Blood flowing through the vessels exerts pressure on the walls of these
vessels. This pressure is called blood pressure and is measured by the number
of millimeters that the blood causes a column of mercury to rise. We need two measurements
of pressure to identify the force of the blood flow: the pressure when the
heart beats and the pressure when it is resting between beats. The first is
called systolic and second diastolic. Typical resting systolic and diastolic
blood pressures are 120 and 80 mm Hg respectively.
