The gallbladder is a small sac that sits under the liver and stores bile after it is produced by the liver.
After a meal, the gallbladder contracts and empties bile through the cystic duct (tube) and bile ducts into the small intestine to help digest fats.
Gallstones are formed in the gallbladder from cholesterol and other material found in bile. A high concentration of cholesterol in bile and conditions such as pregnancy, which interfere with normal gallbladder emptying, promote gallstone formation.
Gallstones may be tiny or as large as a golf ball.