Science
How does blood clotting work?
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.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how blood clotting works.
Step by step
- 1An injured blood vessel signals platelets to gather at the site.
- 2Platelets stick together to form a temporary plug.
- 3A chain reaction of clotting proteins is activated.
- 4They build a fibrin mesh that traps cells into a firm clot.
- 5The clot dissolves once the vessel has healed.
Frequently asked questions
- 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.