Blood Vessels and Blood Pressure
Blood pressureis the force exerted by circulating blood on the walls of blood vessels. The
contracting ventricles push blood out of the heart under force. The force of the contractions
put the blood under pressure. The pressure causes the walls of the arteries to move in a
rhythmic fashion. Blood in arteries is under the greatest amount of pressure. A person’s
pulse is the throbbing of their arteries that results from the heart beat.
The pressure of the circulating blood gradually decreases as blood moves from the arteries,
and into the smaller blood vessels. Blood that is in veins is not under pressure. The term
blood pressuregenerally refers to the pressure in the larger arteries that take blood away from
the heart. Arterial pressure results from the force that is applied to blood by the contracting
heart, where the blood “presses” against the walls of the arteries.
Thesystolicarterial pressure is the highest pressure in the arteries. Thediastolicarterial
pressure is the lowest pressure. Arterial pressure is most commonly measured by an in-
strument called asphygmomanometer,shown inFigure18.21. The height of a column of
mercury indicates the pressure of the circulating blood. Many modern blood pressure devices
no longer use mercury, but values are still reported in millimeters of mercury (mm Hg).
Figure 18.21: A digital sphygmomanometer is made of an inflatable cuff and a pressure
meter to measure blood pressure. ( 22 )
Healthy Blood Pressure Ranges
In the United States, the healthy ranges for arterial pressure are: