Which GI hormone stimulates gastric acid secretion?

• A. Gastrin
• B. Secretin
• C. Cholecystokinin
• D. Gastric inhibitory peptide

Answer: (A)

Gastrin stimulates gastric acid secretion. G cells in the stomach release gastrin in response to peptides, amino acids, and stomach distension, and even vagal signals. Gastrin acts on parietal cells to increase acid (HCl) production by boosting the activity of the hydrogen-potassium ATPase pumps, and it also stimulates nearby enterochromaffin-like cells to release histamine, which further enhances acid secretion. This gastric-phase response is regulated by negative feedback from the low pH of the stomach and by somatostatin. Other hormones in the list have different primary roles: secretin promotes bicarbonate release and dampens acid secretion; cholecystokinin mainly targets the pancreas and gallbladder and can slow gastric activity; gastric inhibitory peptide inhibits acid secretion and motility while promoting insulin release. So gastrin best explains the stimulation of gastric acid secretion.