The gallbladder is an organ that normally functions to store bile excreted from the liver. Bile is a solution composed of water, bile salts, lecithin, cholesterol and some other small solutes. Changes in the relative concentration of these components may cause precipitation from solution and formation of a nidus, or nest, around which gallstones are formed. Gallstones can become large and block the opening from the gallbladder or cystic duct. This produces pain in the right upper quadrant or midepigastrum (above the belly button) in the abdomen that feels like cramping.