What do parietal cells in the stomach secrete?

Parietal cells are specialized cells found in the lining of the stomach, and their primary role is to secrete hydrochloric acid (HCl). This secretion plays a crucial role in digestion as it creates an acidic environment in the stomach that is necessary for the activation of digestive enzymes, such as pepsinogen to pepsin. The acidic pH also aids in the breakdown of food and helps to kill potential pathogens.

In contrast, pepsinogen, which is an inactive enzyme precursor, is secreted by chief cells, not parietal cells. Bicarbonate is typically secreted by cells in the pancreas to neutralize stomach acid in the small intestine, and lipase is an enzyme responsible for fat digestion that is also produced by the pancreas. Therefore, the secretion of hydrochloric acid by parietal cells is instrumental for proper digestion and maintaining the stomach's environment for enzymatic activity.