Coloured scanning electron micrograph (SEM) showing an activated platelet (thrombocyte) trapped in a mesh of fibrin strands (beige) and erythrocytes (red) during the hemostatic process of wound healing. The shell (green) of the platelet has collapsed and numerous vesicles (blue) have been released into the wound area. The vesicles contain a large number of enzymes and growth factors, thereby attracting cells needed during the following stages of wound healing. Vessel wall injury triggers the attachment and activation of platelets and the generation of fibrin polymers from fibrinogen. Platelets and fibrin combine to form a blood clot containing erythrocytes (red blood cells). Magnification: ?5000 when printed at 10 centimetres wide.