within the blood plasma, heparin by itself does not have any anticoagulant activity. Unfractionated Heparin binds to the inactive antithrombin. This binding activates it through a confirmation change, then allows the active antithrombin to bind and interact with Factor Xa, leading to its effect in the plasma to stop the conversion of thrombin from prothrombin, thereby inhibiting the production of fibrin from fibrinogen. The end result is preventing the formation of any further clots. Now, in the same way, the unfractionated heparin binds and consequently causes a confirmation change to the inactive antithrombin. This accelerates the interaction between the active antithrombin and thrombin. Unfractionated Heparin serves as a catalytic template to block between thrombin and fibrin, which is responsible for its inhibition of fibrin to fibrin. Therefore, the end result is to prevent further formation of any clots within the plasma. Now, low molecular heparin binds to

the inactive antithrombin this binding causes a confirmation change and activates antithrombin. This in turns accelerates the interaction between the active antithrombin and Factor ta, leading to the similar effect, which is the decrease of prothrombin to thrombin, which further inhibits fibrinogen to fibron, and thus prevents further blood clotting. However, with low molecular heparin, it does bind to the inactive antithrombin, activating it. This accelerates the interaction between the active antithrombin and thrombin, which is responsible for the inhibition of fibron production from fibrinogen. However, with low molecular heparin, it is too short to bridge the antithrombin to thrombin, which explains its reduced activity on thrombin.

Heparin - Mechanism of Action

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