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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 ...
The prothrombin time (PT) – along with its derived measures of prothrombin ratio (PR) and international normalized ratio (INR) – is an assay for evaluating the extrinsic pathway and common pathway of coagulation. This blood test is also called protime INR and PT/INR.
Traditional models of coagulation developed in the 1960s envisaged two separate cascades, the extrinsic (tissue factor (TF)) pathway and the intrinsic pathway. These pathways converge to a common point, the formation of the Factor Xa/Va complex which together with calcium and bound on a phospholipids surface, generate thrombin (Factor IIa) from ...
[4] [5] [6] The ability of FXII to bind to negatively charged surfaces and activate coagulation forms the basis of the aPTT test, in which artificial materials act as a surface for contact activation. This test is used to measure the contact activation pathway (intrinsic pathway) and the common pathway of clotting. [7]
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 ...
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