Revised model of coagulation Revised model of coagulation. Schematic overview of the coagulation reactions in which several revisions have been made as compared to the classic cascade model of coagulation. The tissue factor–factor VIIa complex of the extrinsic pathway also activates factor IX, and thrombin activates factor XI, in a positive feedback loop. The factor IX–dependent amplification of factor Xa generation is necessary for hemostatic fibrin formation at low tissue factor concentrations, because tissue factor–factor VIIa–mediated factor X activation is inhibited by tissue factor pathway inhibitor (TFPI). Procoagulant extrinsic pathway components are indicated in black, the part of the intrinsic coagulation pathway that is not necessary for hemostasis is indicated in gray. Anticoagulant mediators are indicated in red. AP, antiplasmin; APC, activated protein C; AT, antithrombin; Hep, heparin; HK, high-molecular-weight kininogen; PAI, plasminogen activator inhibitor; PZ, protein Z; TAFI, thrombin-activatable fibrinolysis inhibitor; TF, tissue factor; Tm, thrombomodulin; tPA, tissue plasminogen activator; uPA, urokinase plasminogen activator; ZPI, protein Z–dependent protease inhibitor. Source: Molecular Biology and Biochemistry of the Coagulation Factors and Pathways of Hemostasis, Williams Hematology, 9e Citation: Kaushansky K, Lichtman MA, Prchal JT, Levi MM, Press OW, Burns LJ, Caligiuri M. Williams Hematology, 9e; 2015 Available at: http://hemonc.mhmedical.com/DownloadImage.aspx?image=/data/books/1581/kau_ch113_f028.png&sec=108080009&BookID=1581&ChapterSecID=108079516&imagename= Accessed: September 29, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved