Answer
Parietal cells of gastric glands produce the enzyme, carbonic anhydrase (CAH). CAH catalyses the following reaction:
CO2+H2O--CAH>H2CO3>HCO3+H+
Carbon dioxide +water plus carbonic anhydrase gives Carbonic acid which dissociates into bicarbonate anions and hydrogen cations.
Work Step by Step
After these reactions have taken place, parietal cells pump the H+ cations into the lumen of the gastric glands ; this is effected by an active protein transport process ( H+/K+ATPase) that uses the energy of ATP to pump K+ cations out, and H+ protons into the cells. H+ cations are pumped out of the parietal cells as quickly as they produced. Regarding the bicarbonate ions, they are exchanged for chloride ions from blood plasma in a process known as " the chloride shift".
Hydrochloric acid is produced when the H+ cations pumped into the gland lumen by the parietal cells link up with the CL- anions from the blood ( H+plus CL- >HCL.). Consequently, HCL accumulates in the stomach, while bicarbonate ions (HCo3-) accumulate in the blood leaving the stomach
Hydrochloric acid is a strong acid and the pH of gastric juice may fall below 1.0. One of the main functions of stomach acid is to convert the inactive zymogen , pepsinogen, into the active proteolytic enzyme pepsin . Other functions of stomach acid are as follows : it helps to liquify connective tissue and plant cell walls; it converts ingested ferric ions (Fe+++) into more easily absorbed ferrous ions (Fe++) used in hemoglobin synthesis ) it helps to form chyme, and it destroys most pathogens that enter the stomach.
