminiferous tubules. The ductus deferens (C) is a tube that carries sperm from the epididymis to the urethra, not where sperm are formed. The epididymis (D) is where sperm mature and are stored but not where they are initially formed. Therefore, the testis is the only choice where the seminiferous tubules are located for sperm production.

Correct Answer: C

Rationale: Rationale: Upon fertilization, an oocyte completes meiosis II, resulting in the formation of the ovum and another polar body. The ovum contains the majority of the cytoplasm and organelles needed for fertilization and embryonic development, while the polar body is a small non-functional cell. This process ensures proper distribution of genetic material and cytoplasm. Incorrect Choices: A: The corona radiata and a polar body are structures associated with the ovulated oocyte, not the result of fertilization. B: The morula and blastocyst are early embryonic stages that form after several cell divisions following fertilization, not products of oocyte meiosis. D: The primary oocyte and secondary oocyte are stages of oocyte development before fertilization and are not produced after fertilization.

Correct Answer: C

Rationale: The correct answer is C: 120 days. Spermatogenesis is the process of sperm production, which involves several stages including mitosis, meiosis, and maturation. It takes around 64 days for the sperm to develop from spermatogonia to mature spermatozoa in the seminiferous tubules. After that, the sperm undergo additional maturation in the epididymis for approximately 12-14 days. Therefore, the entire process of spermatogenesis, from the initial division of spermatogonia to the release of mature sperm, takes approximately 120 days. Choice A (25-50 days) is too short for the complete process of spermatogenesis. Choice B (64-72 days) only covers the time for sperm development in the seminiferous tubules but does not include the maturation period in the epididymis. Choice D (1 year) is too long for spermatogenesis and does not accurately represent the