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How the Urinary System Works

Tap an organ to see its role in the urinary system.

Kidneys

Two bean-shaped organs that filter waste products, excess water, and toxins out of the blood, while also regulating electrolyte balance and blood pressure, processing the body's entire blood supply many times a day.

Nephrons

The microscopic functional units within each kidney, numbering roughly a million per kidney, where the actual filtering of blood and formation of urine takes place.

Ureters

Two thin, muscular tubes that carry urine from each kidney down to the bladder, using wave-like muscle contractions to move urine along rather than relying on gravity alone.

Bladder

A hollow, muscular, balloon-like organ that stores urine until it is ready to be released, capable of stretching to hold a few hundred milliliters before signaling the need to urinate.

Urethra

The final tube through which urine exits the body, controlled by muscular sphincters that allow for voluntary control over when urination occurs.

Far more than a waste-disposal system

This page is for general educational information only and is not a substitute for professional medical advice. Beyond simply removing waste, the kidneys play a critical role in maintaining the body's overall chemical balance, regulating blood pressure through hormone production, and stimulating red blood cell production β€” functions that go well beyond their commonly understood role.

Frequently Asked Questions

How much blood do the kidneys actually filter each day?

The two kidneys together filter the body's entire blood volume roughly 40 times per day, processing about 180 liters of fluid daily, though the vast majority of that filtered fluid is reabsorbed and only about 1 to 2 liters is actually excreted as urine.

Can a person survive with only one kidney?

Yes β€” a single healthy kidney can generally perform enough of the necessary filtering function to maintain normal health, which is why kidney donation from a living donor is medically possible.