The bladder

The bladder is part of the urinary system. It is a hollow organ in the pelvis that stores urine (pee) before it leaves the body. The wall of the bladder is stretchy so it gets bigger (expands) as it fills with urine and gets smaller (contracts) as it empties.

How the bladder works

Urine is made by the kidneys and travels to the bladder along 2 long tubes called ureters. When the bladder is full of urine, muscles in the bladder wall tighten and push the urine out of the bladder through the urethra where it leaves the body.

Layers of the bladder wall

The bladder wall is made up of 3 main layers.

The urothelium is the inner lining of the bladder. It is made up of urothelial cells (also called transitional cells). The urothelium is also called the transitional epithelium.

The lamina propria (also called the submucosa) is a thin layer of connective tissue that surrounds the urothelium. It contains blood vessels, nerves and glands.

The muscularis propria is the thick, outer muscle layer of the bladder. It is made up of 3 layers of muscle that work automatically without you thinking about it (called smooth muscle).

Other tissue that separates the bladder from other organs are:

• serosa – a thin membrane that covers the top part of the bladder
• adventitia – loose connective tissue that covers areas of the bladder where there is no serosa
• perivesical fat – a layer of fat surrounding the bladder