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Gastric acid or stomach acid is the acidic component – hydrochloric acid of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other animals, but is very similar to that of carrion eating carnivores , needing protection from ingesting pathogens .
It consists mainly of hydrochloric acid and acidifies the stomach content to a pH of 1 to 2. [36] [37] Chloride (Cl −) and hydrogen (H +) ions are secreted separately in the stomach fundus region at the top of the stomach by parietal cells of the gastric mucosa into a secretory network called canaliculi before it enters the stomach lumen. [38]
Parietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions of the stomach. [1]
During hydrochloric acid secretion in the stomach, the gastric parietal cells extract chloride anions, carbon dioxide, water and sodium cations from the blood plasma and in turn release bicarbonate back into the plasma after forming it from carbon dioxide and water constituents. This is to maintain the plasma's electrical balance, as the ...
The hormone gastrin and the vagus nerve trigger the release of both pepsinogen and HCl from the stomach lining when food is ingested. Hydrochloric acid creates an acidic environment, which allows pepsinogen to unfold and cleave itself in an autocatalytic fashion, thereby generating pepsin (the active form). Pepsin cleaves the 44 amino acids ...
A lack of hydrochloric acid produced by the stomach is one of the most common age-related causes of a harmed digestive system. [6] Among men and women, 27% experience a varying degree of achlorhydria. US researchers found that over 30% of women and men over the age of 60 have little to no acid secretion in the stomach.
In 1916, Popielski described histamine as a gastric secretagogue of hydrochloric acid. William Beaumont was an army surgeon who in 1825, was able to observe digestion as it took place in the stomach. [55] This was made possible by experiments on a man with a stomach wound that did not fully heal leaving an opening into the stomach.
Chloride is also needed for the production of hydrochloric acid in the stomach. [18] The concentration of chloride in the blood is called serum chloride, and this concentration is regulated by the kidneys. A chloride ion is a structural component of some proteins; for example, it is present in the amylase enzyme.