The body's major metabolic hormone is released from the:

Correct Answer: B

Rationale: Thyroid hormone (T3/T4) from the thyroid regulates basal metabolic rate, influencing all cells' energy use. Pituitary (GH), thymus (immunity), and hypothalamus (regulatory) hormones don't match this scope. Thyroid hormone's metabolic dominance distinguishes it, key to systemic energy control, contrasting with growth or immune roles.

Correct Answer: C

Rationale: Thyroxine (T4), produced by the thyroid gland, regulates the body's metabolic rate, dictating how cells convert nutrients into energy, impacting heart rate, digestion, and growth. Blood glucose is managed by insulin/glucagon from the pancreas, ovulation by LH/FSH from the pituitary neither thyroxine's role. 'More than one' is incorrect as thyroxine's primary function is singularly metabolic. This specificity distinguishes thyroxine's systemic metabolic influence, critical for energy homeostasis, contrasting with glucose or reproductive hormones.

Correct Answer: B

Rationale: The anterior pituitary produces growth hormone (somatotropin), driving body growth and metabolism. Pineal makes melatonin, hypothalamus regulates via GHRH, adrenals produce adrenaline/cortisol not GH. Pituitary's 'master gland' status and GH secretion distinguish it, critical for development, with hyposecretion stunting growth, contrasting with regulatory or stress glands.

Correct Answer: B

Rationale: Adrenal medulla secretes dopamine (minor), alongside epinephrine/norepinephrine, from chromaffin cells, aiding stress responses. Cortisol, primary glucocorticoid from zona fasciculata, isn't sole corticosterone exists, though less. Oestrogens (from zona reticularis) aren't largest molecular size varies, aldosterone similar. Cortisol has some mineralocorticoid activity (e.g., in excess like Cushing's), not negligible. Dopamine's medullary secretion distinguishes it, key to catecholamine diversity, unlike glucocorticoid exclusivity, size, or activity claims.

Correct Answer: D

Rationale: PTH increases urinary PO₄ excretion by inhibiting reabsorption, lowering serum PO₄ while raising Ca²⁺. Gastrin/glucagon/secretin don't notably inhibit calcitonin calcium does. Calcitonin's half-life is ~10 minutes, not 30. Calcitonin reduces bone resorption, not increases. PTH's phosphate effect distinguishes it, key to calcium-phosphate balance, unlike hormonal, kinetic, or resorption errors.