You fall off your bike and scrape your knee. Blood drips out, but soon a scab starts to form and the bleeding stops. Sounds simple, doesn’t it? However, if you could zoom in to see what’s happening on a molecular scale, it’s not simple at all. Your blood includes thirteen different protein molecules called clotting factors. When you injure yourself, these clotting factor proteins all connect and work together to form a solid clot (also known as a scab). If you were missing even ONE of those thirteen proteins, the clot wouldn’t form, and the dangerous bleeding would continue. This is exactly what happens in a disease called hemophilia (HEE-mo-FEEL-ya). People with hemophilia are missing one of the proteins needed for blood clotting.
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