Blood clots are formed by platelets and which plasma protein?

Blood clots are primarily composed of platelets (thrombocytes) and a plasma protein called fibrin. Fibrin is formed through a complex series of biochemical reactions known as the coagulation cascade. When blood vessels are damaged, platelets become activated and aggregate at the site of injury. They release various chemical signals that initiate the conversion of a plasma protein called fibrinogen into insoluble fibrin strands. These fibrin strands form a mesh-like network that traps platelets and other blood components, creating a stable blood clot to stop bleeding.