Virchow’s triad for thrombosis include all except -
1.Stasis
2.Endothelial injury
3.Hypercoagulability
4.Platelet thrombus
Explanation
Thrombosis
Thrombosis is the formation of a blood clot (thrombus) inside a blood vessel or heart, obstructing the flow of blood through the circulatory system.
Then what is the difference between formation of normal hemostatic plug and thrombosis ?
When a blood vessel is injured, the body uses platelet and fibrin to form a blood clot as the first step to prevent blood loss → hemostasis.
If that mechanism causes too much doting, a thrombus is formed i.e., exaggeration of hemostatic process leads to thrombus formation.
In other terms, hemostasis is a self limited process i.e., there is spontaneous resolution of hemostatic plug with subsequent repair of the injury, while thrombosis is not self limited and the thrombotic clot does not undergo resolution spontaneously rather it causes obstruction to blood flow.
Thrombosis may occur without injury (e.g., in hypercoagulable state), while hemostatic plug is formed only after injury.
Pathogenesis of thrombosis
Thrombosis is caused by abnormalities in one or more of the following three (Virchow’s triad) : -
Vascular (endothelial) injury.
Abnormal blood flow (stasis or turbulence).
Blood hypercoagulability.
How do these mechanisms lead to thrombosis?
Endothelial injury with formation of clot has already been explained earlier.
Blood hypercoagulability, as the name suggests, there is increase tendency of clot formation due to alteration in coagulation pathway that predisposes to thrombus. It may occur in many primary (genetic) or secondary (acquired) conditions.
Disturbances in blood flow
Stasis Stasis is the major factor in the development of venous thrombus.
Turbulence contributes to arterial and cardiac thrombosis.
Normal blood flow is laminar such that the platelets flow centrally in the vessel lumen, separated from the endothelium by a slower-moving clear zone of plasma.
Stasis and turbulence leads to thrombosis by -
Disruption of laminar flow brings platelets into contact with endothelium.
Prevent dilution of activated clotting factors by fresh flowing blood.
Retard the inflow of clotting factor inhibitors.
Turbulence can cause endothelial injury or dysfunction.