Gastric acid gastric acid, verifying that acid played a crucial role in digestion. Gastric acid Gastric acid, gastric juice or stomach acid, is a digestive fluid formed in the stomach and is composed of hydrochloric acid (HCl), 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 in the lining of the stomach, which are coupled in feedback systems to increase acid production when needed. Other cells in
Extracellular digestion down outside the cell either mechanically or with acid by special molecules called enzymes. Then the newly broken down nutrients can be absorbed by the cells nearby. Humans use extracellular digestion when they eat. Their teeth grind the food, enzymes and acid in the stomach liquefy it, and additional enzymes in the small intestine break the food down into parts their cells can use. Although fungi do not have a digestive tract like humans, they still use extracellular digestion. Fungi and other decomposers utilize nutrients derived from breaking down the substrate they grow on. Another example of extracellular digestion being