The Probert Encyclopaedia of Medicine

ATHEROSCLEROSIS

Atherosclerosis is a form of arteriosclerosis. Atherosclerosis is the hardening of the arteries caused by cholesterol plaque deposits. It can occur in the coronary arteries, the carotid arteries, the aorta, and the leg arteries. Healthy arteries are flexible, strong, and elastic. The inner layer, the tunica interna, is smooth, enabling blood to flow freely. As a person ages, the arteries normally become thicker and less elastic, and their calcium content increases. This natural ' hardening' process occurs throughout the artery system.

Atherosclerosis, by contrast, affects only the larger arteries. As the plaque builds up, the inner layers of the artery walls become thick and irregular. Fat, cholesterol, and other materials accumulate in certain areas. This gradual build-up over a long period of time reduced the circulation of blood and increases the risk of heart attack, stroke, and other serious arterial diseases. A person having atherosclerosis will often experience symptoms of angina, stroke, and claudication. All of the symptoms are caused by insufficient blood flow due to atherosclerosis. Initially, the deposits of fat-containing cells that lead to atherosclerosis are only slight streaks, and are called fatty streaks. As the fatty streaks enlarge, they invade the deeper layers of the artery walls, causing scarring and calcium deposits. Large deposits are called athermas or plaques. The plaques calcify into a chalky substance. The plaque consists of a firm shell that contains calcium with areas of fatty material, and a centre consisting of soft cholesterol. As the plaque deposits grow the cardiac muscle beyond the blockage becomes deprived of blood, a condition known as myocardial ischemia. The healthy elastic wall of the artery changes into dead and unresponsive scar tissue. If insufficient blood flow continues, the cardiac muscle dies, causing myocardial infarction. As the degeneration of the endothelial lining of the arteries continues, the lining may be damaged. Blood platelets stick to the site of injury, and a chemical signal is activated that promotes an influx of cholesterol.

The symptoms of atherosclerosis develop slowly as the development of the occlusion of the arteries progresses. Symptoms include angina, stroke, and claudication. The specific symptoms depend on which artery or arteries are occluded. If the leg arteries are affected, symptoms usually include numbness, fatigue, or pain in the leg. Occlusion of the coronary arteries may lead to angina or even a heart attack. When atherosclerosis occurs in the coronary arteries, it can lead to myocardial ischemia, an insufficient flow of blood to the heart. If the duration of ischemia is brief, the damage is reversible. However, if the duration of ischemia is longer than 40 to 60 minutes, irreversible damage may occur, and the parts of the heart muscle deprived of blood become permanently damaged, leading to myocardial infarction. Other commonly affected large arteries include the carotid arteries and the abdominal aorta. Initially, the symptoms of atherosclerosis are more likely to occur during exercise or strenuous activity than at rest. The symptoms develop during exercise because the arteries cannot supply the muscles with enough oxygen and nutrients. This process results in the build-up of by-products in the muscle that cannot be removed efficiently because of the occluded blood flow. This build-up of waste products, such as lactic acid, causes pain. It is similar to the build-up of lactic acid in muscles due to overexertion. As the narrowing of the arteries increases, the symptoms become prevalent with less and less exertion. The symptoms generally disappear after a few minutes of rest. However, the occlusion can be so severe that even the resting muscle does not get enough blood flow and the symptoms may be experienced even when sitting still.
Research Atherosclerosis