In biology,<unk>  or<unk>  is a process to prevent and stop bleeding, meaning to keep blood within a damaged blood vessel (the opposite of<unk>  is hemorrhage). It is the first stage of wound healing. This involves coagulation, which changes blood from a liquid to a gel. Intact blood vessels are central to moderating blood's tendency to form clots. The endothelial cells of intact vessels prevent blood clotting with a heparin-like molecule and thrombomodulin, and prevent platelet aggregation with nitric oxide and prostacyclin. When endothelium of a blood vessel is damaged, the endothelial cells stop secretion of coagulation and aggregation inhibitors and instead secrete von Willebrand factor, which initiate the maintenance of<unk>  after injury.<unk>  involves three major steps: * vasoconstriction * temporary blockage of a hole in a damaged blood vessel by a platelet plug * blood coagulation (formation of fibrin clots) These processes seal the injury or hole until tissues are healed.
Hemostasis
Coagulation
Lymphangiogenesis
Vasoactivity
Neurosecretion
Digestion
Intravasation
Thermoregulation