The test point of this question is: the composition and function of the digestive system. The digestive system consists of digestive tract and digestive glands. The digestive tract includes mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. Structure and function of digestive tract organs;
(1) Stomach (pictured): Located in the upper left of abdominal cavity, it is the largest part of digestive tract. It can secrete hydrochloric acid and pepsin. It has a preliminary digestion effect on protein, but has no effect on starch digestion.
(2) Small intestine: The small intestine is coiled in the abdominal cavity, about 5-6 meters long, and the first section is called duodenum. The small intestine is the longest section of the digestive tract, and it is the main place for digesting food and absorbing nutrition. There are many annular folds on the surface of small intestinal mucosa, and there are many villous protrusions on the folds-small intestinal villi (pictured). Mucosal depressions between villi of small intestine form intestinal glands, which can secrete intestinal juice to digest food. The folds and villi on the inner surface of the small intestine greatly increase the area for digesting food and absorbing nutrients.
(3) Large intestine: The first section of the large intestine is called cecum. There is a tiny protrusion on the cecum called appendix, and the intestine is located at the lower right of the abdominal cavity, so when you suffer from appendicitis, the lower right abdomen will hurt. The large intestine has no digestion ability, but its absorption ability is weak, and it can absorb a small amount of water, inorganic salts and some vitamins.
(4) Liver: The liver is the largest gland in the human body. The liver can secrete bile and store it in the gallbladder. When food enters the mouth, stomach and small intestine, it can reflexively cause gallbladder contraction, and bile flows into the duodenum through the common bile duct. There is no digestive enzyme in bile, and its function is to emulsify fat into fine particles, increase the contact area between fat and pancreatic lipase, which is beneficial to the digestion and absorption of fat.