Q.Which of the following is not involved in blood clotting?

Blood coagulation (clotting) is the mechanism that stops excessive blood loss after an injury by forming a solid plug at the site of damage. It begins the instant a vessel's inner endothelial lining is torn and the underlying connective tissue is exposed to blood: platelets stick to the exposed collagen fibres and release chemicals that recruit more platelets, quickly forming a temporary platelet plug. Substances from these clumped platelets and from the damaged tissue combine with clotting factors already in the plasma to generate a prothrombin-activator substance, which converts the inactive plasma protein prothrombin into its active enzyme form, thrombin - a step that requires both calcium ions and vitamin K. Thrombin then converts a second plasma protein, fibrinogen, into long insoluble threads of fibrin, which weave into a mesh that traps blood cells and platelets and physically seals the wound. As the mesh matures, the …