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Every breath
This is the inside of your windpipe.
Every breath you take comes down this way.
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What air is for
Air comes in here to bring you oxygen.
Every part of you needs it, all day and all night.
And the same air carries out carbon dioxide, the waste your body makes.
In, then out. About twenty thousand times a day, without you thinking about it.
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Held open
The firm rings around you are cartilage.
It is the same springy stuff as the tip of your nose.
They hold this passage open, so a breath always has room to get through.
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The tiny hairs
Look at the surface. It is covered in tiny hairs.
They are called cilia, and they never stop moving.
They sweep upwards, like a brush, carrying dust and germs back towards your throat.
You swallow it without noticing. That is how this passage keeps itself clean.
They line the whole way down, from here to the smallest branches.
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Smoke
When you smoke, the smoke comes down exactly this way.
As it cools, it leaves a sticky brown film behind. That is tar.
The tar catches in the hairs. Those dark clots are years of it.
Where enough gathers, the hairs stop moving, and this stretch stops cleaning itself.
Nothing is sweeping any more, so coughing is what is left to do it.
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Into the lungs
The windpipe ends just ahead.
It splits in two, and each way leads into a lung.
We are going through one of them now.
No more rings. The wall is softer here, and folded.
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Deeper in
Whatever is in the air travels down with it, the whole way.
And here it splits again, into something narrower still.
A real lung does this about twenty times over. We are going through two.
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The air sacs
The passage opens out here.
These round hollows are the air sacs, where every breath ends up.
You have hundreds of millions of them.
The wall between them and your blood is the thinnest thing in you.
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Air meets blood
Oxygen crosses here, into the blood on the other side.
Carbon dioxide comes back the other way, and you breathe it out.
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What else crosses
Carbon monoxide from the smoke crosses at the same wall.
It takes the seat oxygen was going to use, so less oxygen gets through.
Nicotine crosses here too, and reaches the rest of you within seconds.
