Urethra. Section through the female urethra, the tube that carries urine from the bladder out of the body. At centre is the lumen, through which the urine travels. It is surrounded by a thin layer of epithelial tissue. The next layer, the largest layer seen, is a spongy erectile tissue (pink) consisting of connective tissue, muscles, blood vessels (red and blue) and mucus-secreting glands (yellow). Mucus protects the epithelium from the corrosive urine. Finally there are 2 layers of muscles, longitudinal (inner) and circular (outer) which contract to push urine out of the body.