The radius, ulna and humerus forms the ___________ joint.

Correct Answer: B

Rationale: The correct answer is B: Elbow. The radius, ulna, and humerus form the elbow joint. The ulna and humerus articulate at the trochlear notch, forming the hinge joint, while the radius articulates with the humerus at the capitulum, allowing for rotation. This combination of movements allows for flexion and extension of the forearm. The other choices, knee (A), ankle (C), and shoulder (D), involve different bones and joints in the body that do not include the radius, ulna, and humerus.

Correct Answer: D

Rationale: The correct answer is D: primary spermatocyte. Primary spermatocytes are the cells in the seminiferous tubules that progress through the first meiotic division. During this division, primary spermatocytes undergo DNA replication and then divide into two secondary spermatocytes. These secondary spermatocytes will then undergo the second meiotic division to produce haploid spermatids. Explanation for why other choices are incorrect: A: Sertoli cells are supporting cells in the seminiferous tubules but do not undergo meiotic divisions. B: Spermatogonia are the undifferentiated germ cells that give rise to primary spermatocytes but do not progress through meiotic divisions. C: Spermatids are the haploid cells produced after the two meiotic divisions, so they do not progress through the first meiotic division. In summary, primary spermatocytes are the cells that go through the first meiotic division in the seminiferous tubules

Correct Answer: A

Rationale: The correct answer is A: seminiferous tubules. Sperm production starts in the seminiferous tubules of the testes through a process called spermatogenesis, involving the division and maturation of germ cells. The other choices, B: epididymis, C: vas deferens, and D: ejaculatory duct, are incorrect as they are not sites of sperm production but rather play roles in sperm storage, transport, and ejaculation, respectively. The seminiferous tubules are specifically designed for sperm production, making them the correct choice in this context.

Correct Answer: C

Rationale: The correct answer is C because prostaglandin E2 plays a key role in initiating labor by promoting uterine contractions. Administering an antagonist of prostaglandin E2 effects would inhibit this process. Choice A is incorrect as progesterone levels decrease to trigger labor. Choice B is incorrect as luteinizing hormone does not directly influence labor initiation. Choice D is incorrect because mechanical dilation does not inhibit labor initiation but rather can facilitate it.

Correct Answer: B

Rationale: The correct answer is B: Nitric oxide. Nitric oxide is a potent vasodilator that relaxes smooth muscle in the arterial walls, leading to decreased resistance in the arteries. This results in increased blood flow to the sinuses of the penis, contributing to erectile function. A: Stimulation of the sympathetic nerves innervating the arteries would actually increase resistance by causing vasoconstriction. C: Inhibition of activity of the parasympathetic nerves leading to the arteries would also increase resistance as parasympathetic stimulation typically leads to vasodilation. Therefore, the correct answer is B as it directly causes vasodilation and decreases resistance in the arteries leading to the sinuses of the penis, which is essential for erectile function.