Too little activity of a particular hormone can arise from

Correct Answer: D

Rationale: All listed factors can reduce hormone activity (e.g., gland failure, receptor defects).

Correct Answer: A

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

Correct Answer: B

Rationale: GH acts via somatomedins (IGF-1) to stimulate bone growth.

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.