The urinary tract is composed of four parts:

1. the kidneys which produce the urine by removing water from the blood
2. the ureters which are tubes connecting the kidneys to the bladder
3. the bladder which stores the urine in the body
4. the urethra, the tube which carries the urine out of the bladder.

The bladder is a hollow balloon-shaped organ. Its walls are made of muscle. The walls of the urethra are surrounded by muscles which squeeze to keep the urethra closed and hold the urine in.