How do the kidneys work?

Every day your kidneys squeeze about 180 litres out of your blood and quietly put 99% of it back. Two fist-sized kidneys, about 150 g each, sit against the back wall of the abdomen, the right a little lower under the liver.

Read how it works: How do the kidneys work? · The history of understanding the kidneys · More boxes on Glassbox

Chapters in this interactive model

1. Two beans at your back: Two fist-sized filters, four tubes of blood and a bag that stores the result.
2. A million tiny filters: Zoom from a kidney to one nephron, the unit that does the work.
3. A filter pushed by blood pressure: About 180 litres a day squeezed through a three-layer sieve.
4. 180 litres in, 1.5 litres out: The tubule takes back 99% of the water, all the sugar and most of the salt.
5. The body’s control centre: Kidneys steer blood pressure, water, salt, acid and even red blood cells.
6. Keeping kidneys healthy, and what goes wrong: Stones, chronic kidney disease, dialysis and transplants.