How is hormone secretion regulated?

Correct Answer: D

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

Correct Answer: A

Rationale: Melatonin, regulating sleep, is secreted by the pineal gland, not listed; however, pituitary (A) is incorrect pineal is intended but missing. Corpus luteum makes progesterone, progesterone's a hormone, melatonin's not a gland. Assuming error, pineal aligns with melatonin's role. This circadian function distinguishes it, key to sleep patterns, contrasting with reproductive or regulatory glands.

Correct Answer: D

Rationale: Pancreas secretes trypsinogen, an inactive enzyme, activated to trypsin in the gut, not directly activating phospholipase A₂ trypsin cleaves proteins, indirectly aiding lipid digestion. It resembles salivary glands (mixed endocrine-exocrine). Enzymes are in acinar zymogen granules, not α-cells (glucagon). It secretes ~1-1.5 L pancreatic juice daily, not 500 mL. Trypsinogen's role distinguishes pancreatic exocrine function, key to digestion, unlike structural, cellular, or volume errors.

Correct Answer: C

Rationale: T4's action is slower than T3's converted to T3 for potency, acting via nuclear receptors over hours. Iodide is actively transported into colloid for synthesis. MIT/DIT (intermediates) aren't secreted only T3/T4. TBG, not albumin, binds most T4 albumin has capacity but lower affinity. Slower T4 action distinguishes it, key to thyroid kinetics, unlike transport, secretion, or binding truths.

Correct Answer: C

Rationale: Thyroid hormones (T3/T4) boost Na/K ATPase (metabolism), nitrogen excretion (catabolism), and α-myosin chains (cardiac efficiency), but don't directly increase catecholamine levels they sensitize tissues to them via β-receptors. Catecholamine production is adrenal, not thyroid-driven. Exclusion of catecholamine increase distinguishes it, key to thyroid's calorigenic scope, unlike metabolic or cardiac effects.