Bladder epithelium. Light micrograph of a vertical section through the wall of the urinary bladder. The inner surface is at top. The upper layer (light pink) is the transitional epithelium, which is especially adapted for the bladder's function of containing urine. The plasma membranes surrounding the epithelial cells here are much thicker than most cell membranes, with a specialised sub-structure. The epithelium is thus rendered impermeable to potentially toxic urine. Below the epithelium is smooth muscle and connective tissue (dark red). Magnification: x3300 when printed 10 centimetres wide.