Ureter

In human anatomy, the ureters are tubes made of smooth muscle fibers that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25–30 cm (10–12 in) long and around 3–4 mm (0.12–0.16 in) in diameter. Histologically, the ureter is lined by the urothelium, a type of transitional epithelium, and has an additional smooth muscle layer in the more distal one-third to assist with peristalsis.View of the ureter under the microscopeWall of the ureterUltrasound showing a jet of urine entering the bladder (large black section) through the ureter. In human anatomy, the ureters are tubes made of smooth muscle fibers that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25–30 cm (10–12 in) long and around 3–4 mm (0.12–0.16 in) in diameter. Histologically, the ureter is lined by the urothelium, a type of transitional epithelium, and has an additional smooth muscle layer in the more distal one-third to assist with peristalsis. In humans, the ureters arise from the pelvis of each kidney, and descend on top of the psoas major muscle to reach the brim of the pelvis. Here, they cross in front of the common iliac arteries. They then pass down along the sides of the pelvis, and finally curve forwards and enter the bladder from its left and right sides at the back of the bladder.:324–326 This is classically depicted as running 'posteroinferiorly on the lateral walls of the pelvis and then curve anteromedially to enter the bladder'. The orifices of the ureters are placed at the postero-lateral angles of the trigone of the bladder, and are usually slit-like in form. In the contracted bladder they are about 25 mm (1 in) apart and about the same distance from the internal urethral orifice; in the distended bladder these measurements may be increased to about 50 mm (2 in). The junction between the pelvis of the kidney and the ureters is known as the ureteropelvic junction or ureteral pelvic junction, and the junction between the ureter and the bladder is known as the ureterovesical (ureter-bladder) junction. At the entrance to the bladder, the ureters are surrounded by valves known as ureterovesical valves, which prevent vesicoureteral reflux (backflow of urine). In females, the ureters pass through the mesometrium and under the uterine arteries on the way to the urinary bladder.