Gall bladder, light micrograph (LM) of a section through a human gall bladder, showing the surface tissue layers. The gall bladder is a muscular sac attached to the liver that concentrates and stores liver bile. The mucosa lining is made up of columnar epithelial cells (upper layer of cells). The surface of the gall bladder is made up of tiny finger-like projections called microvilli, which increase its surface area and aid water uptake from the bile. Connective tissue is seen below the epithelial layer. Magnification: x200 when printed at 10 centimetres wide.