Coagulation is a complex process by which the blood forms clots to block and then heal a lesion/wound/cut and stop the bleeding. It is a crucial part of hemostasis - stopping blood loss from damaged blood vessels. In hemostasis a damaged blood vessel wall is plugged by a platelet and a fibrin-containing clot to stop the bleeding, so that the damage can be repaired.
Coagulation involves a cellular (platelet) and protein (coagulation factor) component.
When the lining of a blood vessel (endothelium) is damaged, platelets immediately form a plug at the site of the injury, while at the same time proteins in the blood plasma respond in a complex chemical reaction, rather like a waterfall, to form fibrin strands which reinforce the platelet plug.
Primary hemostasis - when the platelets gather at the site of an injury to plug (block) it.
Secondary hemostasis - proteins (coagulation factors) act in a series of chemical reactions to strengthen the plug and allow healing to begin.
