The structure between the uterus and the vagina is the

Correct Answer: B

Rationale: The correct answer is B: cervix. The cervix is the structure between the uterus and the vagina, serving as the lower part of the uterus that connects to the vagina. It plays a crucial role in pregnancy by allowing sperm to enter the uterus and facilitating the passage of menstrual blood. Rationale: 1. The uterine tube (A) is not the correct answer as it connects the ovaries to the uterus and is not located between the uterus and the vagina. 2. The vulva (C) is the external genitalia and is not the structure between the uterus and the vagina. 3. The hymen (D) is a thin membrane at the opening of the vagina and does not serve as the structure between the uterus and the vagina.

Correct Answer: C

Rationale: The correct answer is C: Increased secretion of oxytocin from the paraventricular nuclei. During breast-feeding, oxytocin is released from the paraventricular nuclei in response to suckling. Oxytocin stimulates the contraction of myoepithelial cells around the alveoli and ducts in the breast, facilitating milk ejection. This response helps in the release of milk for the infant's feeding. Rationale: - Choice A is incorrect because ADH is not directly related to breast-feeding. - Choice B is incorrect because ADH is not primarily released from the paraventricular nuclei in response to breast-feeding. - Choice D is incorrect as neurophysin is not directly involved in the hormonal response during breast-feeding.

Correct Answer: D

Rationale: The correct answer is D because two days before menstruation, the corpus luteum secretes estrogen, progesterone, and inhibin, which collectively suppress the hypothalamus's secretion of GnRH and the pituitary gland's secretion of FSH and LH. This hormonal feedback loop helps prepare the body for menstruation. A: The anterior pituitary gland becoming unresponsive to GnRH does not explain the low FSH and LH levels. B: Estrogen from developing follicles typically exerts a positive feedback on the hypothalamus, not inhibitory feedback. C: The rise in body temperature does not directly impact FSH and LH levels; it is more related to ovulation.

Correct Answer: C

Rationale: The correct answer is C: Progesterone from the corpus luteum. After ovulation, the corpus luteum forms from the ruptured follicle and secretes progesterone. Progesterone is responsible for preparing the endometrium for potential implantation of a fertilized egg by increasing its thickness. Luteinizing hormone (A) triggers ovulation but does not directly affect endometrial thickness. Estrogen from the corpus luteum (B) also plays a role in preparing the endometrium but does not specifically stimulate the increase in thickness. Follicle-stimulating hormone (D) primarily regulates the development of ovarian follicles and does not directly influence endometrial thickness.

Correct Answer: A

Rationale: The correct answer is A: uterine (fallopian) tubes. These tubes receive the ovulated oocyte from the ovary and provide the site for fertilization. The other choices are incorrect because: B: The vagina is the birth canal and site for sperm deposition, not fertilization. C: The ductus deferens is part of the male reproductive system, not involved in fertilization. D: The uterus is where the fertilized egg implants and develops into a fetus, it is not the site for fertilization.