Which of these hormones is released by the posterior pituitary gland?

Correct Answer: B

Rationale: The correct answer is B: antidiuretic hormone (ADH). ADH is released by the posterior pituitary gland to regulate water balance in the body by controlling the reabsorption of water in the kidneys. Thyroid hormone (A) is produced by the thyroid gland, while glucagon (C) and insulin (D) are produced by the pancreas to regulate blood sugar levels. ADH is the only hormone among the choices that is released by the posterior pituitary gland, making it the correct answer.

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.

Correct Answer: D

Rationale: The correct answer is D because steroids act by binding to intracellular receptors, forming a hormone-receptor complex that directly interacts with the cell's DNA to regulate gene expression. This leads to changes in protein synthesis and cell function. A: Extracellular receptors do not have specificity for a single amino acid sequence on the hormone. Steroids act intracellularly. B: Formation of cyclic AMP is associated with G-protein coupled receptors, not steroid receptors. C: Second-messenger systems are typically involved in signaling cascades triggered by extracellular ligands, not steroids.