Which hormone primarily stimulates gastric acid secretion by the stomach, acting on parietal cells?

• A. Secretin
• B. Gastrin
• C. Ghrelin
• D. Cholecystokinin

Answer: (B)

Gastrin is the primary driver of gastric acid secretion. It is released by G cells in the stomach's antrum in response to peptides, amino acids, and vagal signals. Once in circulation, gastrin acts on parietal cells by binding CCKB (gastrin) receptors to boost the activity of the H+/K+-ATPase proton pumps, increasing HCl production. It also stimulates nearby enterochromaffin-like cells to release histamine, which further enhances acid secretion by acting on H2 receptors on parietal cells. This combination makes gastrin the main hormone that drives acid output in the stomach.

Other hormones play different roles: secretin mainly promotes pancreatic bicarbonate secretion and tends to oppose gastric acid secretion; ghrelin mainly signals hunger; cholecystokinin primarily stimulates pancreatic enzyme release and gallbladder contraction and can slower gastric processes but does not primarily drive parietal cell acid secretion.