Blood circulation
If you are going to inject drugs it is important to understand how blood flows around your body.

There are three types of blood vessel:

• Arteries which carry oxygenated blood, at high pressure, from the heart and lungs to the tissues of the body
   
• Veins which carry blood back to the heart and lungs at low pressure

and, joining them together, millions of tiny blood vessels called

• Capillaries which transfer oxygen and waste products between cells and blood in the body tissues and lungs.

You must only inject into veins. The next few pages look in detail at veins and arteries...

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