Urethra. Coloured light micrograph of a section through a penis, showing the urethra. The urethra is the tube that carries urine from the bladder out of the body. The central lumen (white) carries the urine. It is covered in stratified squamous epithelial cells (orange), which are flat and scale-like in structure. Surrounding this is a supporting layer of connective tissue (grey), the lamina propria, which is rich in elastin fibres. Mucous glands (yellow) are also seen. Mucus protects the epithelium from the corrosive urine. There are also two layers of muscle tissue (not seen), which contract to expel the urine.