ureter

A ureter is one of the two tubes that carry urine from a kidney down to the bladder, one ureter per kidney. It is the second station of the urine path — the kidney filters the blood and makes the urine, the ureter carries it, the bladder stores it, and the urethra is the tube it leaves the body through. The ureter and the urethra differ by two letters and by one whole station, which is why they are the urinary system's signature pair: a question settles it by naming the station on either side. If the sentence says the tube leaves the kidney, the answer is the ureter; if it says the tube leaves the body, it is the urethra. The ureters are muscular tubes, so peristalsis — not just gravity — moves the urine down them.