Umbrella cells are specialized epithelial cells found in the urinary bladder. They form the outermost layer of the bladder lining and play a crucial role in protecting the underlying tissues from urine, which can be toxic. These cells are unique because they can stretch and flatten as the bladder fills with urine, allowing the bladder to expand without losing its protective barrier. These cells are characterized by their dome-shaped appearance when the bladder is empty. As the bladder fills, umbrella cells flatten out, accommodating the increased volume. This ability to change shape is essential for maintaining bladder function and preventing leakage of urine into surrounding tissues.