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What is Atherosclerosis? - Definition, Symptoms & Treatment

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Atherosclerosis is a disease that is silent, but often deadly, since it can cause you to suddenly have a heart attack or stroke. In this lesson, we will learn how atherosclerosis develops and what you can do to prevent it.

What is Atherosclerosis?

Because heart disease is the leading cause of death in this country, and millions of people are affected by it every day, it's likely that you know someone who has had a heart attack or stroke. Both heart attacks and strokes are usually caused by an underlying disorder called atherosclerosis. Atherosclerosis occurs when something called plaque builds up in the walls of your arteries. Plaque contains fat, cholesterol, calcium, and white blood cells. It can lead to a heart attack or stroke if the plaque ruptures and forms a clot that cuts off the blood supply to the heart (in a heart attack) or the brain (in a stroke). Although heart attack and stroke are the most common conditions that result from atherosclerosis, it can affect any arteries in the body, and so is responsible for other diseases as well, such as chronic kidney disease and peripheral artery disease.

On the left, a normal, healthy artery has thin walls and blood can flow through it easily. On the right, atherosclerosis has caused a plaque to develop in the artery wall that stretches it out and limits the amount of blood that can pass through the artery.
plaque in artery

How Does an Atherosclerotic Plaque Form?

Atherosclerotic plaque begins to form very early in life, when you are only a baby or young child, but it grows very slowly and most people do not know they have it until at least middle age. It starts simply when tiny cholesterol and fat particles that are floating in your blood stick to the walls of your arteries and somehow move out of the bloodstream and into the artery walls. No one really knows why this happens, but it seems to depend on both genetic and lifestyle factors, such as your diet and how much you exercise. At this point, the plaque looks like a small white streak on the artery wall and it is unlikely to cause any problems. Although you probably haven't thought much about it, you almost certainly have these early plaques in your arteries right now. They have been found inside the arteries of babies less than a year old, and by the teenage years, significant amounts of plaque are usually present.

The presence of cholesterol particles inside the wall of the artery triggers an immune response because your body thinks that they are potential invaders that need to be destroyed. White blood cells come in and try to remove the cholesterol, but more comes in all the time and it becomes a chronic cycle of inflammation. Over time, the plaque grows as the artery wall fills up with cholesterol and white blood cells, and often a hard shell of calcium forms over the top of the plaque. The wall of the artery can stretch for a while, but if the plaque continues to grow, it will start to invade the space inside the artery and cause the artery to narrow. When the artery becomes so narrow that blood flow through it is significantly reduced, you will begin to suffer symptoms such as pain and shortness of breath. Because plaques grow so slowly, people do not usually have any symptoms until 40-60 years of age, and many people who have large plaques will never have any symptoms at all.

Atherosclerosis begins early in life as cholesterol particles become trapped in the walls of arteries. Over time, white blood cells come in and inflammation causes the plaque to grow. Eventually, it can rupture and cause a heart attack or stroke.
progression of atherosclerosis

What Happens When a Plaque Ruptures?

Although most teenagers and adults (even you!) have some plaques in their arteries, some people will never know they have them, while others will have heart attacks or strokes at age 40 (or even earlier). What happens to the plaque to cause a heart attack or stroke, and why doesn't this happen to everyone? When plaques are small, they rarely cause any problems, but as they grow, they become more unstable and prone to rupture. When the plaque ruptures, pieces of it break away, and these pieces can travel to smaller arteries where they can block blood flow completely and cause the tissues that are supplied by that artery to die. When this happens in the coronary arteries, it causes a heart attack, and when it happens in the arteries of the brain, it causes a stroke. It seems that some people are more prone to develop unstable plaques than others, and this is primarily an inherited tendency. This is why some people will develop clinical symptoms, like heart attacks and strokes, while others with similar amounts of plaque, will not.

When a plaque ruptures, it can cause a blood clot that completely cuts off blood flow through an artery. This is what happens when you have a heart attack or stroke.
blood clot causes heart attack

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