The biliary system has the functions of secretion, storage, concentration and transportation of bile, and has an important regulatory role in the discharge of bile into the duodenum. Bile production, secretion and metabolism (1) Bile production and components Normal adult hepatocytes and bile ducts secrete about 800-1200ml of bile daily, of which about 3/4 is secreted by hepatocytes. Bile is 97% water, and other components include bile acids, bile salts, cholesterol, phosphatidylcholine, bile pigments, fatty acids, enzymes, inorganic salts and stimulating factors. (2) Physiological functions of bile ① Emulsifying fat: bile salts enter the intestine and combine with fat in food to form fat particles that can be dissolved in water, which facilitates the absorption of intestinal mucosa. ②Promote the absorption of fat-soluble vitamins. Facilitate the absorption of fat, cholesterol and vitamins A, D, E and K. ③Inhibit the growth of pathogenic bacteria and endotoxin production in the intestine. ④Stimulate intestinal peristalsis. (5) Neutralize stomach acid. (3) Bile secretion The secretion of bile is regulated by neuroendocrine regulation. (4) Bile metabolism The metabolism of cholesterol, bile pigments, bile acids and phosphatidylcholine in bile and the changes in their levels are of clinical importance. The cholesterol, bile salts and phosphatidylcholine in normal bile form a microcolloid solution in a certain ratio; if the ratio of the three is out of balance, the cholesterol will precipitate easily to form a solid. Bilirubin in bile cannot be hydrolyzed into non-conjugated bilirubin, then it is easy for calcium to combine to form calcium bilirubin, which promotes the formation of bilirubin stones. Bile ducts and gallbladder physiological functions (1) Bile ducts: transport bile to the gallbladder and duodenum, capillary bile ducts play an important role in regulating bile flow and composition. (2) Gallbladder: including the functions of concentration, storage, discharge and secretion of bile.