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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.
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 ...
This test is used to measure the contact activation pathway (intrinsic pathway) and the common pathway of clotting. [7] FXII is a zymogen, which means that it requires processing to attain its catalytic protease activity. Upon binding to surfaces, FXII alters in its conformation, giving it low-level protease activity.
Its role in the blood clotting is the initiation of thrombin formation from the zymogen prothrombin. Thromboplastin defines the cascade that leads to the activation of factor X—the tissue factor pathway. In doing so, it has replaced the previously named extrinsic pathway in order to eliminate ambiguity.
In coagulation, the coagulation factor X can be activated into factor Xa in two ways: either extrinsically or intrinsically. The activating complexes are together called tenase . Tenase is a blend word of "ten" and the suffix "-ase", which means, that the complex activates its substrate (inactive factor X) by cleaving it.
The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time (aPTT or APTT), is a blood test that characterizes coagulation of the blood.A historical name for this measure is the Kaolin-cephalin clotting time (KCCT), [1] reflecting kaolin and cephalin as materials historically used in the test.
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
This measures the quality of the extrinsic pathway (as well as the common pathway) of coagulation. The speed of the extrinsic pathway is greatly affected by levels of functional factor VII in the body. Factor VII has a short half-life and the carboxylation of its glutamate residues requires vitamin K.