Atherosclerosis is a form of arteriosclerosis in which plaque builds up in the inner linings of the arteries (What). Plaque consists of a combination of fatty substances, cholesterol, waste products from cells, fibrin and calcium and usually develops in medium and large arteries, thickening their walls and causing them to lose elasticity and so become less resilient. Atheromatous plaques build up in vessel walls and in advanced stages, reduce or restrict blood flow through the vessel lumen. The inner covering of the atheroma may break, compromising the integrity of the internal artery wall, allowing hemorrhage into the plaque and generating stenosis or embolism, which can lead to morbidity and even death.
It is believed that atherosclerosis is caused by a response to damage to the arterial endothelium which can result from high cholesterol levels, high blood pressure, and cigarette smoking (What). When there is damage to the arterial wall, an inflammatory response occurs and monocytes enter the arterial wall, becoming macrophages in the tissue. These macrophages ingest oxidized cholesterol, becoming foam cells, so called because of the numerous vesicles of lipid they contain. These give the appearance of fatty streaks in the vessel wall. The foam cells die out and the inflammatory response continues, with intracellular microcalcification of the smooth muscle cells adjacent to the atheroma. As cells die, extracellular calcium deposits occur between the muscular wall and the outer portion of the atheromatous plaque.
Cholesterol comes to the arterial wall in the form of LDL particles, which can pass through the intercellular gaps between the intima lining cells (What). Cholesterol is released from the LDL particles and attracts macrophages, which move it into HDL particles to avoid becoming foam cells and dying. A fibrous protective cap forms between the fatty deposits and the arterial intima. The atheroma produces...