Primary hemostasis and platelet function | Start and duration of thrombosis prophylaxis

Primary hemostasis and platelet function

The aim of primary hemostasis is to stop bleeding by forming a platelet (thrombus). The platelets are naturally involved in this process, as are a number of different factors (e.g. von Willebrand factor) and receptors. If, for example, a blood vessel is injured, it contracts in the primary reaction (vasoconstriction) to minimize blood loss and slow down the blood flow.

The components of the now exposed tissue as well as the inner layer of the vessels (endothelium) now ensure that the platelets from the blood stream can adhere exactly there. The platelets are further activated by the adhesion, emptying their contents and changing their shape. With the formation of a clot (also known as a white blood clot), primary hemostasis is complete. It serves as a “temporary seal”.

Secondary Hemostasis

For permanent closure, the plug must be replaced by a fibrin thrombus. For this purpose, the fibrinogen (or factor I of the blood clotting cascade), which occurs in an inactive precursor in the blood, must be converted to fibrin.This requires the activation of various coagulation factors in the blood in a relay-like manner. This preceding blood coagulation cascade consists of an exogenous (or extrinsic) and an endogenous (or intrinsic) pathway, which represent different activation pathways and lead to a common final pathway.

The endogenous pathway includes the factors XII, XI, IX, VIII as well as calcium as the most important components. Factors III and VII as well as calcium are the most important components of the exogenous pathway. The common endogenous pathway begins with the activation of factor X and the other factors V, II, XIII and I. The fibrin now activated at the end of the cascade cross-links and sticks together and is finally called the red thrombus, since the other components of the blood composition (e.g. the red blood cells) are also caught in the fibrin network.

Laboratory chemical testing

The endogenous pathway can be measured in the laboratory by the so-called partial thromboplastin time PTT. The exogenous pathway is checked by the quick value or INR. Both test methods also measure the common endogenous pathway.