Atherosclerosis
Atherosclerosis, also known as arteriosclerosis or "hardening of the arteries", is a disease process that causes narrowing of the arteries and thickening of the artery walls. It occurs to some extent in most people as they get older, but more rapidly in some for reasons which are largely preventable. It is caused by build-up of deposits such as cholesterol accompanied by fibrous tissue and calcification.Since arteries carry mainly oxygenated blood from the heart to the tissues, including the heart muscle itself, this can result in serious medical problems such as heart attack or stroke. Atherosclerosis also predisposes towards the formation of a blood clot or thrombus that is often the precipitating cause of the acute event. Atherosclerosis is the major cause of death and disability in First World nations and is an increasing problem in many newly developing countries.
There is no cure for atherosclerosis though surgery and related procedures can relieve blockages in specific places. The major treatment goal is to reduce progression and complications when atherosclerosis has already presented clinically. However, it is better to prevent the development of significant atherosclerotic disease in the first place. Lifestyle changes such as healthy diet and exercise can help lower risk for the disease.
What is atherosclerosis?
Atherosclerosis is best described by its clinical consequences.Clinical consequences
Atherosclerosis is the underlying medical problem in most patients who develop the following illnesses:- Coronary artery disease (coronary heart disease): occurs when atherosclerosis narrows the coronary arteries (arteries supplying blood to the heart muscle). As the coronary arteries narrow, angina (chest pain) may result especially on exertion. The risk of heart attack also increases, often due to the formation of a thrombus over the atherosclerotic area. In a heart attack a portion of the heart muscle actually dies; the technical term is ‘myocardial infarction’. If this occurs very suddenly and rapidly it is called an acute myocardial infarction.
- Stroke: a thrombus may form in an artery to the brain that has been narrowed by atherosclerosis, or a piece of atherosclerotic plaque in an artery supplying the brain can break off to form an embolus (blockage), or the weakened arterial wall may rupture and bleed. The end result in all cases is greater or lesser damage to the brain which presents as a stroke.
- Peripheral arterial disease: atherosclerosis can narrow the major arteries to the legs. The resultant reduced blood flow may cause a crampy leg pain during exercise which is called intermittent claudication. If blood flow is severely restricted, parts of the leg may become pale or "blue" (cyanotic), feel cool and develop skin sores and ulcers or even gangrene (tissue death).
- Abdominal angina and bowel infarction: when atherosclerosis narrows arteries that supply blood to the intestines, this causes abdominal pain called abdominal angina. Blockage of intestinal blood supply causes a bowel infarction: this is similar to a myocardial infarction, but involves the intestines instead of the heart.
- Other conditions: Atherosclerosis may contribute to the development of an aortic aneurysm (a weakening and "ballooning" of the aorta, the main artery leading from the heart) or in renal artery stenosis (narrowing of the kidney arteries). An aneurysm may rupture causing a massive haemorrhage or bleed. Narrowing of renal arteries can reduce kidney function and occasionally cause high blood pressure.
What causes atherosclerosis?
Arterial narrowing is caused by the formation of "plaques", or areas of abnormality and thickening in the wall of an artery. These begin as thin, fatty streaks in the inner portion of an arterial wall. In a healthy young person the streaks may come and go.But if arteries are damaged - from high blood pressure or smoking or excess cholesterol and related fatty substances, for example - the inner lining of the wall can start to deteriorate. This sets in motion the series of events described below which create a fully-fledged atherosclerotic plaque.
Over time, various substances such as fats, cholesterol, platelets (particles that cause blood clotting) and cellular debris are deposited at these sites. Eventually, scar tissue and sometimes calcium crystals surround the fatty plaque, making the arteries hard and inelastic.
As a plaque grows, it produces a rough area in the artery's normally smooth inner surface. This rough area can trigger the formation of a thrombus, decreasing and eventually blocking blood flow in the artery. Large amounts of excess fat also accumulate in the wall which is liable to rupture into the lumen of the artery. This also causes clotting. Portions of the plaque may break off to deposit emboli in arteries supplying the brain particularly, and elsewhere in the body.
Through any of these processes the affected tissue is then starved of blood and oxygen with the result that the cells may die or become severely damaged.
Development of a plaque also deforms the arterial wall, increasing turbulence and resistance to blood flow. As resistance to flow increases, blood pressure increases. Therefore, the heart has to work harder to pump blood, causing it to enlarge. This may lead to abnormalities of heart action and ultimately heart failure. High blood pressure also has deleterious effects on cerebral arteries and the small arteries to the eyes and kidneys resulting in failure of these organs.
Who gets atherosclerosis and what are the risk factors?
Atherosclerosis is the major cause of death and disability in First World nations through the clinical mechanisms described above. Coronary artery disease and its complications, together with stroke, are responsible for more deaths than all other causes combined.There is also an emerging epidemic of heart attacks in Africa and other Third World countries as more people adopt aspects of the sedentary western lifestyle including a high-fat, high-cholesterol diet. Heart disease is one of the leading causes of premature death in South Africa, notably in the white and Indian communities but increasingly in the black population.
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