Large arteries like aorta and its branches have high elasticity. When blood is pumped into these vessels by heart during systole, the vessel expand to accomodate some excess blood temporarily. During diastole, when heart is not pumping, their elastic walls recoil and blood in them is propelled forward. These vessels are called windkessel vessel.
During ventricular diastole, although ventricular pressure falls very low, aorta is able to maintain diastole BP of 80mmHg.
During ventricular systole, it prevents too much rise in pressure
Atherosclerosis in old age leads to loss of windkessel effect causing systolic hypertension