Birth control pills containing combinations of synthetic estrogen and progesterone compounds given for the first 21 days of the menstrual cycle are effective in preventing pregnancy. What is the explanation for their efficacy?

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: 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

Correct Answer: A

Rationale: Estrogens stimulate growth of the endometrium during the proliferative phase by promoting cell proliferation and thickening of the endometrial lining. Estrogens also increase blood flow to the endometrium. Progesterone, on the other hand, prepares the endometrium for implantation and supports pregnancy, but does not directly stimulate growth during the proliferative phase. Insulin and testosterone do not have direct roles in stimulating endometrial growth during this phase.

Correct Answer: A

Rationale: The correct answer is A: bulbo-urethral glands. These glands produce a thick, yellowish secretion known as pre-ejaculate or Cowper's fluid. It serves to nourish and activate sperm. The other choices are incorrect because: B: The prostate gland produces a milky fluid that helps with sperm motility. C: The seminal glands (vesicles) produce a fluid that provides energy for sperm. D: The ejaculatory duct is a passageway for semen to leave the body, it does not produce any secretions.