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How do the kidneys work?
Quick answer
The kidneys work as the body's filtration system: they continuously clean the blood, removing waste and excess water to make urine while keeping the right balance of water, salts, and minerals. Two fist-sized kidneys filter all your blood about 30 times a day.
Step by step
- Each kidney contains about a million tiny filters called nephrons.
- Nephrons filter waste and excess fluid from the blood, returning useful substances to it.
- The filtered waste and water leave as urine, which drains to the bladder.
- Kidneys also balance salts and minerals, help regulate blood pressure, and release hormones.
- They filter roughly 180 litres of blood a day, concentrating waste into about 1–2 litres of urine.
People also ask
What do the kidneys actually remove?
Metabolic waste like urea, excess water, and surplus salts and minerals — keeping the blood's composition balanced and removing toxins.
Can you live with one kidney?
Yes. A single healthy kidney can do the work of two, which is why living kidney donation is possible.
Besides filtering, what do kidneys do?
They help control blood pressure, balance the body's water and minerals, keep blood chemistry steady, and release hormones that signal the body to make red blood cells.
What do the kidneys do?
They filter waste and extra water from the blood, balance fluids and salts, and make urine.
What is a nephron?
The kidney's tiny filtering unit; each kidney has about a million of them.
Why are kidneys important?
Without filtration, waste builds up in the blood, which is dangerous — hence dialysis when kidneys fail.
Part of the guide: How Your Body Works →