Gallstones are small hard masses that can form in the liver and the gallbladder. Gallstones themselves cause no symptoms, but they can lodge in one of the many ducts involved in the transportation of bile. When this happens, they cause inflammation and bile to accumulate in the biliary system, leading to abdominal pain.
Gallstones and Bile
Gallstones are made from components of a substance called bile. Bile, according to the American Gastroenterological Association, is a compound that is made by the liver and stored in the gallbladder. Bile is designed to help break up fats and oils in the digestive tract, which allows them to be absorbed more easily. Bile contains some salts (called bile salts), cholesterol and the proteins bilirubin and lecithin.
Solubility
The formation of bile stones is due to a chemical property of mixtures called solubility. Solubility describes the maximum concentration of a substance (called the solute) that can stay dissolved in a liquid (the solvent). When the amount of solute in a solvent exceeds the solubility, some of the solute will become un-dissolved. In the case of bile, this causes the formation of gallstones.
Types
There are two main types of gallstones, according to the National Institute of Diabetes and Digestive and Kidney Disorders (NIDDK). The most common kind of gallstone is made up of cholesterol and is yellow-green in color. Other gallstones are called pigment stones because they have a darker color. Pigment stones are mostly composed of bilirubin.
Causes
Gallstones are caused when the liver makes too much bile or when the components in bile become imbalanced, the NIDDK notes. Cholesterol stones can be the result of excess cholesterol in the bile, or they can result from the gallbladder not emptying fully during a fatty meal. What causes this to occur, however, is not known. Pigment stones primarily occur in patients with liver problems (such as cirrhosis) or those who have anemia. These disorders cause the liver to make excessive amounts of bilirubin, which can then form crystals.
Biliary Sludge
Biliary sludge, according to the Merck Manual, is the result of microscopic crystals of cholesterol, bilirubin and bile salts in the bile. These crystals are too small to be termed gallstones, though they can eventually bind together to form larger crystals and stones. The Merck Manual explains that biliary sludge can form when bile remains in the gallbladder for an extended period of time, which commonly occurs during pregnancy. If the sludge does not form gallstones, it is eliminated during the next full emptying of the gallbladder.
