Which pathway is associated with heparin in coagulation?

Heparin is known to primarily affect the intrinsic pathway of coagulation. It achieves this by enhancing the action of antithrombin III, which inactivates several clotting factors, particularly factor Xa and thrombin (factor IIa). The intrinsic pathway, part of the coagulation cascade, involves factors such as XII, XI, IX, and VIII, and is primarily activated by contact with negatively charged surfaces or damaged endothelial cells.

When heparin is administered, it rapidly inhibits the thrombin and factor Xa in this pathway, preventing the formation of fibrin and thus impeding clot formation. This action makes heparin a crucial anticoagulant in various medical conditions, including acute coronary syndrome, deep vein thrombosis, and during certain surgical procedures.

The extrinsic pathway, which is activated by tissue factor and leads to the rapid initiation of clotting, is not significantly affected by heparin. The common pathway represents the convergence point of both the intrinsic and extrinsic pathways and thus is indirectly influenced by heparin but is not the primary focus. The term "clotting pathway" is less specific and does not directly relate to the distinct pathways recognized in the coagulation cascade.