Thrombomodulin is a protein found on the surface of endothelial cells, which line blood vessels. It plays a crucial role in regulating blood coagulation by binding to thrombin, an enzyme involved in blood clotting. When thrombomodulin binds to thrombin, it changes thrombin's activity, promoting the activation of protein C, which helps to prevent excessive clotting. By activating protein C, thrombomodulin helps to break down fibrin, a key component of blood clots, and inhibits the formation of new clots. This process is essential for maintaining a balance between clot formation and dissolution, ensuring proper blood flow and preventing conditions like thrombosis.