Part of your kidney's tiny tube dips down deep into the kidney like a U. On the way down, very thin cells let water slip out.
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The kidney's tiny tube has a U-shaped part called the loop of Henle. Fluid flows down one side and back up the other.
The downhill side is lined with very thin, flat cells. They are so thin, the tube is barely wider than a blood vessel.
Deep inside your kidney, the area around the bottom of the loop is very salty. That saltiness is the secret to saving water.
These cells have lots of tiny water doors. As the fluid flows down into the salty area, water slips out through the doors.
The water goes back into your blood instead of becoming pee. That helps you stay hydrated.
Press Let water out on the 3D model and watch the water leave the downhill side.
By Operation Ouch. A fun video for kids.
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