Thrombin is an enzyme in the blood that plays a crucial role in the process of blood coagulation. It is produced from a protein called prothrombin and helps convert fibrinogen, another protein, into fibrin, which forms a mesh that stabilizes blood clots. This process is essential for stopping bleeding when injuries occur. In addition to its role in clot formation, thrombin also has other functions, such as activating platelets, which are small cell fragments that help in the clotting process. Proper regulation of thrombin is vital, as too much can lead to excessive clotting, while too little can result in uncontrolled bleeding.