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Have you ever thought about how our body prevents us from bleeding to death when we get injured? The coagulation cascade is the mechanism in charge of this and just as any other, it is very well regulated in order to respond as soon as a leak is detected.

The coagulation cascade and its main actors 

Bruises and scabs are neither pleasant nor pretty but they are part of a vital mechanism that our body requires to avoid excessive lose of blood after an injury. This mechanism is known as hemostasis or coagulation and its main purpose is to form a blood clot as fast as possible after a tissue, an organ or a blood vessel is damaged. During the process, cells, proteins and other substances participate in the formation of the clot and if any of these components gets disrupted in any way, it can cause severe alterations in the formation of the clot, putting our life at risk.

Platelets, tiny sticky bricks 

Platelets, also known as thrombocytes, are the cells that participate in the coagulation process. These cells do not have a nucleus and are basically just pieces of bigger cells, known as megakaryocytes, that live in the bone marrow. 

Platelets are therefore produced in the bone marrow and when mature, they travel in the circulatory system.

These cells have to fulfill three major functions during coagulation. The first one has to do with their adherence to the blood vessel that has been damaged and has a leak. Their second function is to form a big plug in order to cover the whole damaged area; for this, they attach to other platelets. Their third and final function is to promote the coagulation process by producing small molecules on their surface to activate other molecules that are also part of this mechanism.

These cells do not only participate in the coagulation process, but are also part of the immune system. They interact with other immune cells, such as white blood cells, and they release several substances that promote inflammation.

Coagulation factors: keeping everything together

Apart from the platelets, there are other proteins that participate in the coagulation process.

These proteins are known as coagulation factors and what they basically do is to orchestrate the whole coagulation process.

The platelets are the building blocks that construct the blood clot, but the factors are the builders that control this amazingly organized process.  All of the factors are essential for the whole hemostasis process to take place, but fibrinogen and thrombin are some of the most known ones.

Thrombin is the protein that activates platelets. It binds to the surface of these cells, switching them on and promoting their aggregation to form the clot.

Thrombin also converts fibrinogen into fibrin, which acts like the concrete that keeps platelets together and stabilizes the clot. Without fibrin, platelets would certainly aggregate at the site of injury but they would not be able to stay together by themselves, due to the blood flow pressure.

This process has to be very well balanced in order to avoid the formation of clots when they are not needed and to ensure that if there is a bleeding, the cascade will function properly to avoid massive blood loss. This is why some of the factors promote the formation of the clot, while others inhibit it.

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