The role of thrombin in the coagulation cascade

Trombin je enzimski aktivan protein koji ima centralnu ulogu u procesu koagulacijske kaskade. Nastaje aktivacijom protrombina, plazmatskog proteina koji se sintetizira isključivo u jetri. U početku procesa koagulacijske kaskade, male količine trombina aktiviraju faktore V, VIII i XI koji pozitivnom povratnom spregom pospješuju dodatno generiranje trombina. Nagli skok aktiviranog trombina u kasnijoj fazi, pretvaranjem fibrinogena u fibrin posreduje stvaranje fibrinske mrežice i krvnog ugruška. Također, aktiviranjem faktora XIII pojačava čvrstoću fibrinske mrežice te sprječava njenu fibrinolitičku razgradnju plazminom. Vezanjem za trombomodulin, aktivira TAFI te dodatno stabilizira ugrušak. Također, trombin vezanjem za trombomodulin pokreće i sustav prirodnih antikoagulanasa aktivirajući protein C, te time sprječava nekontrolirano generiranje trombina. Stoga se i učinak kako antikoagulantnih tako i prokoagulantnih lijekova postiže pojačavanjem ili inhibicijom djelovanja trombina.Thrombin is an enzyme that has a central role in a process of coagulation cascade. It is produced by the activation of prothrombin, a plasma protein that is synthesized exclusively in the liver. Small amounts of thrombin that are present at the beginning of the coagulation cascade, activate factors V, VIII and XI which promotes further thrombin generation through positive feedback. An abrupt jump in activated thrombin at a later stage, mediates the formation of the fibrin network and blood cloth, by converting fibrinogen to fibrin. Through activation of factor XIII, thrombin enhances the strength of the fibrin network and prevents its fibrinolytic degradation by plasmin. In a complex with thrombomodulin it activates TAFI and further stabilizes the clot. Furthermore, thrombin activates protein C thus activating the system of natural anticoagulant, and therefore preventing the uncontrolled generation of thrombin. Finally, the activity of both anticoagulant and procoagulant drug is achieved by the inhibition or the enhancement of thrombin activity