Food is forced by peristaltic action through the œsophagus into the cardiac portion of the stomach, where it comes in contact with the gastric juice. The gastric juice is a fluid which contains hydrochloric acid (HC1) and two ferments, pepsin and rennin. The flow of gastric juice is intermittent, but about the same quantity is secreted, daily, as of saliva.
Pepsin acts upon proteid foods, changing some to albumoses and peptones, while by far the largest part is simply swollen in gastric digestion. Pepsin is the principal ferment which acts upon gelatin. Rennin is a milk-curdling ferment.
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Cut showing the division of the stomach into two portions.
The digestion of starch continues for about one-half hour after entering the stomach; by that time the food material is sufficiently mixed with the gastric juice to render the whole acid, thus destroying the alkaline reaction. Fats are set free, and to some extent melted in the stomach. About six per cent of proteids, twenty percent of sugar, and some salts are absorbed through the walls of the stomach. Water passes on with the partially digested food. If the food is liquid, the water leaves the stomach very quickly, and in drinking water some leaves the stomach before the last swallow is taken.
