The secretion of which of the following would be least affected by a decrease in extracellular fluid volume?

Correct Answer: D

Rationale: The correct answer is D: Estrogens. When extracellular fluid volume decreases, the body activates the renin-angiotensin-aldosterone system to retain water and sodium. Estrogen is not directly involved in regulating fluid balance, so its secretion would be least affected. CRH (choice A) stimulates the release of cortisol, which affects fluid balance. Arginine vasopressin (choice B) regulates water reabsorption in the kidneys. Dehydroepiandrosterone (choice C) is a precursor to sex hormones, including estrogen.

Correct Answer: A

Rationale: The correct answer is A: glucagon; liver. Alpha cells of the pancreas secrete glucagon, which targets the liver. Glucagon helps increase blood glucose levels by promoting glycogen breakdown in the liver. Melatonin is a hormone produced by the pineal gland, not the pancreas, and does not target the liver. Glucagon does not target the kidney, and calcitonin is produced by the thyroid gland and is involved in regulating calcium levels, not blood glucose levels.

Correct Answer: D

Rationale: The correct answer is D: adrenocorticotropic hormone (ACTH). ACTH is released by the pituitary gland in response to stress or low cortisol levels, stimulating the adrenal glands to release cortisol. Aldosterone (A) regulates electrolyte balance, angiotensin (B) regulates blood pressure, and antidiuretic hormone (C) regulates water balance, but they do not directly stimulate cortisol release. So, ACTH is the correct choice for stimulating cortisol production.

Correct Answer: A

Rationale: The correct answer is A because tropic hormones are hormones that regulate the function of other endocrine glands, such as ACTH (adrenocorticotropic hormone) and TSH (thyroid-stimulating hormone). These hormones stimulate the target glands to release their own hormones. Choice B is incorrect because tropic hormones specifically regulate other endocrine glands. Choice C is incorrect because tropic hormones typically exert their effects by binding to specific receptors on target cells, rather than directly activating genes. Choice D is incorrect because GH (growth hormone) and PRL (prolactin) are not tropic hormones as they do not directly regulate the function of other endocrine glands.

Correct Answer: D

Rationale: The correct answer is D because during protein kinase activation, enzymes phosphorylate many other enzymes, leading to a cascade of signaling events that can trigger multiple responses in a cell. This process amplifies and diversifies the cellular response to hormones. A: Choice A is incorrect because the number of receptors on the cell membrane does not directly relate to the ability of hormones to elicit multiple responses. B: Choice B is incorrect because receptors typically bind to one hormone molecule at a time, not multiple hormones simultaneously. C: Choice C is incorrect because the rapid metabolism of protein kinases does not directly explain why hormones can elicit multiple responses in a cell.