Why can bile digest fat without digestive enzymes?

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The liver secretes bile. Bile does not contain digestive enzymes and is a mixture of bile salts, bile pigments and cholesterol. Its main function is the role of bile salts: emulsifying fat and promoting fat digestion; promoting the absorption of fatty acids and fat-soluble vitamins; preventing cholesterol deposition. Cholesterol deposits are one of the causes of gallstones. Bile pigments and cholesterol have little effect on digestion.

Bile salts are polar molecules with a hydrophilic hydroxyl group at one end and a lipophilic sterol compound at the other end. The fat droplets in the intestine are surrounded by bile salt molecules. The lipophilic end of the bile salt molecules Binds to lipid molecules, while the hydrophilic end is exposed to the aqueous solution in the intestine. In this way, the fat droplets are isolated from each other and do not merge into large groups, forming water-soluble droplets. This is the emulsification of bile, that is, the role of bile salts in digesting fat.

The small intestine cannot digest fat. After the fat is emulsified, part of it is decomposed into glycerol and fatty acids through the action of lipase and absorbed by the intestinal wall cells. The rest is not digested, or only one or two fatty acids are shed and become diglycerides or monoglycerides. The fatty acids produced by digestion are also polar molecules, and they can also combine with fats, monoglycerides and diglycerides to form small water-soluble pellets. These small pellets can continue to be digested or can enter cells directly through endocytosis (pinocytosis) of intestinal wall cells. In the cells, glycerol and fatty acids are combined to form fats. These fats and the fats that enter the cells directly enter the lymphatic vessels (milk ducts) in the intestines and are transported away. Glycerol, fatty acids and short-chain fat molecules can also enter blood vessels and be transported away.

Hope this helps.