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Blood and the Body

The Clotting Process: What You Need to Know

The body has an automatic response to injury called "blood clotting." This well-organized system has several parts that work seamlessly together. The system ensures that blood, which needs to be in liquid form inside the body, can clot in an instant with injury, preventing blood loss.

First, injured blood vessels constrict, reducing the amount of blood that can escape. Next, platelets (small blood cell fragments) rush to the scene as "first responders," triggering the clotting events that follow. The platelets stick together at the site of the injury forming a “platelet plug.”

This plug, however, is not enough by itself to stop blood loss. A reinforcement, called fibrin, is made by a domino-like process of clotting proteins, the "clotting cascade," each one activating the next to strengthen the clot and hold it in place.

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Last Reviewed: May 01, 2012

Susan   Wentz, MD, MS Susan Wentz, MD, MS
Director, Area Health Education Center
School of Medicine
Case Western Reserve University