Tropic hormones:

Correct Answer: C

Rationale: Tropic hormones (e.g., TSH, ACTH) from the anterior pituitary stimulate other endocrine glands to release hormones, regulating their activity. Pineal (melatonin) and thymus (thymosin) aren't primary targets, and nervous tissue isn't hormonally stimulated. This gland-targeting role distinguishes tropic hormones, vital for endocrine coordination, contrasting with direct tissue effects.

Correct Answer: D

Rationale: Adrenocorticotropic hormone (ACTH) from the anterior pituitary stimulates adrenal cortisol release, managing stress/metabolism. Aldosterone (adrenal) and angiotensin (RAAS) regulate fluid, ADH controls water not cortisol. ACTH's specific role distinguishes it, key to the HPA axis, contrasting with fluid-regulating hormones.

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.