ANP

Correct Answer: D

Rationale: Atrial natriuretic peptide (ANP), from stretched atria, counters angiotensin II by promoting natriuresis, vasodilation, and lowering blood pressure, opposing angiotensin II's sodium retention and vasoconstriction. It inhibits vasopressin (ADH), not stimulates. Scuba diving (pressure) may increase ANP via atrial stretch, not decrease. ANP is a single-chain peptide, not dual helix. Its antagonistic action distinguishes it, key to fluid balance, unlike vasopressin support, diving effects, or structural claims.

Correct Answer: D

Rationale: Insulin release from β-cells involves glucose metabolism, depolarizing the membrane, opening Ca²⁺ channels for exocytosis core mechanism. β-cells are ~60-80%, not 90%. D cells secrete somatostatin, not pancreatic polypeptide (PP cells). Pork insulin, not beef, is closer to human (1 amino acid difference vs. 3). Ca²⁺-driven release distinguishes insulin secretion, critical for glucose response, unlike cell proportion, hormone, or species errors.

Correct Answer: D

Rationale: ACE inhibitors reduce angiotensin II, decreasing thirst in hypovolemia angiotensin II acts on subfornical organ, not just supraoptic nucleus (ADH site). Drinking and ADH differ thirst is behavioral, ADH hormonal. Dry membranes signal hypothalamus (e.g., via osmoreceptors), but angiotensin II's role is primary in volume loss. ACE inhibition distinguishes thirst modulation, key to RAAS-thirst link, unlike site, regulation, or membrane claims.

Correct Answer: A

Rationale: Insulin uses tyrosine kinase receptors (membrane-bound), driving glucose uptake via signaling cascades. Glucagon, PTH, and ACTH use G-protein-coupled receptors (GPCRs), activating cAMP similar mechanism. Insulin's distinct receptor type distinguishes it, key to its anabolic action, unlike cAMP-mediated hormones.

Correct Answer: A

Rationale: Growth hormone (GH) from the anterior pituitary promotes body growth by stimulating protein synthesis and cell division, unlike prolactin (milk production) or thyrotropin (thyroid stimulation). Though options are cut off, 'A' aligns with GH's role. This distinguishes GH's systemic anabolic effects, essential for development, contrasting with lactation or metabolic regulators.