Gastric acid, also called
gastric juice or
stomach acid, is a digestive fluid, formed in the
stomach. It is composed of
hydrochloric acid (HCl) .05–0.1
M (roughly 5,000–10,000
parts per million)
potassium chloride (KCl) and
sodium chloride (NaCl). The acid plays a key role in digestion of
proteins, by activating
digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chains of
amino acids. Gastric acid is produced by cells lining the stomach, which are coupled in feedback systems to increase acid production when needed. Other cells in the stomach produce
bicarbonate, a base, to
buffer the fluid, ensuring that it does not become too acidic. These cells also produce
mucus, which forms a viscous physical barrier to prevent gastric acid from damaging the stomach. Cells in the beginning of the small intestine, or
duodenum, further produce large amounts of bicarbonate to completely neutralize any gastric acid that passes further down into the digestive tract.