Gallstones are the formation of small hard masses in the gallbladder or the common bile duct. These masses form from precipitation of molecules out of bile, the digestive fluid secreted by the gall bladder. Gallstones prove quite common, affecting 20 percent of people over the age of 65, according to the online medical library Merck Manuals. A person suffering chronic pain due to gallstones often has the gallbladder removed. There are several different types of gallstones, which differ based on their composition.
Cholesterol Gallstones
Gallstones made out of cholesterol remain the most common type of gallstone in the Western world due to prevalence of high fat diets, according to Merck Manuals. The National Institute of Diabetes and Digestive and Kidney Diseases or NIDDK specifies that approximately 80 percent of people with this condition in the U.S. have cholesterol gallstones. These stones usually appear yellow-green in color. The formation of gallstones involves cholesterol secreted by the liver that mixes with bile produced by the gallbladder. Cholesterol is usually dissolved in bile; however, if bile becomes over saturated with cholesterol, it will precipitate out, forming hard stones. The precipitated molecules start out as small crystals; as more and more of them form, they clump together forming a larger and larger gallstone.
Pigment Gallstones
Another type of molecule that precipitates out of bile to form gallstones is bilirubinate, which is the predominant color-producing pigment in the bile fluid. Bilirubinate causes these gallstones to appear brown in color, according to the University of Maryland Medical Center. In fact, bilirubinate causes the brown/yellow color of stool. Merck Manuals adds that bacterial infections can contribute to gallstone formation by causing inflammation and reducing the flow of bile through the bile duct. Pigment gallstones that form during a bacterial infection actually have a very dark brown or black color.
Calcium Gallstones
Though less common than cholesterol or pigment gallstones, Merck Manuals states that stones in the gall bladder or bile duct can also consist of calcium. The Genentech website reports that an antibiotic that they manufacture, ceftriaxone, can combine with calcium in bile, and cause the production of gallstones. However, Genentech states that types of gallstones generally disappear after discontinuing use of the antibiotic.
