A ureter is a muscular tube carrying urine from a kidney's collecting region to the urinary bladder. Coordinated contractions of its smooth muscle propel urine along the tube, so transport is not simply a consequence of gravity.[ref]
It should be distinguished from the urethra, which carries urine outward from the bladder. The distinction separates two different transport segments and explains why a description of blockage or flow must specify its location. Urine production in the kidney, passage through the ureter and storage in the bladder are different stages of the urinary system.
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