1What's going on under the skin
Defender cells, and the pipes that carry them
You only need two ideas. Watch each one:
Tiny defender cells
Your blood is full of little guards. They hunt down germs and gobble them up. But they live inside your blood vessels — they can only help a cut if they can get out to it.
Pipes that can open up
Blood vessels are pipes that can change size. Usually they stay snug and tight. But near a hurt spot, your body can make them widen and go leaky on purpose.
2Two ways a pipe can be
The snug pipe vs the open floodgate
The blood vessel right next to a cut can be in one of two states. They look completely different:
The snug pipe
Normal width, sealed walls. Skin looks calm — but the defenders are stuck inside, racing past.
The open floodgate
Wide and leaky. Blood rushes in (that's the redness), fluid seeps out (that's the puffiness), and defenders squeeze through to the cut.
3Your turn — open the floodgate
Slide the pipe open and watch the skin change
Here's one blood vessel running under a patch of skin. Drag the slider to open it up. Watch the blood rush in, the skin go red and puffy — and the defender cells start squeezing out toward the surface.
4Now let the germs in
A real test: stop the swelling, and does the cut heal better? 🦠
This time bacteria sneak into the cut. You get one choice: keep the vessel snug so the skin stays neat, or let it go wide & leaky with all that redness and puffiness. Then watch the race. But guess first.
Guess before you run it
You stop a cut from getting red and puffy so it stays neat. Does it heal better that way?