What is Atherosclerosis?
Atherosclerosis is a disease of the arteries. It is a term used to denote broader diseases of the arteries mainly coronary heart disease (CHD), peripheral arterial disease (PAD) and carotid artery disease (CAD). Atherosclerosis is caused by deposition of cholesterol in large arteries. The cholesterol that deposits limits the flow of blood to essential organs such as the heart or the brain leading to heart attacks or stroke respectively. More than 50% of people in the western countries die of atherosclerosis and is emerging as the number disease in the developing world. The risk factors of atherosclerosis includes; high fat diet, unhealthy lifestyle, lack of exercise, smoking, high blood pressure, diabetes and hereditary causes (such as familial hypercholesterolemia).
Pathogenesis of Atherosclerosis
It is now generally accepted that atherosclerosis is an inflammatory disorder. Any injury to the artery due to hemodynamic pressure (blood pressure), cigarette smoking, damage caused by viruses such as the Hepatitis B and C causes an inflammatory response. This then results in the release of monocyte chemoattractant protein (MCP) by endothelial cells lining the arteries. The monocytes at the site of inflammation release cytokines, chemokines and other mediators resulting in the differentiation of the monocytes to macrophages. Macrophages in turn express scavenger receptors at the cell surface causing them to engulf cholesterol from the plasma. This process leads to the formation of lipid laden "foam cells". A large number of foam cells leads to the formation of a plaque. These plaques release extracellular matrix such as collagen that causes the formation of fibrous plaques. Eventually the plaques become big and block the flow of blood. Eventually the plaque ruptures and this causes clinical complications such as heart attacks and stroke.