Mechanism of Thrombolysis

Under normal circumstances there is no plasminogen activation occurring in plasma, the action of the fibrinolytic system is confined to fibrin. When fibrin is formed, a small amount of plasminogen activator and plasminogen adsorb to it and plasmin is created in situ to catalyze the degradation of fibrin (Figure 3).20 Naturally occurring plasminogen

Figure 3 Schematic diagram showing the process of fibrinolysis and its control. D-dimers, breakdown product of fibrin.

activators are either tissue-type plasminogen activator (t-PA) or single chain urokinase-type plasminogen activator (scu-PA), both of which are synthesized by the endothelial wall.

The fibrinolytic system is tightly controlled and is normally restricted in the thrombus (Figure 3). Endothelial cells secrete plasminogen activator inhibitor-1 (PAI-1), which inactivates t-PA in the plasma but not that in the thrombus; in addition, the plasma t-PA has a short half-life (5-8 min). Also, a2-antiplasmin, a physiological bound serine protease inhibitor, forms an inert complex with the circulating plasmin but does not act on fibrin-bound plasmin in the thrombus.4 Any disturbance in this system can cause either excessive thrombus formation, if there is insufficient activation of the thrombolytic system or if there are excessive inhibitors,21 or bleeding tendency, if there is overstimulation of the thrombolytic system and deficiency in the release of inhibitors.20

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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