QS Study

Mechanism of Secretion of Gastric HCl

The parietal cells (oxyntic) contain a system of intracellular canaliculi. HCl is formed at the membrane of these canaliculi and then conducted through an opening to the lumen. Gastric Juice is the mixture of secretions from all the glands present in the stomach. It is most helpful in digestion of food. It consists of Enzymes present in the stomach. It helps in absorbing the food in the body very easily.

When acid secretion is stimulated there is a dramatic change in the morphology of the membranes of the parietal cell. Gastric HCl converts inactive pepsinogen into active pepsin. It acts as an antiseptic agent against bacteria. It hydrolyzes all food stuff.

Steps at a mechanism of HCl secretion

  • CO2 either formed during metabolism in the cell or entering the cell from blood, combines under the influence of carbonic anhydrase with H2O to form H2CO3.
  • H2CO3 is dissociated to form H+ and HCO3.
  • H+ is then actively secreted into the canaliculi in exchange for K+ catalyzed by H+ – K+ ATP ase.
  • HCO3 passes into the ECF or plasma in exchange for Cl that enters the cells from ECF and later extruded into the canaliculi down the electrochemical gradient.
  • This Cl combines with H+ to form HCl which is secreted from canaliculi into a lumen. Acid secretion is stimulated by histamine via H2 receptor and probably by gastrin via gastrin receptor in the membrane of parietal cells.