BLOOD PRESSURE

 Blood Pressure and Rate of flow of Blood

It is the measure of force with which blood pushes up against the walls of blood vessels. It is the force that keeps blood flowing from the heart to all the capillary networks in the body. This pressure is generated by the contraction of ventricles (ventricle systole) and is the highest in aorta, then gradually reduces in arteries. The walls of arteries are elastic and the flow of blood stretches them, and it is felt as pulse. During diastole, the relaxation phase of the cardiac cycle, the heart is not exerting pressure on the blood in the arteries and pressure in them falls. The pressure reaches its high point during systole (systolic pressure which in normal individuals is 120 mm Hg) and its low point during diastole (diastolic pressure which in normal individuals ranges between 75-85) mmHg). The blood pressure gradually declines. The decline of the blood pressure in successive parts of systemic circuit, is the result of friction between the flowing blood and the walls of the blood vessels - thus blood moves from a region of higher pressure towards a region of lower pressure.

Several other changes occur along the route of blood flow. The difference between systolic and diastolic pressure continues to diminish until it disappears in the capillaries and veins.

The rate of blood flow tends to fall as the blood moves through the bra nching arteries and arterioles, the rate is lowest in the capillaries; and increases a gain in the venules and veins.

These changes in rate of blood flow result from changes in the total crosssectional area of the vessel system. The flow of blood in veins is maintained by the contraction of surrounding muscles and the action of semilunar valves which prevent back flow of blood. Muscular activity including breathing movements help normal flow of blood in the body.

Hypertension

It is a condition of high blood pressure. Prolonged high blood pressure damages the lining of the blood vessels and also leads to weakening of heart muscles (which have become thickened due to the continuous strain imposed on them), with declining efficiency of the pumping action of the heart. Blood may then be retained in the heart and lungs, often leading to fatal condition called congestive heart failure.