Which hormone produced by the thyroid gland regulates blood calcium levels?

Correct Answer: D

Rationale: Calcitonin, from the thyroid's C-cells, lowers blood calcium by inhibiting osteoclasts, which break down bone. MSH (pituitary) affects pigmentation, oxytocin (hypothalamus/pituitary) aids childbirth, vasopressin (same) regulates water not calcium. Calcitonin's calcium-lowering action distinguishes it, vital for skeletal balance, especially in growth or pregnancy, contrasting with thyroid's metabolic hormones (T3/T4) or unrelated regulators.

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: C

Rationale: Temperature regulation involves endogenous pyrogens (e.g., IL-1) from monocytes, macrophages, and Kupffer cells, raising hypothalamic setpoints in fever. It's hypothalamic, not cortical posterior hypothalamus heats, anterior cools (stimulation causes vasodilation, not hypothermia). Body temperature fluctuates daily, not constant. Pyrogens' mediation distinguishes fever's mechanism, key to immune-thermoregulatory link, unlike integration, regional, or stability 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.