Inside your spleen, blood has to squeeze through tiny gaps. The cells that make those gaps help your body find old, worn-out red blood cells.
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Your spleen is an organ about the size of your fist. It sits on the upper left side of your belly, tucked behind your ribs.
Inside it are little blood tubes called sinusoids. Their walls are made of long, thin cells lined up side by side, like the planks of a barrel. That's why they are also called stave cells.
Thin rings wrap around the outside to hold the planks together. Between the planks there are tiny slits.
To get back into the blood tubes, red blood cells must squeeze through the slits between the stave cells.
This keeps your blood full of healthy cells that can carry oxygen.
Press Squeeze through on the 3D model and watch red blood cells slip between the stave cells.
A red blood cell lasts about four months. Then your spleen helps recycle it, and your body reuses the iron.