<prompt> Heparin acts by activation ofPlasminTPAAntithrombin IIIFibrinolysin  <response>: Ans: c Antithrombin III Ref: Ganong 22nd edp.543. Heparin acid proteoglycan binds to cationic site of antithrombin III and greatly potentiates its activity. Heparin antithrombin complex removes free thrombin from blood. Thrombin is an activator of factor 5 and 8. Heparin- antithrombin complex also inhibits activated clotting factors IX. X, XI, XII. Antidote for heparin is Protamine sulphate. Direct thrombin inhibitors are bivaluridin, lepirudin and agratroban. Plasminogen is activated by tissue plasminogen activator t-PA. Plasminogen profibrinolysin, when activated becomes plasmin fibrinolysin, which digests fibrin and fibrinogen with the production of fibrinogen degradation products FDP that inhibit thrombin. It also lyses prothrombin, factor V, VIII and XII. 