The two regulatory systems of the body are the endocrine system and the

Correct Answer: A

Rationale: The endocrine and nervous systems regulate body functions: endocrine via hormones (slow, widespread), nervous via neurons (fast, specific). Immune defends, circulatory transports, respiratory oxygenates supportive, not regulatory. This dual control distinguishes them, key to coordination, contrasting with protective or transport systems.

Correct Answer: C

Rationale: The pancreas secretes insulin and glucagon to maintain blood sugar: insulin lowers it by promoting uptake, glucagon raises it via liver glucose release. Pineal (melatonin), pituitary (GH, ACTH), and adrenal (adrenaline) glands affect metabolism indirectly not sugar directly. Pancreas's dual hormonal role distinguishes it, key to glucose homeostasis, contrasting with stress or growth regulators.

Correct Answer: C

Rationale: Insulin, from pancreatic β-cells, is synthesized as proinsulin, cleaved to active form, lowering glucose via membrane receptors (tyrosine kinase). α-cells secrete glucagon, not insulin. It's a dual-chain polypeptide, not triple helical structural misfit. It binds surface receptors, not cytoplasmic steroids do that. Prohormone synthesis distinguishes insulin's production, critical for its activation and glucose regulation, unlike wrong cell origin, structure, or receptor location.

Correct Answer: D

Rationale: Erythropoietin (EPO) production from kidneys is inhibited by theophylline (adenosine antagonist), reducing RBC stimulation in hypoxia. It increases RBC via progenitor division, but takes days, not 24 hours. Inactivation is hepatic/renal, not spleen-specific. Theophylline's suppression distinguishes it, critical for EPO regulation, unlike action, inactivation, or timing claims.

Correct Answer: D

Rationale: PTH inhibits PO₄ reabsorption (increases excretion) in kidneys, lowering serum PO₄ while raising Ca²⁺ dual action defines it. PTH increases Ca reabsorption, not decreases. PO₄ secretion rises, not falls. Calcitonin reduces bone resorption. PTH's PO₄ effect distinguishes it, critical for calcium-phosphate balance, unlike Ca reabsorption, secretion, or calcitonin errors.