Which substance, formed in the liver, acts as an anticoagulant to prevent blood clotting?

Heparin is a substance produced by the liver that acts as an effective anticoagulant, meaning it helps to prevent blood clotting. It does this by inhibiting certain factors in the blood coagulation process, particularly by enhancing the activity of antithrombin III, which inactivates thrombin and other clotting factors. This property is crucial in various medical settings, such as during surgeries or in patients at risk for clot formation, as it assists in preventing the formation of harmful clots that can lead to conditions like thrombosis.

Fibrinogen, prothrombin, and platelets play different roles in the clotting process. Fibrinogen is a protein that is converted into fibrin, which forms the mesh-like structure of a blood clot. Prothrombin is a precursor to thrombin, an enzyme essential for the clotting cascade. Platelets are small cell fragments involved in the initial response to vascular injury and are critical in forming the primary platelet plug that begins the clotting process. However, none of these three components function as anticoagulants in the same manner that heparin does.