Ureter. Artwork showing the ureter (brown), the tube that carries urine from a kidney to the bladder (red, bottom). The structure of the ureter is seen in cross-section (centre left). The central lumen carries the urine. It is covered in transitional epithelium (dark pink), which is impervious to urine. Next is the submucosa, a layer of connective tissue that contains blood vessels (red and blue). Within the submucosa are 2 layers of muscle, longitudinal (red, inner) and circular (red, outer) which contract to push the urine along the ureter and prevent backflow. The outer membrane, the adventitia (yellow) is composed of fibrous connective tissue.