Blood Pressure

Human Physiology

Lesson 32 : Blood Vessels & Lymphatic System

Blood Pressure

Blood Pressure: is defined as a physical force/pressure exerted by circulating blood on the wall of blood vessels. The pressure can be demonstrated easily in a hose pipe used in the gardens for watering. The water flowing through a hose pipe also exerts similar pressure on the rubber tubing wall that becomes evident when the wall is punctured. When a small hole is created in the wall, the water flow out through this hole in the form of a fountain, the height of fountain depends upon the quantum of pressure inside conduit, Blood pressure is allows the blood to circulates through various blood vessels since as a fluid, the blood always flows along a pressure gradient. Pressure is highest in left ventricle followed by arteries, arterioles, capillaries, venules and lowest in veins and right atrium. Blood pressure is measured in mm Hg unit.

Blood pressure in arteries is of biphasic nature and fluctuates with every heart beat. The pressure is higher at the time of cardiac systole (heart contraction) at about 120 mm Hg and it is termed as systolic blood pressure. The pressure in the arteries tends to be lower at the time of cardiac diastole (heart relaxation) at about 80 mm Hg and it is termed as diastolic blood pressure. The difference between systolic and diastolic blood pressure is known as pulse pressure. This pressure fluctuation in the arteries is responsible for pulsation in the arteries. One systole followed by diastole comprises of one pulse and pulse rate is defined as number of pulses recorded in one minute time. Pulse rate normally coincides with heart rate under physiological conditions. Pulse rate tends to be higher in fever, stress, excitement, heart exposure etc. and it tends to decline during cold exposure, depression etc. Pulse rate in adult human is 70-80 beats per minute. It is lower in individuals of older age and higher in young ones. Pulsation is absent in veins and capillaries. Common instruments used to record blood pressure is sphygmomanometer (mercury (Fig 32b)/aneroid/digital or electronic type).


Last modified: Tuesday, 10 April 2012, 12:29 PM