The digestive system consists of many organs, and generally speaking, it can be divided into organs within the lumen of the digestive tract, or organs outside the lumen of the digestive tract. The organs in the lumen of the digestive tract are the esophagus, stomach, small intestine, and large intestine. The small intestine is divided into duodenum, jejunum and ileum, and the large intestine is divided into appendix, cecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum. The organs outside the lumen of the digestive tract mainly include the liver, gallbladder, pancreas and so on. The main function of the digestive system is to digest and absorb food, while the extra-luminal organs of the digestive tract are mainly responsible for secreting bile, pancreatic amylase, pancreatic lipase, protease, etc. to assist in the digestion and absorption of food, thus facilitating the digestion and absorption of the gastrointestinal tract. Therefore, if a patient has symptoms of digestive system, he/she should be examined and tested according to the above mentioned organs to clarify the diagnosis.