Atherosclerosis (stiffening of the arteries) is usually associated with aging and can be accelerated by smoking. Because the blood vessels can no longer expand as needed when the blood tries to flow through, the result is increased pressure on the blood vessels (a.k.a high blood pressure!).
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Thanks for replying.
Why can the blood vessels no longer expand when the blood with high pressure tries to flow through?

the high pressure is exerting more physical force on the arteries, this can result in micro injury. The body reacts by applying cholesterol to the injured area.

Think of how a raging stream can act upon the stream bed, e.g.

Why can smoking lead to hypertension and atherosclerosis?
What part of the cigarette affects our body ? Why?