What does the small intestine include?

It mainly includes duodenum, jejunum and ileum. The duodenum is divided into upper part, descending part, horizontal part and ascending part. The ampulla of the upper duodenum is the most common site of duodenal ulcer.

The upper posterior wall of duodenal-jejunum curve is fixed to the posterior abdominal wall by duodenal sling, which is called Treize ligament. It is an important sign to confirm the beginning of jejunum during operation, and the small intestine is the main part of digestion and absorption. Traditional Chinese medicine believes that the function of small intestine is to receive nutrition and secrete turbid qi.

The upper end of the small intestine starts from the entrance of the stomach and ends at the ileocecal valve, which is the longest part of the digestive tract. Adults are 5-7 meters long. According to the position and shape, it is divided into three parts: duodenum, jejunum and ileum, which are the main places for food digestion and absorption. The diameter of small intestine gradually narrows down from duodenum (about 3-5cm), and the lumen of terminal ileum is only 1.0-65438+.

Extended data:

The histological characteristics of small intestine create favorable conditions for its absorption. The physiological function of small intestine is characterized by its movement, secretion, digestion and absorption, which is closely related to drug metabolism. For example, various forms of movement of small intestine smooth muscle can complete mechanical digestion of chyme such as grinding, mixing and stirring.

Small intestinal juice secreted by small intestinal glands completes chemical digestion of chyme together with bile and pancreatic juice in the small intestine. There are many endocrine cells scattered in the secretion of small intestinal mucosa, which can secrete a variety of digestive tract hormones, such as secretin, cholecystokinin, gastrin, motilin, etc., and play an important role in regulating gastrointestinal movement and secretion.

Undifferentiated cells are located in the lower half of small intestine gland and scattered in other cells. Cell body is small, columnar and basophilic. Cells proliferate, differentiate and migrate upward to supplement the absorptive cells and goblet cells shed from the top of villi. The renewal cycle of villous epithelial cells is 2 ~ 4 days. It is generally believed that endocrine cells and Paneth cell are also derived from undifferentiated cells.

Baidu encyclopedia-small intestine