How do extrinsic and intrinsic coagulation systems operate in the pathogenesis of deep venous thrombosis (DVT)?

Updated: Jun 05, 2019
  • Author: Kaushal (Kevin) Patel, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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The extrinsic system operates as the result of activation by tissue lipoprotein, usually released as the result of some mechanical injury or trauma. The intrinsic system usually involves circulating plasma factors. Both of these pathways come together at the level of factor X, which is activated to form factor Xa. This in turn promotes the conversion of prothrombin to thrombin (factor II). This is the key step in clot formation, for active thrombin is necessary for the transformation of fibrinogen to a fibrin clot.

Once a fibrin clot is formed and has performed its function of hemostasis, mechanisms exist in the body to restore the normal blood flow by lysing the fibrin deposit. Circulating fibrinolysins perform this function. Plasmin digests fibrin and also inactivates clotting factors V and VIII and fibrinogen.

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