Atherosclerosis is a type of arteriosclerosis caused by a build-up of plaque in the inner lining of an artery. (Arteriosclerosis is a general term for thickening or hardening of the arteries.) Plaque is made up of deposits of fatty substances, cholesterol, cellular waste products, calcium, and fibrin, and can develop in medium or large arteries.
The artery wall becomes thickened and looses its elasticity. Atherosclerosis is a disease of arterial blood vessels. Venous vessels are not involved unless surgically moved to function as an artery. Atherosclerosis is commonly referred to as a "hardening of blood vessels", but this is an over-simplification. Vascular lesions known as atheromatous plaques or atheromata (singular: atheroma) are formed in the vessel wall, and in late stages may reduce or restrict blood flow in the lumen. When the inner covering of an unstable atheroma breaks, compromising the structural integrity of the internal artery wall, the break may allow hemorrhage into the plaque, generate stenosis, embolism, (very rarely even hemorrhage beyond the artery wall), sometimes leading to severe morbidity and even death.
