Bile

Bile is a digestive fluid produced by the liver and essential for the emulsification and digestion of fats. It consists primarily of bile acids and bile salts, cholesterol, phospholipids, bilirubin, electrolytes, and water.

About 0.5 to 1.0 liters are produced daily in humans. Bile flows from the liver through bile ducts into the gallbladder, where it is concentrated. In response to a meal, the hormone cholecystokinin triggers gallbladder contraction and release of bile into the duodenum via the common bile duct.

The main functional role of bile is to emulsify fats. Bile salts and phospholipids form micelles that increase the surface area of fats and aid lipase action. Bile also serves as a vehicle for excreting bilirubin, cholesterol, and various waste products.

Most bile acids are reabsorbed from the ileum and returned to the liver in the enterohepatic circulation, enabling reuse. This recycling helps regulate bile acid pools and cholesterol metabolism.

Clinical relevance: gallstones form when bile becomes supersaturated with cholesterol or bilirubin, causing solid crystals. Blockage of the bile ducts can cause cholestasis, jaundice, pale stools, and dark urine.