Urothelium is a specialized type of epithelial tissue that lines the urinary bladder and parts of the urinary tract, including the ureters and urethra. It is designed to stretch and accommodate varying volumes of urine, providing a barrier to protect underlying tissues from toxins and pathogens. This tissue is unique because it can change shape, transitioning from a relaxed state to a stretched state as the bladder fills. Urothelium consists of several layers of cells, including umbrella cells on the surface, which help prevent the passage of urine components into the bloodstream.