What is the difference between arteriosclerosis and atherosclerosis? Why are both conditions a health threat?

What is the difference between arteriosclerosis and atherosclerosis? Why are both conditions a health threat?

Arteriosclerosis: a condition that occurs when the walls of the arterioles thicken, with loss of elasticity and contractility.

Atherosclerosis: a thickening and hardening of the arteries that occurs when plaques of cholesterol and lipids form in the arterial tunica intima.