Thrombosis and Embolism Flashcards
Thrombosis
The process leading to thrombus formation
Thrombus’ main constituents
Platelets and fibrin
When can thrombosis be physiological
To prevent bleeding when a vessel wall is breached
What process limits physiological thrombosis and how relate to pathological thrombosis
Fibrinolysis
Thrombosis becomes pathological when it is not controlled by fibrinolysis
What holds a thrombus together
Fibrin
Describe the process of physiological thrombosis
Vessel wall is breached and so circulating platelets aggregate to plug the gap
Platelets release factors which trigger coagulation cascade which converts fibrinogen into insoluble fibrin that wraps together platelets and entrapped RBCs and WBCs
Plasmin
Active enzyme that fragments/degrades fibrin and thus blood clots
Fibrin degradation products (FDPs)
Fragmented bits of fibrin after degradation
Describe the process of normal finrinolysis
Inactive plasminogen in plasma becomes plasmin via plasminogen activators (specifically tissue plasminogen activator t-PA)
When fibrin is formed, plasminogen and t-PA bind to it; t-PA activates nearby plasminogen, leading to fibrin degradation
This controls thrombus size
How might pathological thrombosis occur (simple)
Thrombus grows beyond vessel healing requirements and continues to grow to a size and rate beyond which the fibrolytic system is incapable of controlling the size
D-Dimers and D-Dimer test
D-Dimers are a breakdown product of fibrin mesh, stabilised by factor XIII;
Increased levels may indicate thrombotic events
Factors that predispose thrombus formation (Virchow’s Triad)
Damage to vessel wall (especially endothelium)
Stasis of blood
Change in blood character (especially increases in platelets, RBCs and viscosity)
How is arterial thrombosis most likely to occur
Main predisposing factor is vessel wall damage
How is venous thrombosis most likely to occur
Stasis is the most important factor
How is thrombosis of the heart most likely to occur in the ventricles
Chamber wall damage is the most important factor here