Urine, the waste product of the filtration, is produced in the kidney and flows through two 10 to 12 inch long tubes called the ureters, which connect the kidneys to the bladder. The ureters are about one quarter of an inch in diameter and their muscular walls contract to make waves of movement that force the urine into the bladder.
The bladder is expandable and stores the urine until it can be conveniently disposed of. It has one-way flap valves that allow unimpeded urinary flow into the bladder but prevents urine from flowing backward (vesicoureteral reflux) into the ureters and kidneys. When the bladder contracts it passes urine into a tubular structure, called the urethra, which transports the waste out of the body.