The stomach digests food by means of mechanical and chemical digestion.
1. Mechanical digestion: food enters the mouth and is mechanically digested by chewing and then mixed with saliva, which is initially broken down by salivary amylase. Food enters the stomach through the esophagus and is mechanically digested by peristalsis and grinding of the stomach wall muscles.
2. Chemical digestion: food and gastric juice are fully mixed, in which gastric acid and pepsin carry out chemical digestion of food, and the stomach contents become coeliac. Through gastric peristalsis, the chyme enters the small intestine through the duodenum for further digestion and absorption. In the small intestine, various nutrients are gradually broken down into simple absorbable small molecules, while the indigestible food residue enters the large intestine and is then excreted through the anus.