Light micrograph of a section through the wall of a gallbladder. The interior surface (top) of the gallbladder is a mucous membrane with many folds lined with simple columnar epithelium. Beneath the mucous membrane is connective tissue and a muscular layer of smooth muscle arranged in bundles. The gallbladder stores and concentrates bile produced by the liver and secretes it into the small intestine where it helps the body to digest fat. Magnification: x400 when printed at 15cm tall.