Which one of the following hormones signals the kidneys to control water balance?

Correct Answer: A

Rationale: Vasopressin (ADH) increases water reabsorption in the kidneys.

Correct Answer: D

Rationale: Corticotropes secrete ACTH, not cortisol directly.

Correct Answer: B

Rationale: PTH inhibits phosphate reabsorption in the PCT to increase blood Ca2+. It enhances Ca2+ reabsorption in the DCT, not PCT, and affects osteoblasts, not osteoclasts directly. Calcitonin and oestrogens inhibit osteoclasts.

Correct Answer: B

Rationale: GLUT transporters (e.g., GLUT4) facilitate glucose diffusion across membranes, not requiring energy directly.

Correct Answer: A

Rationale: Uric acid is a product of purine (e.g., adenine, guanine) catabolism, not pyrimidines, glutamine, or urea.