What is the digestive function of each digestive tract that has a role in digesting food?

The digestion of food begins in the oral cavity, and the digestion of food in the oral cavity is mainly mechanical (food is ground), because the food stays in the oral cavity for a short time, so the digestion in the oral cavity does not play a big role.

After the food enters the stomach from the esophagus, it is subjected to the mechanical digestion of the gastric wall muscles and the chemical digestion of gastric juice, at this time, the protein in the food is initially decomposed by pepsin in the gastric juice (with the participation of gastric acid), and the gastric contents become a porridge-like chyme state, which is pushed to the duodenum through the pylorus many times in small quantities. After the chyme enters the duodenum from the stomach, it begins digestion in the small intestine.

The small intestine is the main site of digestion and absorption. Food is chemically digested in the small intestine by pancreatic juice, bile and intestinal fluid, as well as mechanical digestion by the small intestine, and various nutrients are gradually broken down into simple absorbable small molecules that are absorbed in the small intestine. As a result, after food passes through the small intestine, the digestion process is almost complete, leaving only the indigestible food residues, which enter the large intestine from the small intestine.

There is no digestion in the large intestine, and it only has a certain absorption function, absorbing a small amount of water, inorganic salts and some vitamins.

Approximate (chemical) digestion and absorption of starches, proteins, fats

Starch: Initially digested into maltose by saliva in the mouth. In the small intestine, it is digested into glucose by intestinal and pancreatic juices. All are absorbed by capillaries.

Protein: It is initially digested into peptone by gastric juice in the stomach and into amino acids by intestinal juice and pancreatic juice in the small intestine. All are absorbed by capillaries.

Fats: Digested in the small intestine by intestinal and pancreatic juices (bile facilitates digestion) are: glycerol and fatty acids, most of which are absorbed by capillaries, and a small part by capillaries.

The stomach is decomposed, just like a tooth is broken, but further,,, small intestine is digested and absorbed...

Digestion is the process in which the body decomposes large foods with complex molecular structures into small molecule chemicals that can be absorbed and have simple molecular structures through the movement of the digestive tract and the enzymatic hydrolysis of digestive gland secretions. Among them, through mechanical action, the food is changed from large pieces to small pieces, which is called mechanical digestion; Through the action of digestive enzymes, large molecules are turned into small molecules, which is called chemical digestion. Digestion facilitates the absorption of nutrients into the bloodstream and lymph through the epithelial cells of the mucosa of the digestive tract, thus providing energy for the vital activities of the body.

The digestion process includes mechanical digestion and chemical digestion, the former refers to the contraction and relaxation of the muscles of the digestive tube wall (such as oral chewing, stomach and intestinal peristalsis, etc.) to grind large pieces of food; The latter refers to the hydrolysis of foods with complex molecular structures into nutrients with simple molecular structures by various digestive enzymes, such as the hydrolysis of proteins into amino acids, the hydrolysis of fats into fatty acids and glycerol, and the hydrolysis of polysaccharides into glucose. Digestion can be divided into intracellular digestion and extracellular digestion. The food ingested by unicellular animals such as paramecium is broken down by various hydrolytic enzymes inside the cell, known as intracellular digestion.

Food of multicellular animals is ingested by the mouth end of the digestive tube and digested in the digestive tube, which is called extracellular digestion. Extracellular digestion can digest large quantities of food with a more complex chemical composition and is therefore more efficient. However, even in higher animals (e.g., humans), intracellular digestion is still partially preserved, such as white blood cells engulfing foreign bodies in the body and dissolving them in cells.

Digestion is divided into extracellular digestion and intracellular digestion.