Which stimuli are known to stimulate parietal cells to secrete hydrochloric acid?

• A. Secretin, glucagon, and somatostatin
• B. Gastrin, histamine, and acetylcholine
• C. Cholecystokinin, motilin, and vasoactive intestinal peptide
• D. Insulin, glucagon, and ghrelin

Answer: (B)

Parietal cell acid secretion is driven by three main secretagogues that work directly or indirectly to turn on the acid pump. Gastrin, released from G cells in the stomach in response to food (peptides and amino acids, stomach stretch), acts directly on parietal cells to stimulate acid release and also prompts histamine release from neighboring ECL cells. Histamine, from those ECL cells, binds H2 receptors on parietal cells and raises cAMP, boosting the proton pump’s activity. Acetylcholine, from vagal nerves during eating, binds M3 receptors on parietal cells to raise intracellular calcium and promote acid secretion, and it also enhances gastrin and histamine release.

In contrast, the other hormones listed tend to inhibit acid secretion or have no direct stimulatory effect on the parietal cells, so they don’t fit as primary stimulants.