Bile: Bile is a yellow-green fluid that is made by the liver, stored in the gallbladder and passes through the common bile duct into the duodenum where it helps digest fat. The principal components of bile are cholesterol, bile salts, and the pigment bilirubin.

An imbalance between these components of bile -- cholesterol, bile salts, and bilirubin -- leads to the formation of gallstones. Cholesterol is normally kept in liquid form by the dissolving action of the bile salts; an increased amount of cholesterol in the bile overwhelms the dissolving capacity of the bile salts and leads to the formation of cholesterol gallstones. Similarly, a deficiency of bile salts promotes cholesterol gallstone formation. Pigment gallstones are frequently associated with chronic infection in the bile, especially in certain Asian countries where parasitic infection of the bile ducts is common. Patients with blood diseases that cause excessive breakdown of red blood cells can have increased amounts of bilirubin (breakdown product of red cells) in the bile, thus causing bilirubin gallstone formation.