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.
Atherosclerosis typically begins in later childhood, is usually found in most major arteries, yet is asymptomatic and not detected by most diagnostic methods during life. It most commonly becomes seriously symptomatic when interfering with the coronary circulation supplying the heart or cerebral circulation supplying the brain, and is considered the most important underlying cause of strokes, heart attacks, various heart diseases including congestive heart failure and most cardiovascular diseases in general.
Atherosclerosis is the major cause of death and disability in industrialized nations, including the United States. This is because atherosclerosis is the underlying medical problem in most patients with any of the following illnesses:
Coronary artery disease - In this chronic disease, atherosclerosis narrows the coronary arteries, the arteries supplying blood to the heart muscle. As the coronary arteries narrow, the chest pain called angina may be triggered. And the risk of a heart attack (myocardial infarction), which occurs when a coronary artery is blocked completely, is increased. Coronary artery disease currently affects 11 million people in the United States.
Stroke - A blood clot (thrombus) may form inside a brain artery that has been narrowed by atherosclerosis. Once this thrombus forms, it cuts off the blood supply to part of the brain, causing a thrombotic stroke. Currently, about 75 percent of strokes in industrialized countries are thrombotic strokes.
Abdominal angina and bowel infarction - When atherosclerosis narrows arteries that supply blood to the intestines, it causes a form of abdominal pain called abdominal angina. Complete, sudden blockage of intestinal blood supply can cause a bowel infarction. A bowel infarction is similar to a heart attack, but it involves the intestines rather than the heart.
Atherosclerosis of the extremities - Atherosclerosis can narrow the major arteries that supply blood to the legs, especially the femoral and popliteal arteries. These two arteries are affected in 80 percent to 90 percent of people with this problem. The reduced blood flow to the legs may result in a crampy leg pain during exercise called intermittent claudication. If blood flow is compromised severely, parts of the leg may become pale or cyanotic (turn blue), feel cold to the touch and eventually develop gangrene.
Other conditions - Atherosclerosis may be a factor in the development of an aortic aneurysm or renal artery stenosis (narrowing of the kidney arteries).