Concerning Ca metabolism

Correct Answer: A

Rationale: PTH decreases serum PO₄ by increasing renal excretion, raising Ca²⁺ net effect is PO₄ reduction. Vitamin D increases Ca/PO₄ absorption, reducing excretion opposite claim. Calcitonin is from thyroid C-cells, not parathyroid. Insulin promotes bone formation (anabolic), not decreases. PTH's PO₄-lowering distinguishes it, key to calcium-phosphate regulation, unlike vitamin D, calcitonin, or insulin errors.

Correct Answer: D

Rationale: Local hormones and paracrine hormones act on nearby cells without bloodstream travel e.g., prostaglandins (local) or growth factors (paracrine). Autocrine hormones target the secreting cell, circulating hormones travel via blood (e.g., insulin). 'Both 1 and 2' (local and paracrine) fits, as both share this localized action. This distinguishes short-range endocrine signaling, key to tissue-specific responses like inflammation, contrasting with systemic hormone effects.

Correct Answer: C

Rationale: An antagonistic effect occurs when one hormone opposes another e.g., insulin lowers glucose, glucagon raises it not synergistic (cooperative), permissive (enabling), circulating (delivery), or local (proximity). This opposition distinguishes endocrine balance, vital for homeostasis, contrasting with cooperative or static effects.

Correct Answer: A

Rationale: Insulin from pancreatic beta cells lowers blood glucose by promoting uptake and storage, unlike glucagon (raises glucose), somatostatin (inhibits), or thyroid/calcitonin (metabolism/calcium). This distinguishes insulin's hypoglycemic action, key to diabetes management, contrasting with opposing or unrelated hormones.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.