What are the layers of the bladder?

The bladder consists of three layers of tissue. The innermost layer of the bladder which comes into contact with the urine stored inside the bladder is called the "mucosa" and consists of several layers of specialized cells called "transitional cells," which are almost exclusively found in the urinary system of the body. These same cells also form the inner lining of the ureters, kidneys, and a part of the urethra. These cells form a waterproof lining within these organs to prevent the urine from going into the deeper tissue layers.

The middle layer is a thin lining known as the "lamina propria" and forms the boundary between the inner "mucosa" and the outer muscular layer. This layer has a network of blood vessels and nerves and is an important landmark in terms of the staging of bladder cancer (described in detail below in the bladder cancer staging section).

The outer layer of the bladder comprises of the "detrusor" muscle and is called the "muscularis." This is the thickest layer of the bladder wall. Its main function is to relax slowly as the bladder fills up to provide low-pressure urine storage and then to contract to compress the bladder and expel the urine out during the act of passing urine. Outside these three layers is a variable amount of fat which lines and protects the bladder like a soft cushion and separates it from the surrounding organs such as the rectum and the muscles and bones of the pelvis.