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 composed of several layers of cells, primarily umbrella cells, which are unique for their ability to expand and contract. Urothelium plays a crucial role in maintaining the integrity of the urinary system, ensuring that urine does not leak into surrounding tissues and helping to regulate the passage of substances.