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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]
Factor X is activated, by hydrolysis, into factor Xa by both factor IX with its cofactor, factor VIII in a complex known as intrinsic pathway; and factor VII with its cofactor, tissue factor in a complex known as extrinsic pathway. [6] It is therefore the first member of the final common pathway or thrombin 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 ...
Tissue factor, also called platelet tissue factor or Coagulation factor III, [5] is a protein present in subendothelial tissue and leukocytes which plays a major role in coagulation and, in humans, is encoded by F3 gene. Its role in the blood clotting is the initiation of thrombin formation from the zymogen prothrombin.
The activation of thrombin is a critical reaction in the coagulation cascade, which functions to regulate hemostasis in the body. To produce thrombin, the prothrombinase complex cleaves two peptide bonds in prothrombin, one after Arg 271 and the other after Arg 320 . [ 1 ]
The coagulation cascade. Factor XII (FXII, Hageman factor) is a plasma glycoprotein of approximately 90 kDa and is part of the coagulation cascade. It activates factor XI and prekallikrein in vitro. FXII is activated to FXIIa by negatively charged surfaces such as glass, initiating the intrinsic pathway. [12]
Factor XI (FXI) is produced by the liver and circulates as a homo-dimer in its inactive form. [9] The plasma half-life of FXI is approximately 52 hours. The zymogen factor is activated into factor XIa by factor XIIa (FXIIa), thrombin, and FXIa itself; due to its activation by FXIIa, FXI is a member of the "contact pathway" (which includes HMWK, prekallikrein, factor XII, factor XI, and factor IX).
The kinin-kallikrein system plays a small role in coagulation. Blood clotting cascade. The blood clotting cascade consists of the intrinsic and extrinsic pathway, both of which create thrombin, a protease involved in blood clotting. The intrinsic pathway requires kininogen, specifically high molecular weight kininogen, as a cofactor.