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How does blood clotting work?

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Quick answer

Blood clotting works by quickly sealing a wound to stop bleeding. Cell fragments called platelets rush to the injury and stick together, while a cascade of proteins weaves a mesh that traps blood cells into a solid plug. An injured blood vessel signals platelets to gather at the site.

Step by step

  1. An injured blood vessel signals platelets to gather at the site.
  2. Platelets stick together to form a temporary plug.
  3. A chain reaction of clotting proteins is activated.
  4. They build a fibrin mesh that traps cells into a firm clot.
  5. The clot dissolves once the vessel has healed.

People also ask

How does blood know where to clot?
A damaged vessel exposes signals that attract platelets and trigger clotting proteins right at the injury, so a clot forms only where needed.
What are platelets?
Tiny cell fragments in blood that rush to wounds, stick together, and kick off the clotting process to stop bleeding.
What happens if blood clots too much or too little?
Too little causes dangerous bleeding (as in hemophilia); too much can form clots that block vessels, causing strokes or heart attacks.

Part of the guide: How Your Body Works →