How to distinguish upper digestive tract from lower digestive tract?

The distinction between the upper digestive tract and the lower digestive tract is artificial, and it is divided according to its different positions in the ligament of Treize. The digestive tract above this ligament is called the upper digestive tract, and the digestive tract below Treize ligament is called the lower digestive tract.

Treitz ligament, also known as duodenal suspensory ligament, has a bundle of myofibrillar cords connected to the duodenal jejunum curve from the right corner of diaphragm downward, fixing the duodenal jejunum to the posterior abdominal wall. Treitz ligament is an important sign to confirm the origin of jejunum.

Extended data

The upper digestive tract consists of mouth, pharynx, esophagus, stomach and duodenum. The lower digestive tract consists of jejunum, ileum and large intestine.

Food digestion:

The digestion of food begins in the mouth, where food is mainly digested mechanically (food is ground). Because the food stays in the mouth for a short time, the digestion in the mouth is not significant.

After food enters the stomach from the esophagus, it is mechanically digested by the muscles of the stomach wall and chemically digested by the gastric juice. At this time, protein in food is preliminarily decomposed by pepsin in gastric juice (with the participation of gastric acid), and the contents in the stomach become gruel-like chyme, which is pushed to the duodenum several times through pylorus. After chyme enters duodenum from stomach, it begins to be digested in small intestine.

Small intestine is the main place for digestion and absorption. Food is chemically digested by pancreatic juice, bile and intestinal juice and mechanically digested by small intestine, and various nutrients are gradually decomposed into simple absorbable small molecules and absorbed in small intestine. Therefore, after food passes through the small intestine, the digestion process has been basically completed, leaving only indigestible food residues, which enter the large intestine from the small intestine.

The large intestine has no digestion, but only a certain absorption function.

Reference: Baidu Encyclopedia-Digestive Tract