Figure 1. Triggers of arterial and venous thrombosis.

a, Artery. The primary trigger of arterial thrombosis is rupture of an atherosclerotic plaque. This involves disruption of the endothelium and release of constituents of the plaque into the lumen of the blood vessel. b, Vein. By contrast, in venous thrombosis, the endothelium remains intact but can be converted from a surface with anticoagulant properties to one with procoagulant properties. Venous thrombosis can be triggered by several factors: abnormal blood flow (such as the absence of blood flow); altered properties of the blood itself (thrombophilia); and alterations in the endothelium.