Bile is secreted by hepatocytes and excretes the metabolic products of hepatocytes. The components in bile can be divided into two categories: one is water, inorganic salts, etc. can pass freely through the hepatocyte membrane. Their concentration in bile is close to that of blood plasma; the other category is large molecules, such as bilirubin, bile acids, cholesterol, proteins, lecithin, fatty acids and other substances that are not originally water-soluble and need to undergo a binding process in the hepatocytes to become water-soluble before they can be discharged into the capillary bile ducts through the cytosol of hepatocytes. The daily secretion of bile can be as much as 1000ml. Clinically, the bile drained by T-tube is about 300ml to 700ml per day. Regardless of the cause of biliary obstruction, the amount of bile secretion beyond this pressure will gradually decrease with the increase of pressure. Bile secretion will stop when the pressure reaches 300mmH2O. After 48 hours of complete bile duct obstruction, the liver stops secreting bile into the bile duct, but the function of bile secretion by hepatocytes still exists. The bilirubin passes through the liver cells and then returns to the blood circulation, and the patient develops skin sclera and yellow stain. Normal adult liver bile is yellowish brown, clear and clarified, alkaline, and contains less solids, while gallbladder bile contains more solids, is neutral or weakly acidic, and its color is darkened by concentration. In addition to a large amount of water, the organic components of liver bile are mainly bile salts, cholesterol, bile pigments, phospholipids, proteins and mucus, which account for more than 60% of the total solids in bile, and the inorganic components are mainly sodium, potassium, calcium, chloride, bicarbonate and a small amount of heavy metal ions, such as copper, aluminum, zinc and manganese. The main functions of bile are as follows: (1) promote the digestion and absorption of fat, bile salts can emulsify fat, reduce the surface tension of fat, make fat droplets become finer and dispersed in aqueous solution, which can increase the area of action of lipase. In addition, bile salt has the effect of activating pancreatic lipase, which promotes and accelerates the decomposition of fat; (2) Promotes the absorption of fat-soluble vitamins A, D, E and K. The lack of bile in the intestine during biliary obstruction can lead to a lack of these vitamins in the human body, so patients with obstructive jaundice should be properly supplemented with the above vitamins before surgery. (3) Bile has the function of promoting the absorption of iron and calcium in the gastrointestinal tract, preventing the occurrence of bile deficiency anemia; (4) Bile is the most effective cholagogue, after bile enters the intestine, bile salts are absorbed and brought to the liver through the blood, and the absorbed bile salts can stimulate the liver cells to make new bile salts and promote the secretion of bile; (5) Bile has the function of inhibiting the growth of abnormal flora in the intestine, maintaining the mutual constraint of normal flora in the intestine (6) Bile pH is 7.4, which is a weak alkaline secretion and has the effect of neutralizing gastric acid, avoiding the excessive stimulation of gastric acid on gastrointestinal mucosa and preventing the occurrence of gastric and duodenal ulcers. In addition, bile can activate pancreatic proteogenic enzymes and convert into pancreatic protease to promote the digestion and absorption of protein.