Collectively, these ducts are called the biliary system. Bile is a yellowish fluid produced by the liver and is made up of soap-like chemicals that keep the cholesterol in the gallbladder in liquid form. The liver can produce as much as three cups of bile in 1 day, and at any one time, the gallbladder can store up to a cup of bile. As food passes from the stomach into the small intestine, the gallbladder contracts and sends its stored bile into the intestine through the common bile duct. Once in the intestine, bile helps to digest and absorb the fats from food that has been broken down by enzymes secreted from the pancreas and the intestine.
Gallstones are clumps of solid material that form in the bile stored in the gallbladder.
There are two major types of gallstones - cholesterol stones and pigment stones. Cholesterol stones are composed primarily of cholesterol, and they account for about 80 percent of gallstones in the United States. Pigment stones, which account for other 20 percent of gallstones are composed of bile pigments such as bilirubin, and other substances such as calcium, which are found in the bile. Gallstones can vary in size. They can be as small as a grain of sand or as big as an egg.