Extrahepatic bile duct does not include

Everyone has a liver, and the main function of the liver is to help us absorb toxins and excrete toxins, repeating this cycle back and forth. However, some people have liver problems, such as hepatitis or the liver absorbs too many toxins, causing liver cysts, liver edema and other diseases. Many people will find during hospital examinations that the extrahepatic bile duct is not included. We need to first have a one-sided understanding of this and choose the appropriate method of treatment.

Bile acid

Bile is formed in the liver and is an isotonic fluid composed of bile acids, electrolytes, bilirubin, cholesterol, and phospholipids. Bile flow is achieved by active transport of bile salts and electrolytes accompanied by passive transport of water.

The liver can synthesize water-soluble bile acids from water-insoluble cholesterol, but the exact mechanism is not fully understood. Cholic acid and chenodeoxycholic acid are the two main bile acids formed in the liver, with a ratio of about 2:1, accounting for 80% of the total bile acid in humans. Bile acids are ultimately conjugated to glycine and taurine in liver cells and excreted in bile.

Bile flows from the intrahepatic collecting duct system into the proximal hepatic duct and the common hepatic duct. Under fasting conditions, approximately 50% of bile flows into the gallbladder through the cystic duct, and the remainder flows directly into the distal bile duct or common bile duct. 90% of the water in the bile in the gallbladder is absorbed as an electrolyte solution mainly through the intracellular pathway of the gallbladder mucosa, while the bile remaining in the gallbladder is a concentrated solution mainly containing bile acid and sodium.

During fasting, bile acids are concentrated in the gallbladder, and the liver secretes very little bile acid, which is dependent on bile flow. When food enters the duodenum, a series of neurohumoral mechanisms are triggered. The duodenal mucosa releases cholecystokinin and some other gastrointestinal hormone peptides (such as gastrin-releasing peptide). Cholecystokinin stimulates gallbladder contraction and bile duct sphincter relaxation. After bile flows into the duodenum and mixes with food, it performs the following functions:

(1) Bile salts can promote the dissolution of cholesterol, fat and fat-soluble vitamins in food, so as to promote their absorption in the form of mixed micelles;

(2) After bile acid enters the colon, it can induce the colon to secrete water and promote defecation;

(3) Bilirubin, a heme degradation product of aging red blood cells, can be excreted with bile;

(4) Drugs, ions, and some endogenous compounds are secreted by the liver into bile and then excreted from the body;

(5) Bile also secretes a variety of proteins that play an important role in gastrointestinal function.

Food entering the duodenum can stimulate the contraction of the gallbladder and cause it to release most of the bile acid in the stored bile pool (about 3 to 4 g in total) into the small intestine. Bile acids are rarely absorbed by passive diffusion in the proximal small intestine, but most of them reach the distal ileum, where 90% are absorbed into the portal system by active transport. The liver efficiently takes up the reabsorbed bile salt components and rapidly converts them before secreting them into bile.

Bile acids undergo enterohepatic circulation 10 to 12 times a day. During each enterohepatic cycle, a small amount of primary bile acids reaches the colon and is converted into secondary bile acids by anaerobic bacteria containing 7α-hydroxylase. Bile acid can be converted into deoxycholic acid, most of which is reabsorbed and then combined with glycine and taurine in the liver. Conjugated chenodeoxycholic acid is also converted into a secondary bile acid, lithocholic acid, in the colon. Some of this insoluble secondary bile acid is absorbed, and the rest is excreted in the feces.