Medicine & Health
How do kidneys work?
The kidneys work as your body's filtration system: they clean the blood by removing waste and excess water, balance salts and fluids, and turn the waste into urine. Blood passes through about a million tiny filters in each kidney.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how the kidneys works.
Step by step
- 1Blood enters the kidneys and passes through tiny filters (nephrons).
- 2Waste and excess water become urine; useful substances are kept.
- 3They balance the body's water, salts, and acidity.
- 4They also release hormones controlling blood pressure and red blood cells.
Frequently asked questions
- 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.