Gastric hydrochloric acid is secreted from the highly specialized parietal cells located in the corpus of the stomach, generating a H+ concentration in the gastric juice that is 3 million times greater than that in blood and tissue.
Parietal cells contain the enzyme carbonic anhydrase, which promotes the hydration of carbon dioxide. HCO3 - is subsequently exchanged for a Cl- ion which combines with a hydrogen ion to form hydrochloric acid.
The neurotransmitter acetylcholine, the hormone gastrin, and the paracrine (hormone like) histamine are endogenous chemicals that act in concert to stimulate and control acid production by binding to parietal cell surface receptors.
In the stomach, hydrochloric acid’s primary function is to maintain a sterile environment and to initiate the conversion of pepsinogen to pepsin. Hydrochloric acid secretion prevents bacterial or fungal overgrowth of the small intestine, encourages the flow of bile and pancreatic enzymes, and facilitates the absorption of a variety of nutrients, including folic acid, ascorbic acid, beta-carotene, non-heme iron, and some forms of calcium, magnesium, and zinc.
Hydrochloric acid aids in the liberation of iron from food and facilitates its conversion to the ferrous form. Zinc solubility is dependent on pH, with increasing solubility occurring as the pH becomes more acidic.
Approximately 2 L of hydrochloric acid is produced daily. In general, free hydrochloric acid is present in an adequate concentration to maintain a pH between 1 and 2 in the stomach. The pH level in the stomach depending on factors such as food intake, stress, and medications or supplements. An increase in hydrochloric acid and decreasing pH level also signal gastric motility to turn on to move the partially digested bolus of food along and help kill bacteria normally ingested with food.
Numerous studies have shown acid secretion declines with advancing age. The resultant rise in stomach pH can have a detrimental impact on nutrient absorption and may increase the risk of a variety of clinical conditions.
Physiological functions of hydrochloric acid in stomach
