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Inside
You are inside one of your own veins.
Everything here is happening in you, right now.
Click to move on, and take it at your own pace.
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Red cells
The red discs streaming past you are red blood cells.
They carry oxygen. These ones have already given theirs away.
That is why they look so dark. They are going back to your lungs for more.
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White cells
The larger pale ones, rolling along the wall, are white blood cells.
They are your defence, looking for anything that should not be here.
They travel slowly and close to the wall, so they can stop where they are needed.
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Platelets
The small pale specks are platelets.
When you cut yourself, they rush over and stick to each other.
That plug is what stops the bleeding, and the start of every scab you have had.
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Plasma
All of it is carried in a pale fluid called plasma.
Plasma is mostly water, with salt in it.
And sugar, from the last thing you ate. That is the fuel every part of you runs on.
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The wall
The soft blue surface around you is the wall of the vein.
It is thin, and it gives a little with every heartbeat.
All of this is on its way back up to your heart.
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One-way doors
Look ahead. The passage closes to a narrow slit.
This is a valve, and it opens only one way.
Blood in your legs has to climb all the way back up to your heart.
Nothing pumps it up. Your muscles squeeze, and valves like this stop it falling back.
So when you sit still for hours, very little moves it along.
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Over the years
The wall along here looks different. Duller, and rougher.
Too much sugar in your blood, for years, slowly wears it.
A rough wall is a wall that things catch on.
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A blockage
And here, behind the next valve, something has.
Blood that stopped moving gave the platelets time to gather.
They caught on each other, and held. That is a clot.
Look how little room is left to get past it.
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A piece breaks away
Sometimes a piece comes away.
There it goes, past you, carried the way you came.
It travels up through your heart, and into a lung.
There the passage is too narrow to let it through, and it stops.
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What helps
This is why you are told to get up and walk about on a long flight.
Moving your legs is what moves this along.
Here is another valve, in a clear vein, doing its job.
Now you know what that advice was always for.
