In human anatomy, the ureters are the ducts that carry urine from the kidneys to the urinary bladder. The ureters are muscular tubes that can propel urine along by the motions of peristalsis. In the adult, the ureters are usually 25 to 35cm long.
In humans, the ureters enter the bladder posteriorly, running within the wall of the bladder for a few centimetres. There are no valves in the ureters, backflow being prevented by pressure from the filling of the bladder, as well as the tone of the muscle in the bladder wall.
The epithelial cells of the ureter are stratified (in many layers), are normally round in shape but become squamous (flat) when streched. The lamina propria is thick and elastic (as it is important that it is impermeable).
There are two spiral layers of smooth muscle in the ureter wall, an inner loose spiral, and an outer tight spiral. The inner loose spiral is sometimes described as longitudinal, and the outer as circular, (this is the opposite to the situation in the gastrointestinal tract).
The adventitia of the ureter, like elsewhere is composed of fibrous connective tissue, that binds it to adjacent tissues.
