Gastric secretion of H+ ions

Gastric parietal cells are highly specialized for their unusual task of secreting concentrated acid. The cells are packed with mitochondria that supply energy to drive the apical H, K-ATPase, or proton pump, that moves H+ ions out of the parietal cell against a concentration gradient of more than is terminated after the meal moves from the stomach into the small intestine. Gastric parietal cells are highly specialized for their unusual task of secreting concentrated acid. The cells are packed with mitochondria that supply energy to drive the apical H, K-ATPase, or proton pump, that moves H+ ions out of the parietal cell against a concentration gradient of more than a million-fold. At rest, the proton pumps are sequestered within the parietal cell in a series of membrane compaments known as tubulovesicles. When the parietal cell begins to secrete, on the other hand, these vesicles fuse with invaginations of the apical membrane known as canaliculi, thereby substantially amplifying the apical membrane area and positioning the proton pumps to begin acid secretion. The apical membrane also contains potassium channels, which supply the K+ ions to be exchanged for H+, and Cl- channels that supply the counterion for HCl secretion. The secretion of protons is also accompanied by the release of equivalent numbers of bicarbonate ions into the bloodstream, are later used to neutralize gastric acidity once its function is complete.Reference: Ganong review of medical physiology 23rd edition Page no: 434