How is the pH of stomach maintained?

The pH of the stomach is maintained by a complex system of mechanisms that work together to secrete hydrochloric acid (HCl) and bicarbonate ions (HCO3-) into the stomach lumen. These mechanisms include:

Parietal cells: Parietal cells in the stomach lining are responsible for secreting HCl. HCl is produced by the reaction of carbon dioxide (CO2) and water (H2O) in the presence of the enzyme carbonic anhydrase. The H+ ions produced by this reaction are then pumped into the stomach lumen, while the HCO3- ions are transported into the bloodstream.

Chief cells: Chief cells in the stomach lining secrete pepsinogen, which is converted into the active enzyme pepsin by the acidic environment of the stomach. Pepsin helps to break down proteins in food.

Gastrin: Gastrin is a hormone produced by the stomach lining in response to the presence of food. Gastrin stimulates the parietal cells to secrete HCl and the chief cells to secrete pepsinogen.

Mucus: The stomach lining is protected from the acidic environment by a layer of mucus. Mucus is produced by the mucous cells in the stomach lining and contains glycoproteins, mucins, and lipids that help to form a protective barrier against HCl.

Bicarbonate secretion: The pancreas and duodenum secrete HCO3- into the duodenum, which helps to neutralize the acidic chyme from the stomach. This process is regulated by the hormone secretin, which is released in response to the presence of acid in the duodenum.

These mechanisms work together to maintain the pH of the stomach within a narrow range of 1.5 to 2.0. This acidic environment is necessary for the proper digestion of food and the prevention of bacterial growth.