When do progesterone levels rise to their highest point during the female hormonal cycle?

Correct Answer: A

Rationale: Progesterone levels rise to their highest point between ovulation and the beginning of menstruation because this is the luteal phase of the menstrual cycle when the corpus luteum (formed from the ruptured follicle after ovulation) secretes progesterone. This hormone prepares the endometrium for implantation and maintains a potential pregnancy. Explanation for other choices: - B: Immediately before ovulation, estrogen levels are high, not progesterone. - C: Luteinizing hormone surge triggers ovulation, not directly related to progesterone rise. - D: The development of primary follicles is associated with estrogen, not progesterone.

Correct Answer: B

Rationale: The correct answer is B: Peptide or protein hormones have receptors on the cell membrane. These hormones are typically large molecules that cannot pass through the cell membrane, so they bind to receptors on the cell surface to initiate signal transduction pathways. This allows them to quickly and effectively communicate with target cells. A: They do not have longer half-lives than steroid hormones. Peptide hormones are usually rapidly degraded compared to steroid hormones. C: They do not have a slower onset of action than steroid and thyroid hormones. Peptide hormones can have rapid onset of action due to their signaling pathways. D: They can be stored in endocrine-producing glands, such as insulin being stored in pancreatic beta cells.

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.