A young woman is given daily injections of a substance beginning on the 16th day of her normal menstrual cycle and continuing for 3 weeks. As long as the injections continue, she does not menstruate. The injected substance could be which of the following?

Correct Answer: C

Rationale: The correct answer is C: An inhibitor of progesterone’s actions. Progesterone is responsible for maintaining the uterine lining, and inhibiting its actions would prevent menstruation. Testosterone (A) and FSH (B) do not directly affect menstruation. Prostaglandin E2 (D) is involved in the menstrual process, but inhibiting it would not necessarily stop menstruation.

Correct Answer: D

Rationale: The correct answer is D: No corpus luteum is present. The corpus luteum is responsible for producing progesterone after ovulation. Without a corpus luteum, progesterone levels will be minimal, leading to a lack of menstrual cycles. A: If LH secretion rate is elevated, it would lead to increased corpus luteum formation and progesterone production. B: If LH secretion rate is suppressed, there would be insufficient stimulation for corpus luteum formation and progesterone production. C: FSH is responsible for follicle development, not progesterone production.

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.