The heart, as we have learned, is a pump that sends the blood circulating through our body. The pumping action takes place when the left ventricle of the heart contracts. This forces the blood out into the arteries, which expand to receive the oncoming blood.

But the arteries have a muscular lining which resists this pressure, and thus the blood is squeezed out of them into the smaller vessels of the body. Blood pressure is the amount of pressure on the blood as a result of the heart’s pumping and the resistance of the arterial walls.