Food enters the small intestine first and then the large intestine. After eating through the mouth, food reaches the stomach through the esophagus, where it undergoes chemical digestion by gastric acid and mechanical movement of the stomach, and reaches the small intestine after digestion. The small intestine is the most important digestive and absorption organ of the human body. It contains small intestinal fluid, pancreatic fluid and bile, which can fully digest food chemically, and with the peristaltic movement of the small intestine, the food is broken down into absorbable nutrients. The mucous membrane of small intestine is rich in blood vessels, and after the absorption of nutrients is completed, it enters the bloodstream and reaches other organs of the body through blood circulation. The remaining food residue enters the large intestine, where it absorbs a large amount of water and forms stools that are excreted through the anus. The entire digestive tract is an interconnected organ, which is precisely regulated by the neurohumoral system.