Chapter 19 Blood Vessels Lecture 4 Part 2b: Regulation of Blood Pressure Marieb’s Human Anatomy and Physiology Ninth Edition Marieb  Hoehn

2 Regulation of Blood Flow/Pressure Blood flow/pressure can be affected by 1) Autoregulation Local factors within tissue capillary beds Cause localized reaction 2) Neural mechanisms Responses to changes in arterial pressure or blood gas levels (baroreceptors or chemoreceptors) Cause more widespread changes VERY rapid 3) Endocrine mechanisms (will be covered with endocrine/urinary systems) Enhance short-term adjustments Direct long-term changes Work mainly through changes in blood volume

3 Autoregulation of Blood Flow/Pressure Local changes in response to metabolic needs of tissues Occurs at the level of the precapillary sphincters; not dependent on neural or hormonal mechanisms Changes in local blood flow may, or may not, necessitate activation of neural and/or hormonal mechanisms

4 Autoregulation of Blood Flow/Pressure Local vasodilators increase blood flow –Decreased O 2 (except pulmonary circulation) or increased CO 2 –Increase in lactic acid production –Histamine; release of nitric oxide (NO) –Increased K + or H + –Certain prostaglandins –Elevated local temperature Local vasoconstrictors decrease blood flow –Certain prostaglandins, thromboxanes (released by activated platelets and WBCs) –Endothelins released by damaged endothelial cells

5 Neural Control of Blood Pressure Controlling cardiac output and peripheral resistance regulates blood pressure Know this! Figure from: Hole’s Human A&P, 12 th edition, 2010

6 Neural Control of Blood Pressure If blood pressure rises, baroreceptors initiate the cardioinhibitory reflex, which lowers the blood pressure Know this! Figure from: Hole’s Human A&P, 12 th edition, 2010

7 Neural Control of Blood Pressure Dilating arterioles helps regulate (lower) blood pressure Know this! Figure from: Hole’s Human A&P, 12 th edition, 2010

8 Factors Affecting Blood Pressure (MAP) Contractility Afterload CVP CO HR SV ESV EDV ANS Parasympathetic Sympathetic MAP – Mean Arterial Pressure = Average effective pressure driving blood flow through the systemic organs **The MAP is dependent upon CO and TPR, i.e., MAP = CO x TPR TPR – Total Peripheral Resistance; depends upon *blood vessel radius, vessel length, blood viscosity, and turbulence MAP (BP)TPR 1/radius 4 ; Vessel length; Viscosity; Turbulence Figure adapted from: Aaronson & Ward, The Cardiovascular System at a Glance, Blackwell Publishing, 2007 = EDV - ESV = HR x SV

9 Factors Affecting Blood Pressure (MAP) MAP = X TPR 1 / radius 4 Vessel length Viscosity Turbulence Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

10 Review Factors influencing blood pressure –Cardiac output (CO) –Blood volume –Blood viscosity –Peripheral resistance (PR) Cardiovascular system function can be regulated by –Tissue autoregulation –Neural mechanisms –Endocrine mechanisms

11 Review Veins are a large reservoir of blood and exert a large effect upon blood pressure Venous blood flow depends upon –Skeletal muscle contraction –Breathing movement –Vasoconstriction of veins (venoconstriction) Central venous pressure is the pressure near the right atrium –If CVP increases, blood may back up –Increased CVP can lead to edema