Blood pressure and Rate of blood flow I Chapter 14 Biology I F.Sc First Year Lec # 32

#biology11class #biologyfirstyear #FSc #chapter14 #Transport Like Our Facebook page. -----------------------------------   / bismacademy   ------------------------------------ Blood Pressure and Rate of flow. Definition. It is the measure of force with which blood pushes up against the walls of blood vessels. Importance. It is the force that keeps blood flowing from the heart to all the capillary networks in the body. Ventricle systole This pressure is generated by the contraction of ventricles (ventricle systole) and is the highest in aorta, then gradually reduces in arteries. Pulse. 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. Diastolic and Systolic values. 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 mm Hg). Decline in BP . 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. Other changes. Several other changes occur along the route of blood flow. i) Difference between systolic and diastolic pressure continues to diminish until it disappears in the capillaries and veins. ii) Rate of blood flow tends to fall as the blood moves through the branching arteries and arterioles, the rate are lowest in the capillaries; and increases again in the venules and veins. Importance. These changes in rate of blood flow result from changes in the total cross sectional area of the vessel system. Flow in veins. 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.