Which of the following produce antagonistic results?

Correct Answer: A

Rationale: Calcitonin (thyroid) lowers blood calcium, parathyroid hormone (PTH) raises it antagonistic for calcium balance. FSH and LH cooperate in reproduction, ADH and vasopressin are the same, oxytocin/prolactin synergize in lactation. Calcitonin-PTH opposition distinguishes them, key to homeostasis, contrasting with synergistic pairs.

Correct Answer: D

Rationale: Melatonin, from the pineal gland, regulates the sleep-wake cycle, increasing in darkness to promote sleep. Prolactin (pituitary) aids lactation, cortisol (adrenals) manages stress, progesterone (ovaries) supports pregnancy not sleep directly. Melatonin's circadian role distinguishes it, key to biological rhythms, with disruptions affecting sleep, unlike stress or reproductive hormones.

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.