Coagulation is a process in which blood forms clots. The coagulation system is a complex network of proteins and cells that work together to form a clot. It is composed of two pathways: the intrinsic pathway and the extrinsic pathway. The intrinsic pathway is activated by contact with damaged tissue, while the extrinsic pathway is activated by contact with tissue factor. The coagulation system is important for preventing excessive bleeding and maintaining normal blood flow.