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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]
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 ...
Thromboplastin, by itself, could activate the extrinsic coagulation pathway. When manipulated in the laboratory, a derivative could be created called partial thromboplastin, which was used to measure the intrinsic pathway. This test is called the aPTT, or activated partial thromboplastin time. It was not until much later that the subcomponents ...
FDPs compete with thrombin, and thus slow down clot formation by preventing the conversion of fibrinogen to fibrin. This effect can be seen in the thrombin clotting time (TCT) test, which is prolonged in a person that has active fibrinolysis. Antibody-antigen technology can measure FDPs and a specific FDP, the D-dimer. This is more specific ...
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.
[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. [5] [6] The activation peptide is released when factor X is activated to factor Xa, but the heavy ...
High-molecular-weight kininogen (HMWK or HK) is a circulating plasma protein which participates in the initiation of blood coagulation, and in the generation of the vasodilator bradykinin via the kallikrein-kinin system. HMWK is inactive until it either adheres to binding proteins beneath an endothelium disrupted by injury, thereby initiating ...
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 ...