27Resistance Resistance – opposition to flow Measure of the amount of friction blood encounters as it passes through vesselsGenerally encountered in the systemic circulationReferred to as peripheral resistance (PR)The three important sources of resistance are blood viscosity, total blood vessel length, and blood vessel diameter
28Resistance Factors: Viscosity and Vessel Length Resistance factors that remain relatively constant are:Blood viscosity – thickness or “stickiness” of the bloodBlood vessel length – the longer the vessel, the greater the resistance encountered
43Venous Blood PressureVenous BP is steady and changes little during the cardiac cycleThe pressure gradient in the venous system is only about 20 mm HgA cut vein has even blood flow; a lacerated artery flows in spurts
57Circulatory ShockCirculatory shock – any condition in which blood vessels are inadequately filled and blood cannot circulate normallyResults in inadequate blood flow to meet tissue needsThree types include:Hypovolemic shockVascular shockCardiogenic shock
70Thought Questions Take Home Exam Extra Credit What are some of the methods of treating high blood pressure and how do they affect blood pressure?Why do they recommend exercise to decrease high blood pressure?
71Summary Cardiac Cycle Cardiac Output Fetal Circulation Blood Vessels Stroke VolumeHeart RateFetal CirculationBlood VesselsBlood FlowBlood PressureCirculatory System Response to Exercise