The urinary bladder is a hollow, spherical-shaped muscular organ that stores urine from kidneys and helps to expel urine out of the body. This distensible (or elastic) organ rests at the base of the pelvis superior to the reproductive organs of the pelvis. The inner surface of the urinary bladder lines many tiny wrinkles (known as rugae) which allow the bladder to stretch as it fills with urine. The urinary bladder is composed of three distinct tissue layers: the innermost mucosa layer (lined with transitional epithelial tissue), the submucosa layer with connective tissue, and the outermost muscularis layer. Elastic fibers, transitional epithelium, and visceral muscle tissue in the walls of the urinary bladder contribute to its elasticity and distensibility, allowing it to easily regulate its size to accommodate urine. Common disorders associated with the bladder tissue include cystitis, urinary stones, and bladder cancer. A variety of target molecules on bladder tissue are used to detect the related diseases.