How is bile produced and excreted?

Human liver cells secrete a liquid, which is called bile. Under normal circumstances, the human body will continuously secrete bile. Bile plays a very important role in the human body. For example, it will be discharged into the duodenum, which can promote the digestion and decomposition of fat. In addition, some bile will be directly discharged from the body. It is a very complicated process. The following will introduce the production and excretion of bile.

Production and excretion of bile:

Liver cells produce bile

Normal state: Hepatocyte bile → left and right hepatic ducts → common hepatic duct → cystic duct → gallbladder

Eating state: Gallbladder contracts, gallbladder bile → cystic duct → common bile duct → hepatopancreatic ampulla → duodenal papilla → duodenal cavity

Bile is secreted by the hepatocytes of the liver and then drained from the bile ducts between the hepatocytes to the left and right hepatic ducts, the common hepatic duct, and the cystic duct before being stored in the gallbladder. The bile is then concentrated. When the human body eats fat and other lipid substances, the bile comes out of the cystic duct and merges with the common hepatic duct to form the common bile duct. The common bile duct then merges with the pancreatic duct to form the pancreatic ampulla, which opens at the duodenal papilla. The bile enters the duodenum and then the small intestine. Bile can emulsify fat, making it easier for the human body to digest and absorb.

Hepatocytes produce bile. Normal state: Hepatocyte bile → Left and right hepatic ducts → Common hepatic duct → Cystic duct → Gallbladder. Eating state: Gallbladder contracts, gallbladder bile → Cystic duct → Common bile duct → Hepatopancreatic ampulla → Major duodenal papilla → Duodenal intestinal cavity.

About 75% of bile is produced by hepatocytes and 25% by bile duct cells. The daily secretion volume for adults is about 800 to 1000 ml. Bile is a digestive fluid that emulsifies fats, but it does not contain digestive enzymes. Bile plays an important role in the digestion and absorption of fat. Bile salts, cholesterol and lecithin in bile can reduce the surface tension of fat, emulsify the fat into many droplets, and facilitate the digestion of fat. Bile salts can also combine with fatty acid monoglycerides to form water-soluble complexes, promote the absorption of fat digestion products, and promote the absorption of fat-soluble vitamins. Bile is stored in the gallbladder during non-digestive periods. During digestion, bile is secreted in large quantities directly from the liver and from the gall bladder into the duodenum.

In addition to water and inorganic components such as sodium, potassium, calcium, and bicarbonate, bile also contains organic components such as bile pigments, bile salts, cholesterol, lecithin, fatty acids, phosphatidylcholine, and mucin. There are no digestive enzymes in bile, but bile plays an important role in the digestion and absorption of fat. The bile pigments in bile are the decomposition products of hemoglobin, mainly bilirubin, and its oxide is biliverdin. The type and concentration of bile pigments determine the color of bile.

The action of bile is mainly due to the action of bile salts. Bile salts, cholesterol and lecithin can reduce the surface tension of fat and emulsify the fat into many droplets, thereby increasing the action area of ​​pancreatic lipase and facilitating the digestion of fat; bile salts can combine with fatty acid monoglycerides to form water-soluble complexes, promoting the absorption of fat digestion products. It can also promote the absorption of fat-soluble vitamins (vitamin A, D, E, K).