If either of these occur and blocks the entire artery, a heart attack or stroke may result. Atherosclerosis affects large and medium-sized arteries. The type of artery and where plaque develops varies with .
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each person. It is a slow but growing disease that may start in childhood. In some people this disease progresses rapidly in their third decade. In others it doesn't become threatening until they"re in their fifties or sixties. Atherosclerosis is a very complex process. Exactly how it begins or what causes it is not known, but there are theories that have been proposed. Many scientists think atherosclerosis begins because the innermost layer of the artery becomes damaged. Three possible causes of damage to the arterial wall are: elevated levels of cholesterol and triglycerides in the blood, high blood pressure, and cigarette smoke. Cigarette smoke greatly aggravates and speeds up the growth of atherosclerosis in the coronary arteries, the aorta and arteries of the legs. Because of the damage, overtime fats, cholesterol, platelets, cellular debris and calcium are deposited into the artery wall. These substances may stimulate the cells in the innermost layer of the artery wall where the atherosclerotic lesions form. These cells accumulate, and many of them divide. At the same time, fat builds up within, and around .
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these cells, which also form connective tissues. The innermost layer of the artery becomes thickened by the accumulating cells and surrounding material. If the wall is thickened sufficiently, the diameter of the artery will be reduced and the amount of blood flowing in it is decreased, thus decreasing the oxygen supply. If the oxygen supply to the brain is cut off, a stroke can occur. And if the oxygen supply to the extremities occurs, gangrene can result. Often a blood clot forms and blocks the artery, stopping the flow of blood. .
High levels of the amino acids homocysteine and abnormal levels of protein-coated fats called lipoproteins also raise the risk of coronary artery disease.