Gastric acid

Gastric acid is hydrochloric acid secreted by parietal cells in the stomach. It creates an acidic environment that aids digestion and limits microbes.

Parietal cell: A stomach cell that secretes hydrochloric acid and intrinsic factor. These cells release the hydrochloric acid that makes gastric acid.
Hydrochloric acid: A strong acid composed of hydrogen chloride dissolved in water. Gastric acid is hydrochloric acid in the stomach’s aqueous contents.
Pepsin: A stomach protease that breaks proteins into smaller peptides. Acid activates its precursor and provides the low pH in which it works.
Bicarbonate: A negatively charged ion that buffers acids and participates in acid–base regulation. Bicarbonate neutralizes acid in the mucus layer and in the duodenum.
Proton pump: A membrane protein that moves protons across a membrane using energy from ATP. The gastric H⁺/K⁺-ATPase pumps protons into the stomach lumen.
pH: A logarithmic measure of hydrogen-ion activity in a solution. Stomach pH expresses the acidity created by secreted hydrogen ions.
Protein digestion: The enzymatic breakdown of proteins into peptides and amino acids. Gastric acid unfolds proteins, making them more accessible to digestive enzymes.
Antacid: A substance that neutralizes stomach acid without directly stopping its secretion. Unlike acid-suppressing drugs, antacids counter acid already present in the stomach.
Histamine H2 receptor: A receptor that binds histamine and activates signaling through the Gs protein pathway. Histamine signaling at this receptor stimulates acid secretion by parietal cells.
Hydrogen ion: A positively charged hydrogen atom, commonly present in water as a hydrated proton. Its concentration gives gastric contents their acidity.

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