Which is TRUE?

Correct Answer: D

Rationale: Glucagon stimulates somatostatin secretion from D cells. It also increases insulin secretion, somatostatin inhibits it, diazoxide inhibits it, and K^+ depletion reduces it.

Correct Answer: D

Rationale: Aerobic metabolism yields 38 mol ATP per mol glucose via glycolysis, TCA cycle, and oxidative phosphorylation.

Correct Answer: B

Rationale: Most iron absorption occurs in the duodenum/upper jejunum. Dietary iron is mostly ferric, ferritin stores thousands of atoms, ~70% of body iron is in hemoglobin, and absorption is ~10-15%.

Correct Answer: D

Rationale: Secretin inhibits gastrin secretion and stimulates HCO_3-rich pancreatic juice, not enzymes; it doesn't increase acid or emptying time.

Correct Answer: A

Rationale: The production of thyroid hormone is dependent on the intake of protein and iodine.