How the urinary system works

The bladder is part of the urinary tract – the system that removes liquid waste from the body. The urinary tract is made up of 2 kidneys, 2 ureters, the bladder, and the urethra. Urine is made in the kidneys. It flows through the ureters to the bladder for storage. It passes out of the body through the urethra. You can live without a bladder, but you must have a certain amount of kidney function to grow and be healthy.

Illustration showing a normal urinary system including locations of the kidneys, ureter, bladder and urethra

Kidneys: The kidneys are a pair of bean-shaped organs, each about the size of a fist. They are fixed to the upper back wall of the abdominal cavity. One kidney is just to the left and the other just to the right of the spine. Both are protected by the lower ribcage. Their main job is to filter the blood to remove excess water, salt, and waste products – these become urine. They also help make sure the body has enough red blood cells by making a hormone that tells the bone marrow to make more red blood cells.

Ureters: The 2 ureters are 10- to 12-inch long tubes that connect the kidneys to the bladder. They take away urine as it’s made by kidneys. The ureters have muscles that squeeze the urine down through the ureters and into the bladder.

Bladder: The bladder is a hollow organ with flexible, muscular walls that stores urine. The average adult bladder holds about 2 cups of urine. Every so often, the person releases urine to empty the bladder.

Urethra: The urethra is the tube that drains urine from the bladder to outside of the body.

In its original form this document was written by the United Ostomy Association, Inc. (1962-2005) and reviewed by Jan Clark, RNET, CWOCN and Peg Grover, RNET. It has since been modified and updated by:

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: December 2, 2014 Last Revised: December 2, 2014

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