At the base of the oxyntic gland, in addition to the parietal cells, the chief cells (peptic cells) are located, mainly in the lower half of the gastric glands, these cells have large basophilic zymogen granules, more prominent in the apical region and responsible of the secretion of pepsinogen proteolytic enzymes, a relatively constant fraction of pepsinogen I released by the chief cells is absorbed by the blood instead of passing into the gastric lumen. The stomach acid transforms pepsinogen into pepsin, which breaks down proteins in food during digestion.
