Bile is a complex secretion produced in the [[liver] and secreted into the duodenum via the common bile duct (CBD). Among with other secretions delivered by the CBD, it has a role in digestion, as an emulsifying agent.
Its composition includes bile acids and their salts, cholesterol, and electrolytes. It addition, it contains some highly pigmented substances, such as bilirubin, biliverdin (biliverdine), bilifuscin, biliprasin, choleprasin, bilihumin, and bilicyanin. These both have a role in the visible yellow pignentation of jaundice, and as laboratory measurements. Drugs that stimulate bile production by the liver are choleretic, while those that accelerate flow of bile into the duodenum are cholagogues.
The primary human bile acids are derived from cholesterol in the liver and usually conjugated with glycine or taurine. They include:
The secondary bile acids are further modified by bacteria in the intestine. They play an important role in the digestion and absorption of fat.
Disorders of bile secretion and flow
Bile can solidify into gallstones, which are the obstructions in cholelithiasis. They are most commonly made of cholesterol and calcium bilirubinate. Bile disorders most often manifest in gallbladder disease, which has four stages:
- Lithogenic, or a stage predisposing to gallstone formation
- Asymtomatic gallstones
- Episodic biliary colic/acute cholecystitis
- Complicated cholelithiasis
Asymptomatic gallstones may be detected by various imaging studies. Ultrasound is the best overall study when there is specific suspicion of stones; other studies may be appropriate in specific cases.
Laboratory values are normal in asymptomatic gallstones and minor biliary colic.
In acute cholecystitis, the total white blood cell count may rise, with elevations in polymorphonuclear neutrophils. In more severe diseases, there may be elevations of bilirubin and liver-associated enzymes.
The combination of increasing leukocytosis, even with antibiotic therapy, accompanied by elevations in liver function tests, is a serious prognostic sign generally calling for urgent surgery.
Treatment of gall bladder disease
In general, the preferred treatment is endoscopic or surgical, but there can be a role for drug treatment.
Ursodeoxycholic acid, a bile acid natural to bears, lowers the cholesterol content of bile, both by reducing creation of cholesterol by the liver, and by reducing the detergent effect of bile salts in the gallbladder, protecting gallbladder structures that can hold cholesterol. Reduction of cholesterol in bile may prevent the formation of stones, and reduce the size of cholesterol-containing existing stones. When the stones become small enough, they may pass through the CBD.
Removal of the gall bladder, usually by endoscopy with open surgery reserved only for special cases, is the preferred approach. There are various more or less invsive techniques that may be appropriate; see cholecystectomy.
Alternatively, endoscopic retrograde sphincterotomy, performed by a gastroenterologist, may be able to remove small stones, or reduce risk of subsequent.
- Hoffman, HN et al. (1960), "Bile Pigments of Jaundice", J. Clin. Invest. 39: 132-142, DOI:10.1172/JCI104011
- Heuman DM, et al. (Aug 2, 2006), "Cholelithiasis", eMedicine
- Corlette, MB et al., "Transient bile duct obstruction. Response of serum bilirubin and alkaline phosphatase levels in the rat", Arch Surgery