Which of the following is most descriptive of cAMP?

Correct Answer: A

Rationale: The correct answer is A: Second chemical messenger. cAMP is a second messenger in cellular signaling pathways, relaying signals from extracellular molecules to intracellular targets. It is not a catecholamine (B), steroid (C), or releasing hormone (D). Catecholamines are a class of neurotransmitters, steroids are lipids with different functions, and releasing hormones are secreted by the hypothalamus to stimulate the release of other hormones. Thus, the most descriptive term for cAMP is a second chemical messenger.

Correct Answer: C

Rationale: The correct answer is C because epinephrine is not a steroid hormone. Steroids are synthesized from cholesterol and have a specific chemical structure, while epinephrine is a catecholamine. Cortisol, aldosterone, and testosterone are examples of steroid hormones, but epinephrine belongs to the class of catecholamines. Therefore, C is incorrect. A, B, and D are correct as they accurately list hormones produced by the anterior pituitary gland, posterior pituitary gland, and gonads respectively.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Prolactin is also called lactogenic hormone, as it promotes milk production in the mammary glands. 2. Secreted by the anterior pituitary gland, not the posterior pituitary gland. 3. Milk let-down reflex is primarily controlled by oxytocin, not prolactin. 4. Prolactin does not stimulate the neurohypophysis (posterior pituitary) to synthesize oxytocin. Summary: Choice B is correct because it accurately describes the function of prolactin in promoting lactation. Choices A, C, and D are incorrect due to inaccuracies in the functions and secretion of prolactin.

Correct Answer: C

Rationale: The correct answer is C: PTH. Parathyroid hormone (PTH) stimulates osteoclastic activity, leading to bone resorption. PTH plays a crucial role in regulating calcium levels in the blood. When calcium levels are low, PTH is released to stimulate the release of calcium from bones through osteoclast activity. A: Calcitonin actually inhibits osteoclastic activity, promoting bone formation. B: Androgen is a male sex hormone and does not directly influence bone resorption. D: Thyroxine is a thyroid hormone that regulates metabolism and does not directly affect bone resorption.

Correct Answer: B

Rationale: The correct answer is B because beta cells of the islets of Langerhans are specialized pancreatic cells that secrete insulin, a hormone crucial for regulating blood sugar levels. Insulin helps cells absorb glucose from the bloodstream, lowering blood sugar levels. Choice A is incorrect because the hormone-secreting cells of the adrenal cortex are called adrenal cortical cells, not beta cells. Choice C is incorrect as releasing hormones are typically secreted by the hypothalamus to stimulate the pituitary gland. Choice D is incorrect because steroids are primarily secreted by the adrenal cortex, not the beta cells of the islets of Langerhans.