Several factors are involved
- Endothelial factor
- Smoothness of endothelium prevents platelet adhesion
- Glycocalyx present over endothelium repel clotting factors (proteins: anions)
- Velocity of blood prevents stasis of blood and coagulation
- Presence of natural anticoagulants like Heparin, Protein C
- Simultaneous activation of fibrinolytic system along with clotting mechanism
- Liver removes activated clotting factors from circulation