Which of the labeled endocrine glands secretes hormones that regulate blood calcium levels?

Correct Answer: D

Rationale: Parathyroid glands (often labeled 'E' in diagrams) secrete PTH to raise blood calcium, unlike thyroid (calcitonin, lowers) or others. 'E' aligns with prior answer. This distinguishes PTH's role in calcium homeostasis, vital for nerve and bone function, contrasting with metabolic glands.

Correct Answer: C

Rationale: Acromegaly from pituitary hGH excess in adulthood causes bone thickening, not goiter (thyroid), Graves' (thyroid), Cushing's (cortisol), or gigantism (childhood). This distinguishes acromegaly's adult phenotype, critical for diagnosis, contrasting with childhood growth or thyroid disorders.

Correct Answer: A

Rationale: Adipose tissue produces leptin for appetite control, not insulin (pancreas) or others (mislisted organs). 'E' fits intent. This distinguishes leptin's metabolic role, vital for energy balance, contrasting with pancreatic or gonadal hormones.

Correct Answer: C

Rationale: Chromaffin cells in the adrenal medulla secrete epinephrine, not cortical zones (glomerulosa: aldosterone, fasciculata: cortisol, reticularis: androgens). This distinguishes catecholamine production, key to acute stress, contrasting with steroid zones.

Correct Answer: C

Rationale: Endocrine signaling uses blood vessels to transport hormones (e.g., cortisol) to targets, enabling systemic effects. Neurons signal electrically/chemically, not via blood transport distinct system. Ducts are exocrine (e.g., sweat glands), not endocrine. Membranes facilitate receptor binding, not transport. Blood vessels' role distinguishes endocrine reach, critical for widespread regulation, unlike neural, exocrine, or cellular mechanisms.