Stomach acid, or gastric juice, is secreted by the stomach and plays crucial roles in health and disease. Stomach acid helps with the breakdown of food directly, and also makes an enzyme which breaks food down further. An often overlooked function of stomach acid is its antiseptic properties of killing off bacteria and other microorganisms in the stomach. Stomach acid regurgitation, along with bile, can lead to gastroesophageal reflux disease, or GERD.
Hydrochloric Acid
The main ingredient of stomach acid is hydrochloric acid, or HCL, which explains why stomach acid has such a low or acidic pH scale rating of about 2. According to "Practical Gastroenterology and Hepatology," the strength of the stomach's hydrochloric acid is about 0.5 percent, or 5,000 parts per million. Within the stomach lining, it's the oxyntic or parietal cells that secrete the hydrochloric acid components in high concentrations, but not as HCL directly because the acidity would kill the parietal cells. Instead, atoms of hydrogen and chloride are secreted separately into the micro canaliculi along with other components, where the HCL is synthesized and becomes diluted. HCL secretion is stimulated by three compounds which all have receptors in the stomach lining: histamine, acetylcholine and gastrin.
Stomach acid is actually present in gastric juice in three slightly different forms: concentrated hydrogen ions, which is acid in "free-form"; non-ionized HCL, which is hydrochloric acid combined with other compounds; and titrable HCL acid, which is free-form acid combined with the non-ionized hydrochloric compounds, as cited in "Practical Gastroenterology and Hepatology."
Specifically, the highly acidic nature of the stomach causes proteins from food to denature, which exposes the protein's peptide bonds to the enzyme pepsin. The result is that protein gets broken down into amino acids, which are absorbed by the body and utilized for various purposes.
Potassium Chloride
Another ingredient in stomach acid is potassium chloride, or KCI, which is a salt present in varying amounts. Potassium chloride is not involved in the breakdown of food, but it is the main positive ion inside the body's cells, according to "Human Biochemistry and Disease." Potassium is used for various bodily functions, such as the beating of the heart, nerve conduction, muscle contraction and kidney filtration. Potassium also helps maintain the body's electrolyte and water levels.
Sodium Chloride
The final ingredient in stomach acid is sodium chloride, or NaCl, a common salt also present in varying amounts. Sodium chloride is not directly involved in the breakdown of food, but it does have some antiseptic properties. Sodium chloride is an essential salt for all body fluids, especially the blood. Sodium chloride aids in muscle relaxation and plays an important role in nutrient uptake by cells, as cited in "Human Biochemistry and Disease."
References
- "Gastroenterology": The burden of selected digestive diseases in the United States
- "Practical Gastroenterology and Hepatology: Esophagus and Stomach"; Nicholas J. Talley, M.D., Ph.D.; 2010
- "Human Biochemistry and Disease"; Gerald Litwack, Ph.D.; 2008
