In order to better understand the occurrence of colorectal cancer, we first need to know the anatomy and function of the large intestine. Food enters through the mouth and passes through the esophagus (the muscular tube connecting the mouth and stomach), stomach, small intestine and finally into the large intestine. Each organ of the digestive tract has a special digestive function. The stomach stores and mixes food, secretes enzymes and gastric acid to start digestion of food, the small intestine is a long digestive tube that absorbs fats, proteins and carbohydrates, and the residue left after digestion in the small intestine enters the large intestine, which consists of the colon and rectum, and the large intestine absorbs water to prevent dehydration, and only a very small amount of water is excreted in the stool (solid waste). . The colon is a tubular organ in the abdominal cavity, about 1.5m long, extending from the right side of the abdomen to the left side, shaped like a “door”. The small intestine is connected to the colon in the lower right abdomen through the ileocecal collaterals. The appendix protrudes from the ileocecal junction like an earthworm. Large intestine The large intestine starts from the right side and passes through five parts: right hemicocele, transverse colon, descending colon, sigmoid colon (the S-row segment of the upper rectum), and rectum. The blood at the beginning of the colon is supplied by the large arteries from the heart, which are called mesenteric vessels, and many smaller vessels from the large vessels to supply the small intestine and large intestine. These lymph nodes are part of the immune system and play an important role in fighting colon cancer. Having said that, one may ask why is it important to understand the anatomy of the colon? When a tumor occurs in the colon, is it enough to remove it? The answer is simple: colon cancer needs to know its location and the segment of the intestine invaded by the tumor in order to decide the scope of surgical resection. Only when we know where the tumor is growing can we know the correct surgical approach. In addition, cancer invading different levels of the colon will affect the prognosis of the disease and the possibility of recurrence. Therefore, it is important to master these details if you want to prolong your survival. The structure of the colon consists of 4 layers: mucosal layer, submucosal layer, muscular layer and plasma layer. The mucosal layer is the innermost layer of the colon and contains glandular cells that absorb water and secrete mucus into the intestinal lumen. The mucosa is shiny, smooth and moist, just like the oral cavity, and is made up of millions of cells arranged in the colon, which can develop into polyps and tumors when there is abnormal growth of mucosal tissue. The submucosa is the fibrous submucosa, which contains microvascular and lymphatic vessels supplying the colon, followed by the muscularis, which pushes the colon contents into the rectum, and the outermost layer is the plasma layer.