Virchow in 1856 described the famous triad:

1. Stasis

2. Endothelial damage

3. Hypercoaguable states

The basis of the coagulation system is based on the coagulation cascade. The end points of this cascade include the formation of thrombin and fibrin. Throughout this system there can be defects in the multiple enzymes or extrinsic factors contributing to its dysfunction.

There are several interrelated stages in the formation of a clot:

• Vasoconstriction

• Platelet aggregation

• Intrinsic pathway

• Extrinsic Pathway

The initial response in injury is a transient vasoconstriction which is linked to platelet plug and fibrin formation. Vasoconstriction is mediated through intrinsic mechanisms and various vasoactive agents (thromboxane A2 and serotonin) released during platelet aggregation.

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