Atherosclerosis occurs when the endothelium of a blood vessel becomes damaged. This may due to various reasons such as high blood pressure or toxins from cigarette smoke. This causes an inflammatory response whereby white blood cells, cholesterol, calcium salts and fibrous tissue accumulate in the area. A plaque or atheroma forms.This causes hardening of the artery as it loses its elasticity. The lumen of the artery becomes narrower. This increases the risk of thrombosis.