Why is milk produced only after delivery, not before?

Correct Answer: B

Rationale: Correct Answer: B - High levels of progesterone and estrogen during pregnancy suppress milk production. Rationale: 1. Progesterone and estrogen levels are high during pregnancy to maintain the uterine lining and support fetal development. 2. These hormones inhibit the action of prolactin, the hormone responsible for milk production. 3. As a result, the mammary glands are prevented from producing milk until after delivery when progesterone and estrogen levels drop. 4. Once these hormone levels decrease, prolactin can initiate milk production in response to the baby's demand for feeding. Summary of other choices: A: Levels of luteinizing hormone and follicle-stimulating hormone do not directly impact milk production during pregnancy. C: Alveolar cells of the breast may have some developmental changes during pregnancy, but it is not the primary reason for milk production post-delivery. D: Oxytocin is involved in milk ejection, not milk production, and its release is

Correct Answer: B

Rationale: The correct answer is B: Ductus venosus. The ductus venosus carries oxygenated blood from the umbilical vein to the inferior vena cava, bypassing the liver. This blood has the highest Po2 among the choices because it is coming directly from the placenta, where oxygen exchange occurs. The other choices (A, C, D) carry deoxygenated blood or blood with lower oxygen content in the fetal circulation. The ductus arteriosus shunts blood from the pulmonary artery to the aorta, so it carries deoxygenated blood. The ascending aorta and left atrium receive mixed oxygenated and deoxygenated blood, not the highest Po2.

Correct Answer: C

Rationale: The correct answer is C: Spermatids are streamlined to form sperm via spermiogenesis. Spermiogenesis is the final stage of spermatogenesis where round spermatids mature into spermatozoa. During spermiogenesis, the spermatids undergo significant structural changes, including the formation of the acrosome, tail, and mitochondria, to become fully functional sperm cells. Choices A and B are incorrect because spermiogenesis does not involve building the stem cell line or producing type A cells. Choice D is incorrect because spermiogenesis does not result in the production of two sperm from one primary spermatocyte; rather, it is the process by which spermatids are transformed into mature sperm cells.

Correct Answer: D

Rationale: The correct answer is D: Bulbourethral fluid. Semen is composed of sperm, seminal fluid, and prostatic fluid. Bulbourethral fluid is not a component of semen but contributes to pre-ejaculatory fluid. This fluid is released from the Cowper's glands and serves to lubricate the urethra prior to ejaculation. The other choices (A, B, C) are all essential components of semen that play crucial roles in sperm transport, nourishment, and protection.

Correct Answer: D

Rationale: The correct answer is D because the innermost lining of the vagina does not slough off periodically like the uterine lining does during menstruation. The vaginal lining is composed of stratified squamous epithelium that does not undergo the shedding process seen in the endometrium. This is important for maintaining the integrity and functionality of the vagina. Choices A, B, and C are true statements about the vagina. A: The vagina serves as the birth canal. B: The distal end of the vagina is partially enclosed by the hymen. C: The vagina is the female organ of copulation.