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Narrator: This condition is a process in which deposits of fatty material, called plaque, build up inside the walls of arteries, reducing or completely blocking blood flow.Although the exact causes of atherosclerosis are not clear, many scientists think it begins with damage to the inner wall of an artery, called the endothelium.Substances traveling in the blood, such as cholesterol, fats and cellular waste products accumulate inside the damaged area of the arterial wall.Chemical reactions occurring within the buildup of material cause cholesterol molecules to oxidize.This initiates an inflammatory response in which the endothelial cells at the damage site release chemicals that signal a call for help.In response, monocyctes from the blood stream travel to the damage site. Stimulation from oxidized cholesterol converts the monocytes into macrophages.The macrophages eat and digest the cholesterol molecules. As a result of this process, the macrophages change into foam cells, which accumulate to form plaque.As the plaque increases in size, the arterial wall thickens and hardens.At the same time, smooth muscle cells within the arterial wall begin to multiply.Most of the smooth muscle cells move to the surface of the plaque.These cells contribute to the formation of a firm, fibrous cap covering the plaque.Eventually the passageway through the artery narrows enough to reduce blood flow and the amount of oxygen received by the organs it supplies.Over time the cap may erode and break open, releasing plaque into the bloodstream. The plaque can flow downstream and contribute to the formation of a blood clot, which can stop blood flow.As a result, limited blood supply is available to the area surrounding the partially blocked artery, degrading and potentially killing the neighboring tissue.