1. The small intestine is located in the abdomen, the upper end connects with the pylorus and stomach, and the lower end connects with the large intestine through the ileocecal valve, and it is the main site for food digestion and absorption.

2. The intestinal tube is 4-6 meters long and is divided into three parts: duodenum, jejunum, and ileum. Digestion is very important because after chemical digestion, food is completed in the small intestine, after the chemical digestion of pancreatic juice, bile, and intestinal juice in the small intestine, and the mechanical digestion of small intestinal movement, the digestion process is basically completed, and nutrients are absorbed by the intestinal mucosa.

The stratified structure of the intestinal tube:

The intestinal tube is composed of a single layer of cells, and the intestinal wall consists of the mucosal layer, submucosal layer, muscular layer, and serous membrane. The wall is annularly皱褶, the mucosal epithelium is villous, the epithelium at the root of the villi sinks into the lamina propria, forming tubular intestinal glands, opening between the roots of the villi. The intestinal glands are closely related to the digestive and absorptive functions of the small intestine.

The mode of movement of the small intestine:

Multi-segmental movement, peristalsis, and migrating complex movement (MMC).

The tense form of small intestinal motility mainly includes: ①Tense contraction, which is the basis for the effective operation of other movements, keeping the small intestine in a certain shape and position, and maintaining a certain pressure in the intestinal lumen, facilitating digestion and absorption. ②The function of segmental movement is to mix the chyme with digestive juices thoroughly, increase the contact between the chyme and the intestinal mucosa, promote the lymphatic回流 within the intestinal wall, and be conducive to digestion and absorption. ③Crawling, its function is to push the chyme from the distal end into a segment, thus beginning a new segmental movement.