One of the principal purposes of this tissue, because to its placement in the excretory system, particularly in the ureters and urinary bladder, is to be a highly efficient permeability barrier, impenetrable to water and most tiny molecules.

The urinary system contains transitional epithelium. It lines the ureters, bladder, and proximal part of the urethra organs, which are stretched or distended as urine runs through or fills them.