Ureters

The ureters are muscular tubes--about 16 inches long--that attach at their upper end to the kidneys and at their lower end to the bladder.

Urine formed in the kidneys flows down the ureters into the bladder, but it does not flow passively. The ureters push each small amount of urine along in waves of contraction, at low pressure. At the bladder, each ureter passes through a sphincter, a circular muscular structure that opens to let the urine through and then closes tightly like the aperture of a camera.