The bladder is a hollow organ in the lower abdomen. It’s simply a storage place for urine, the liquid waste that’s produced by the kidneys. Urine flows from each kidney through a tube called a ureter. The ureter empties urine into the bladder. The urine stays in the bladder until you urinate.
An outer layer of muscle surrounds the inner lining of the bladder. When the bladder is full, the muscles in the bladder wall tighten to allow urination. Urine leaves the bladder through another tube, the urethra. After you urinate, the bladder shrinks in size.
The bladder consists of several layers:
The layer of cells that lines the inside of the kidneys, ureters, bladder, and urethra is called the urothelium or transitional epithelium. Cells that make up this layer are called urothelial cells or transitional cells.
The next layer down, under the urothelium, is the lamina propria. It’s a type of connective tissue.
The next layer down, under the lamina propria, is the muscularis propria. It is muscle tissue.
The next layer down is a layer of fatty connective tissue that separates the bladder from other organs.
Superficial bladder cancer affects only the lining of the bladder, the transitional epithelium. Invasive bladder cancer goes into deeper layers.