Which condition causes plaque to accumulate on the walls of the arteries which makes them thicken and lose elasticity

The correct answer is Atherosclerosis. What this disease does is create layers of white blood calls and fibrofatty tissue to make the arteries thicken. This also includes things like triglycerides and cholesterol. This increases blood pressure and can sometimes be deadly for people, but it is usually noticed way after it establishes itself.