The gallbladder is an 8cm sac that is stuck to the undersurface of the liver. Its function is to store and concentrate the bile that the liver makes and to deliver it to the gut (duodenum and small intestine) when you eat. The bile enters the gut through the common bile duct - this shares an opening with the pancreatic duct. The bile mixes with the food and aids in the absorption of fats and certain vitamins that are dissolved in the fats.