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The division of coagulation in two pathways is arbitrary, originating from laboratory tests in which clotting times were measured either after the clotting was initiated by glass, the intrinsic pathway; or clotting was initiated by thromboplastin (a mix of tissue factor and phospholipids), the extrinsic pathway. [31]
[3] [4] Factor X can be activated by both the factor VIIa-tissue factor complex of the extrinsic coagulation pathway and by the tenase complex of the intrinsic pathway. The intrinsic tenase complex is composed of both factor IXa and factor VIIIa.
Therefore, although the coagulation cascade can be triggered in vitro through the intrinsic pathway only, in vivo coagulation is triggered by the extrinsic pathway. However, the model better describing how coagulation works is the so-called cell-based model, a more integrated picture of the whole process, in which phospholipid surfaces, such as ...
Together with factor VIIa, tissue factor forms the extrinsic pathway of coagulation. This is opposed to the intrinsic (amplification) pathway, which involves both activated factor IX and factor VIII. Both pathways lead to the activation of factor X (the common pathway), which combines with activated factor V in the presence of calcium and ...
The two arms of the contact system. PKa's cleavage of HK liberates BK and promotes inflammation. FXIIa's cleavage of FXI initiates coagulation. In the contact activation system or CAS, three proteins in the blood, factor XII (FXII), prekallikrein (PK) and high molecular weight kininogen (HK), bind to a surface and cause blood coagulation and ...
Blood coagulation pathways in vivo showing the central role played by thrombin. Factor Xa is the activated form of the coagulation factor X, also known as thrombokinase. Factor X is an enzyme, a serine endopeptidase, which plays a key role at several stages of the coagulation system. Factor X is synthesized in the liver.
Characteristics of the velocity of passage of the intrinsic coagulation pathway; Poor plasma (the most convenient to work with, but no realization of the thrombocyte clotting mechanism) Contact activation pathway; Prothrombin time test (or prothrombin test, INR, PT) – velocity of passage of the extrinsic blood coagulation pathway Poor plasma
The ELT measures fibrinolysis by clotting the euglobulin fraction (primarily the fibrinolytic factors fibrinogen, PAI-1, tPA, α 2-antiplasmin, and plasminogen) from plasma and then observing the time required for clot dissolution. A shortened lysis time indicates a hyperfibrinolytic state and bleeding risk.