The ureters carry urine from the kidneys to the bladder, and are muscular tubes lined by a urothelium. They use peristaltic contractions to send the urine in the right direction so do not rely on gravity, and because they run from the mid-abdomen down to the true pelvis they receive a number of arterial branches as they travel and likewise use nerves from a number of spinal levels to send the pain of a kidney stone obstruction back to the brain.