What is Coagulation?
A '''coagulation''', also known as '''clot''', is a [[semi-solid]] substance [[blood]] forms on purpose to stop a leak. Blood does this especially when it is in [[air]]. When a person bleeds, the blood turns into a clot at the site of [[injury]] so no more blood can escape. A blood clot called a ''[[thrombus]]'' is one example of a blood clot. The clotting process is called ''coagulation.'' If a person gets a [[cut]] on their [[body]], they will bleed. To stop the bleeding, the [[human body]] first tells the [[liver]] to produce chemicals that will help the clot to form, the message coming from the [[brain]]. When the chemicals released by the liver arrive at the injury through the [[Circulatory system|circulation]], coagulation begins. At the same time, the brain also lessens the [[blood flow]] near the site of injury (by tightening the [[Vein|veins]] and [[Artery|arteries]] in that area), so that not as much blood is lost. There is a limit to how quickly a clot can form. If the cut is very deep and the person is bleeding too much, a clot may not be able to form and a lot of blood may be lost. Losing too much blood too quickly can be fatal. In medical emergencies where the blood circulation needs to be temporarily stopped (like to prevent death by [[hypovolaemia]]) they might use a [[Tourniquet]] on the limb if they can. == The details == [[File:Coagulation in vivo.png|right|thumb|400px|Blood coagulation pathways ''in vivo'' showing the central role played by thrombin]] Coagulation begins almost instantly after an injury to the blood vessel has damaged the [[endothelium]] lining the vessel. When blood is exposed to proteins such as [[tissue factor]] it starts changes to blood [[platelets]] and the plasma protein [[fibrinogen]], which is a clotting factor. [[Platelet]]s immediately form a plug at the site of injury. Proteins in the [[blood plasma]], called ''[[Coagulation factor|coagulation factors]]'' or ''[[Clotting factor|clotting]] factors'', respond in a complex [[cascade]] to form [[fibrin]] stran