When do the testes begin to descend?

Correct Answer: D

Rationale: The correct answer is D: in the fifth month of pregnancy. The testes begin to descend from the abdomen into the scrotum during the fifth month of pregnancy. This process is crucial for proper development and function of the testes. Descending at this stage allows for the testes to be positioned outside the body, which is essential for sperm production as it requires a slightly lower temperature than the internal body temperature. Summary: A: at birth - Incorrect, as the descent of the testes occurs during fetal development, not at birth. B: two months after birth - Incorrect, as the descent happens during pregnancy, not after birth. C: two months prior to birth - Incorrect, as the descent occurs during pregnancy, not prior to birth.

Correct Answer: C

Rationale: The correct answer is C: one ovum. During oogenesis, a primary oocyte undergoes meiosis to produce one mature ovum and three polar bodies. The ovum contains the majority of the cytoplasm and organelles needed for fertilization. The other choices are incorrect because: A: one secondary oocyte - After meiosis I, the primary oocyte develops into one secondary oocyte and one polar body. B: two secondary oocytes - This is not a possible outcome of oogenesis as only one secondary oocyte is produced. D: four ootids - Ootids are the immediate products of meiosis II in oogenesis and are not the final mature gametes like the ovum.

Correct Answer: B

Rationale: The correct answer is B: vestibule. The vestibule is the space between the labia minora, housing the openings of the urethra and vagina. It is a specific anatomical term that describes this precise area. The other choices, A: vulva refers to the external female genitalia as a whole, C: vaginal orifice specifically denotes the opening of the vagina, and D: pudendal cleft is a term not commonly used in anatomy to describe this specific space. Therefore, B is the correct answer as it accurately describes the anatomical structure in question.

Correct Answer: B

Rationale: The correct answer is B: estrogen. Estrogen is responsible for thickening the lining of the uterus during the menstrual cycle in preparation for implantation of a fertilized egg. Follicle-stimulating hormone (FSH) stimulates the growth of ovarian follicles. Luteinizing hormone (LH) triggers ovulation. Progesterone helps maintain the uterine lining during the second half of the menstrual cycle. Estrogen plays a key role in the initial thickening of the uterine lining, making it the correct choice.

Correct Answer: C

Rationale: The correct answer is C: Zona pellucida. The ovum receives the sperm in the zona pellucida, which is a glycoprotein layer surrounding the oocyte. Sperm must first penetrate this layer to fertilize the egg. Choices A and B (Animal pole and Vegetal pole) refer to different regions of the egg and are not directly involved in sperm-egg interaction. Choice D (None of the above) is incorrect because the zona pellucida is indeed where the sperm interacts with the ovum during fertilization.