Which hormone regulates carbohydrate, protein and fat metabolism in the body and iodine is essential for the synthesis of it?

Correct Answer: D

Rationale: Thyroxine (T4), synthesized in the thyroid using iodine, governs carbohydrate, protein, and fat metabolism, setting cellular energy use. Testosterone (testes) shapes male traits, insulin (pancreas) controls glucose uptake, adrenaline (adrenals) mobilizes energy acutely not broad metabolism. Iodine's necessity for thyroxine synthesis distinguishes it, critical for metabolic health, with deficiencies causing goiter or hypothyroidism, unlike other hormones.

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.

Correct Answer: D

Rationale: High plasma Ca²⁺ reduces 1,25-dihydroxycholecalciferol (active vitamin D) via feedback, inhibiting renal 1α-hydroxylase balances absorption. ~99% filtered Ca is reabsorbed, not 60%. GIT Ca absorption is active (vitamin D-dependent), not mainly passive. Ca binding is proportional to protein levels (e.g., albumin), not inverse. Vitamin D reduction distinguishes it, key to Ca homeostasis, unlike reabsorption, absorption, or binding errors.