Put your fingers on your wrist. Feel something throbbing just below the surface of your skin? It's your pulse, letting you know that your heart is working hard. Each time your heart beats, it pumps blood along a network of tubes called blood vessels. |
![](https://webarchive.library.unt.edu/eot2008/20080917180630im_/http://www.nlm.nih.gov/changingthefaceofmedicine/img/spacer.gif) |
This network, along with your heart, is known as the circulatory system, and it reaches every cell in your body.
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