How does atherosclerosis happen? continued...
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.
Plaques are covered with a fibrous cap, which may rupture if some trigger causes a surge in blood pressure or causes the artery to constrict. A person may have a heart attack if a plaque breaks open, creating a blood clot that completely blocks blood flow through the artery.
Complicated lesion. The last stage of atherosclerosis occurs when the plaque breaks
open, exposing the cholesterol and tissue underneath. Blood clots form in
response to this rupture and cause symptoms of a heart attack and unstable
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.
Injury may stimulate cells to grow and divide as part of the
inflammatory process. This normal, healing response to chronic injury may
actually result in the growth of atherosclerotic plaque.
This injury could be caused by any number of things, including:
- Physical stress on the artery lining, such as
stress caused by
high blood pressure.
- A response to an
infection within the artery wall.
- Oxidative damage to the artery
lining. Oxidative damage refers to injury caused by unstable molecules called
free radicals. Free radicals are formed during reactions between oxygen and LDL
("bad" or low-density lipoprotein) cholesterol.
- Oxidized LDL
cholesterol may cause injury to the blood vessel wall and promote an
inflammatory reaction that clogs the artery lining with debris. But exactly why high
cholesterol levels promote plaque formation is not clear. Cholesterol is found
normally in all cell membranes, but it may alter the physical properties of the
blood vessel wall, making it more likely to get damaged.
How smoking leads to atherosclerosis
Smoking plays a large role in the development of atherosclerosis. The
carbon monoxide and nicotine contained in tobacco smoke affect blood flow
through your arteries by:
- Making it easier for cholesterol-carrying
lipoproteins to enter the walls of your arteries.
- Promoting the
formation of fibrous plaque.
- Promoting the formation of blood
clots that can completely block your arteries.