Atherosclerosis is caused due to the hardening of large or medium sized arteries. This hardening of arteries happens as a result of the deposition of cholesterol, fatty substances, calcium, fibrin and other cellular waste products in their inner lining. But it does not happen all of a sudden. Rather it is a whole process and takes time. It usually starts in childhood and becomes noticeable only in 50s or 60s.
The heart brain and other parts of the body get oxygenated blood through the arteries. Arteries are made of endothelium or inner lining. In the condition of atherosclerosis these inner linings are damaged due to high level of cholesterol, high blood pressure, smoking, diabetes and high triglycerides. Once these inner linings are damaged, substances like calcium, cellular waste, fats, cholesterol are deposited in the wall of the arteries.
In the long run, it takes a shape of plaques. As a result of the formation these plaques, walls of these arteries get hardened, narrowed, or even blocked. Moreover the formation of plaques may also give rise to two new conditions. First, there may occur bleeding in the plaque. Secondly, plaque surface may develop thrombus or blood clottings. In any of these two cases artery may get blocked and patient may suffer from heart attack or stroke.
It is said that hardening of blood vessels is a kind of response to the damaged endothelium from smoking, high cholesterol and high blood pressure and such other conditions. An individual with all these risk factors is more likely to develop atherosclerosis than the other having no such risk factors.
Less physical activity, diabetes and overweight are some other risk factors for this disease.
In case of coronary artery disease high level of lipoproteins increases the risk more. But high density lipoproteins in the blood vessel make you less prone to the atherosclerosis. In the formation of atherosclerotic plaques, triglycerides play a part though it is still not clear or proved. All these risk factors can be modified to reduce the chances of the impairment of blood flow. But age, sex and heredity are some non-modifiable risk factors. A patient just can not have control over them.