Urothelial cells

Urothelial cells (transitional epithelial cells) line the urinary tract from renal pelvis to urethra. They form a distensible, impermeable barrier. The superficial umbrella cells have a unique apical plaque of uroplakin proteins and can change shape (from cuboidal to squamous) as the bladder fills and stretches, preventing urine from leaking into underlying tissues. This epithelium also protects against toxic substances in urine.