Formation of the bile

: Bile is an aqueous isotonic solution of bile acids, cholesterol, phospholipids, bile pigments and inorganic electrolytes. It is secreted by the hepatocytes into the bile canaliculi and modified by the bile ducts and gallbladder. The chief mechanisms of bile formation are: 1. active transport of bile acids, responsible for the bile acid-dependent flow. This is the consequence of an osmotic flux of water and electrolytes in response to bile acid secretion. Ursodeoxycholic acid (and other bile acids) have an hypercholeretic effect, probably through a chole-hepatic circulation. 2. Transport of other compounds, responsible for the bile acid-independent flow. These compounds are incompletely identified: organic compounds (such as glutathione) or inorganic electrolytes could be involved. 3. Reabsorption of water and electrolytes in the bile ducts and in the gallbladder, and secretion of bicarbonate by the bile ducts, stimulated by secretin. Cholestasis may be extra or intrahepatic. Extrahepatic cholestasis is always due to obstruction of bile ducts. Intrahepatic cholestasis may result from obstruction of intrahepatic bile ducts or alteration of secretory mechanisms by the hepatocyte.