How much urine?
Kidneys filter a huge amount of liquid. Very little of it leaves as urine. Liquid is measured in litres, written L.
Step 1 of 3
- Both kidneys together filter about 180 L a day.
- Most of it is taken back into the blood.
- Just 1 to 2 L leaves as urine.
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Slide the water in the body. Watch the urine.
The rule
Both kidneys together filter about 180 L of liquid in a day. Just 1 to 2 L leaves as urine. The rest is taken back. The amount taken back depends on the body’s water. It also depends on the wastes to remove.
Little water in the body means more is taken back. So there is less urine. Plenty of water means less is taken back. So there is more urine. This way the body keeps the water it needs.
| Alveoli | Nephrons | |
|---|---|---|
| Where | Lungs | Kidneys |
| Built from | Thin sacs wrapped in capillaries | A capillary cluster, a cup and a coiled tube |
| Job | Swap oxygen and carbon dioxide | Filter blood and take back useful things |