Stomach acid, or gastric acid, is a digestive fluid primarily composed of hydrochloric acid, or HCl. The stomach acid also contains potassium chloride and sodium chloride, which are less significant in the digestive process. The stomach acid is very important in the activation of certain enzymes and in protein digestion. The stomach acid is also protective against invading microorganisms.
Production and Regulation of Stomach Acid
Stomach acid is produced by parietal cells, which are mostly abundant in the upper portion and lower regions of the stomach. The activation and secretion of stomach acid is very complex and can be modulated by various stimuli, which include nervous and mechanical stimulation of parietal cells. The normal pH of stomach acid is between 1 to 2; when the pH of stomach acid is higher than normal, stomach acid production is increased, and the opposite is true when the pH is lower than normal.
Protein Digestion
The digestion of proteins begins in the stomach because the enzyme involved in the process is activated in the stomach; pepsinogen, involved in protein digestion and produced by the chief cells of the stomach, is activated by stomach acid. Upon activation, pepsinogen is converted to pepsin, which is the active form. Pepsin is very efficient when the food we eat is chewed properly; if food is not chewed properly, a greater proportion is left undigested as it proceeds to the small intestine.
Too Much Stomach Acid
It is important for stomach acid to be tightly regulated, since acid can potentially destroy the lining of the stomach, leading to ulcer formation and stomach wall perforation. Stomach acid can be excessive when there is increased stimulation of the parietal cells by an abnormal nervous system. Certain cancers of the small intestine can result in the excess production of certain hormones that stimulate acid production; these cancers are often resistant to factors that inhibit stomach acid production.
Too Little Stomach Acid
In some people, the immune system is hyperactive and can attack parietal cells; destruction of the parietal cells results in decreased stomach acid production. Gastritis, or inflammation of the stomach lining, as a result of infection can also lead to destruction of parietal cells. Helicobacter pylori is a bacteria that commonly causes stomach inflammation. Low acid production increases the risk for infection.
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