Although not essential to life or health, the gallbladder is the site and source of appreciable suffering and disease in humans. With its cystic duct, the gallbladder constitutes a blind-ended, lateral extension of the common bile duct. It is roughly the size and shape of a small pear, and is adherent to the outer surface of the liver. Besides acting as a reservoir for bile, the gallbladder concentrates and otherwise alters the composition of bile.