In the presence of peptides within the stomach, the gastrin hormone is released into the bloodstream. This hormone stimulates the gastric glands to supply digestive juice. Digestive juice is an acid juice (pH 1 - 3). HCl (Hydrochloric Acid) keeps the stomach pH acidic. As HCl may be a strong acid, it'll kill most of the bacteria present within the food. The opposite primary function is to convert pepsinogen into pepsin.