Blood pressure is a force
originating when the heart's pumping pushes the blood
against the walls of the blood vessels.
Their stretching and contraction help maintain blood
flow. Usually measured over an arm or leg artery in
humans, blood pressure is expressed as two numbers;
normal adult blood pressure is about 120/80 mm of mercury.
The higher number (systolic) is measured when the heart's
ventricles contract and the lower (diastolic) when they
relax. |