Ever notice your pee is darker when you're thirsty? That's because of these cells. They decide how much water to save.
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Many tiny kidney tubes drain into bigger tubes called collecting ducts. This is the last stop before fluid leaves the kidney as pee.
Most cells lining these ducts are principal cells. Principal means main. They are simple block-shaped cells. Each one has a single tiny antenna on top.
Principal cells can add or remove water doors in just minutes!
When you need water, your brain sends out a hormone. The hormone tells principal cells to add more water doors.
They also help balance salt in your body.
Next time you use the bathroom, notice the color. Pale yellow usually means you drank plenty of water. Darker usually means your gatekeepers are saving water.
By Operation Ouch. A fun video for kids.
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