A 20-year-old woman is not having menstrual cycles. Her plasma progesterone concentration is found to be minimal. What is the explanation for the low level of progesterone?

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: 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

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.