Which statement regarding vasopressin is incorrect?

Correct Answer: B

Rationale: Oxytocin, not vasopressin, stimulates uterine contractions.

Correct Answer: D

Rationale: Osteoblasts build bone matrix and differentiate into osteocytes.

Correct Answer: C

Rationale: Insulin promotes ketone uptake by muscles during glucose abundance, not ketogenesis (a glucagon effect). It increases amino acid uptake and protein synthesis, not catabolism.

Correct Answer: D

Rationale: Chronic low Ca2+ triggers secondary hyperparathyroidism. High Ca2+ suppresses PTH and doesn't cause tetany (low Ca2+ does). ~99% of Ca2+ is in bones, and infant turnover is high but not precisely 80%.

Correct Answer: D

Rationale: PTH binds to membrane G-protein-coupled receptors, while cortisol, aldosterone, 1,25-DHCC, and thyroxine act via intracellular nuclear receptors.