The alpha cells of the pancreas secrete _______ which targets the _______.

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: 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.

Correct Answer: A

Rationale: The correct answer is A because glucocorticoids, like cortisol, increase blood glucose levels through gluconeogenesis, elevate fatty acid levels for energy production, and promote amino acid breakdown for energy. This helps the body respond to stress by providing necessary energy sources. Additionally, glucocorticoids can enhance blood pressure to ensure adequate blood flow during stress. Option B is incorrect because glucocorticoids typically increase heart rate and blood pressure to support the stress response. Option C is incorrect as glucocorticoids do not stimulate the release of insulin; instead, they can have an anti-insulin effect. Option D is incorrect as glucocorticoids do not block neurotransmitters but rather modulate the stress response at various levels.