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The coagulation system

The coagulation system or haemostasis describes the reactions that are responsible for a bleeding to stop. Being a haemophiliac, implies that you have an increased bleeding risk due to an hereditary lack or deficiency of one or more proteins that circulate in the blood. In case of a bleeding, these proteins are necessary in order to ensure a well-functioning coagulation.

The following section briefly describes the blood clotting mechanism and how this is defective in people with haemophilia.

 

Normal blood coagulation

Blood coagulation, or haemostasis, characterises the body’s ability to manage and prevent blood loss in case of injuries. The haemostasis mechanism is usually divided into primary and secondary haemostasis.

Primary haemostasis begins by contraction of the vessel wall in order to minimise the blood flow to the injured site.

In the next step, blood platelets adhere to the injured vessel wall and form a plug that temporarily stops the bleeding. In this phase, a protein, the so-called von Willebrand factor, functions as a binding glue, allowing the platelets to stick to the vessel wall and to each other.

Thereafter, the secondary haemostasis mechanism is activated during which, among other things, proteins circulating in the blood react with one another in a complex chain reaction. These proteins are referred to as coagulation factors and are described by Roman numerals from I to XII. Secondary haemostasis results in a fibrinogen network, which covers the surface of the plug and thereby stops the blood clot from loosening.

Some people have an hereditary deficiency or defect of one or several coagulation factors, which implies that the blood cannot coagulate as it should once a bleeding occurs. Haemophilia A and B, and von Willebrand disease are now the most common reasons for an increased bleeding tendency. Haemophilia A leads to deficiency of coagulation factor VIII, and Haemophilia B involves a deficiency of factor IX. Such deficiencies prevent the cascade of reactions that normally occurs in secondary haemostasis. 

 

 

Page updated: 2016-06-17