Files in this Data Supplement:

• Movie - (Macromedia Flash Player) (822 kb). This figure illustrates the process by which a blood clot is formed. At the beginning of the animation, a plaque in the inner wall (the endothelium) of an artery has been ruptured; this injury attracts platelets which, together with red blood cells, white blood cells, and plasma, make up blood. Some platelets begin to adhere to the plaque. This is adhesion. Then more and more platelets aggregate or stick to one another. This is aggregation. The platelets begin to form strands that mesh together becoming a net-like substance (fibrin), and red blood cells become trapped in the fibrin net, creating a clot and reducing the amount of blood that can flow past the plaque in the artery. This is coagulation.