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Atherosclerosis - Topic Overview

How does atherosclerosis happen?

Although the exact process is not completely understood, scientists have described three different stages of atherosclerosis that lead to clogged arteries. These stages do not necessarily occur in order, nor is there always a progression from one stage to the next.

The fatty streak. The "fatty streak" appears as a yellow streak running inside the walls of the major arteries, such as the aorta. The streak consists of cholesterol, white blood cells, and other cellular matter. The fatty streak by itself does not cause symptoms of heart disease but can develop into a more advanced form of atherosclerosis, called fibrous plaque.

The plaque. A plaque forms in the inner layer of the artery. Plaque is a buildup of cholesterol, white blood cells, calcium, and other substances in the walls of arteries. Over time, plaque narrows the artery, and the artery hardens.

Plaque sometimes reduces blood flow to the heart muscle, which can cause angina symptoms. Plaque in the large artery in the neck (carotid artery stenosis) may block blood flow to the brain and is a common cause of transient ischemic attack (sometimes called "mini-stroke") and stroke.

Stable and unstable plaque. Plaques are defined based on the risk that they will tear or rupture. Stable plaque is less likely to rupture. These plaques have a thick fibrous cap and are made up of substances that are stable and not likely to rupture. Unstable plaque is more likely to rupture. These plaques have a thin fibrous cap and are made up of substances like fats that can expand. Inflammation within the plaque can make the fibrous cap unstable and more likely to tear apart.

Blocked artery. A blockage in the artery can happen if the plaque tears or ruptures. This rupture exposes the cholesterol and tissue that was under the fibrous cap. Blood clots form in response to this rupture. The blood clot blocks the blood flow in the artery. This can cause a heart attack or stroke.

Why does atherosclerosis happen?

Response-to-injury. This theory suggests that atherosclerosis develops as a result of repetitive injury to the inner lining of the artery.

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