Blood Pressure

blood pressure is the pressure blood on the walls of the circulatory system. Blood pressure depends on two factors… 1.cardiac output - -any increase in the amount of blood pumped from the heart each minute will increase blood pressure -loss of blood decreases blood pressure. 2.arteriolar resistance – -if the diameter of the artery or arteriole is reduced, less blood can flow through – therefore blood pressure increases. -arteriolar dilation increases blood flow from the arterioles reducing blood pressure.

Other Factors Affecting Blood Pressure Heart Rate: * faster heart rate, results in greater pressure on the blood vessels Cholesterol and Fat Deposits: * decreases the inside diameter of the vessels, more resistance occurs, resulting in increased pressure. This is referred to as atherosclerosis Viscosity of the Blood: * thick blood flows less readily * viscosity depends on the number of RBCs compared to the plasma

Hypertension Blood pressures consistently above the normal levels result in a condition called hypertension, commonly known as high blood pressure. Hypertension is dangerous because it forces the heart to work harder to pump blood around the body. Often there are no symptoms until a serious event, such as a heart attack or stroke occurs. Blood pressure is measured with an instrument called a sphygmomanometer.

Blood pressure is measured as systolic pressure over diastolic pressure. Normal blood pressure for teenagers is approximately 120/80. The units for blood pressure are mm Hg (millimetres of mercury)