Science
How do the kidneys work?
The kidneys work as the body's filters, cleaning waste and extra water from your blood to make urine. They constantly process your entire blood supply, keeping the balance of water, salts, and minerals just right.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how the kidneys works.
Step by step
- 1Two bean-shaped organs filter all your blood many times a day.
- 2Each holds about a million tiny filters called nephrons.
- 3They remove waste and excess water as urine.
- 4They reclaim useful substances like glucose and salts back into the blood.
- 5They also help control blood pressure and red blood cell production.
Frequently asked questions
- What do the kidneys filter out?
- Waste products like urea, plus excess water, salts, and acids, which leave the body as urine while useful substances are kept.
- How much blood do the kidneys filter?
- They process your entire blood supply many times daily — filtering roughly 180 liters of fluid, almost all of it reabsorbed.
- What happens if the kidneys fail?
- Waste and fluid build up dangerously, so people may need dialysis (machine filtering) or a kidney transplant to survive.