21-1 Anatomy and Physiology, Sixth Edition Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Chapter 21 Lecture Outline *

21-2 Chapter 21 Peripheral Circulation and Regulation

21-3 Peripheral Circulatory System Systemic vessels –Transport blood through most all body parts from left ventricle and back to right atrium Pulmonary vessels –Transport blood from right ventricle through lungs and back to left atrium Blood vessels and heart are regulated to ensure blood pressure is high enough for blood flow to meet metabolic needs of tissues

21-4 Blood Vessel Structure Arteries –Elastic, muscular, arterioles Capillaries –Blood flows from arterioles to capillaries –Most of exchange between blood and interstitial spaces occurs across the walls –Blood flows from capillaries to venous system Veins –Venules, small veins, medium or large veins

21-5 Capillaries Capillary wall consists mostly of endothelial cells Types classified by diameter/permeability –Continuous Do not have fenestrae –Fenestrated Have pores –Sinusoidal Large diameter with large fenestrae

21-6 Capillary Network Blood flows from arterioles through metarterioles, then through capillary network Venules drain network Smooth muscle in arterioles, metarterioles, precapillary sphincters regulates blood flow

21-7 Structure of Arteries and Veins Three layers except for capillaries and venules Tunica intima –Endothelium Tunica media –Vasoconstriction –Vasodilation Tunica adventitia –Merges with connective tissue surrounding blood vessels

21-8 Structure of Arteries Elastic or conducting arteries –Largest diameters, pressure high and fluctuates Muscular or medium arteries –Smooth muscle allows vessels to regulate blood supply by constricting or dilating Arterioles –Transport blood from small arteries to capillaries

21-9 Structure of Veins Venules and small veins –Tubes of endothelium on delicate basement membrane Medium and large veins Valves –Allow blood to flow toward heart but not in opposite direction Atriovenous anastomoses –Allow blood to flow from arterioles to small veins without passing through capillaries

21-10 Blood Vessel Comparison

21-11 Aging of the Arteries Arteriosclerosis –General term for degeneration changes in arteries making them less elastic Atherosclerosis –Deposition of plaque on walls

21-12 Dynamics of Blood Circulation Interrelationships between –Pressure –Flow –Resistance –Control mechanisms that regulate blood pressure –Blood flow through vessels

21-13 Laminar and Turbulent Flow Laminar flow –Streamlined –Outermost layer moving slowest and center moving fastest Turbulent flow –Interrupted –Rate of flow exceeds critical velocity –Fluid passes a constriction, sharp turn, rough surface

21-14 Blood Pressure Measure of force exerted by blood against the wall Blood moves through vessels because of blood pressure Measured by listening for Korotkoff sounds produced by turbulent flow in arteries as pressure released from blood pressure cuff

21-15 Blood Pressure Measurement

21-16 Blood Flow, Poiseuille’s Law and Viscosity Blood flow –Amount of blood moving through a vessel in a given time period –Directly proportional to pressure differences, inversely proportional to resistance Poiseuille’s Law –Flow decreases when resistance increases –Flow resistance decreases when vessel diameter increases Viscosity –Measure of resistance of liquid to flow –As viscosity increases, pressure required to flow increases

21-17 Critical Closing Pressure, Laplace’s Law and Compliance Critical closing pressure –Pressure at which a blood vessel collapses and blood flow stops Laplace’s Law –Force acting on blood vessel wall is proportional to diameter of the vessel times blood pressure Vascular compliance –Tendency for blood vessel volume to increase as blood pressure increases –More easily the vessel wall stretches, the greater its compliance –Venous system has a large compliance and acts as a blood reservoir

21-18 Physiology of Systemic Circulation Determined by –Anatomy of circulatory system –Dynamics of blood flow –Regulatory mechanisms that control heart and blood vessels Blood volume –Most in the veins –Smaller volumes in arteries and capillaries

21-19 Cross-Sectional Area As diameter of vessels decreases, the total cross-sectional area increases and velocity of blood flow decreases Much like a stream that flows rapidly through a narrow gorge but flows slowly through a broad plane

21-20 Pressure and Resistance Blood pressure averages 100 mm Hg in aorta and drops to 0 mm Hg in the right atrium Greatest drop in pressure occurs in arterioles which regulate blood flow through tissues No large fluctuations in capillaries and veins

21-21 Pulse Pressure Difference between systolic and diastolic pressures Increases when stroke volume increases or vascular compliance decreases Pulse pressure can be used to take a pulse to determine heart rate and rhythmicity

21-22 Capillary Exchange and Interstitial Fluid Volume Regulation Blood pressure, capillary permeability, and osmosis affect movement of fluid from capillaries A net movement of fluid occurs from blood into tissues. Fluid gained by tissues is removed by lymphatic system.

21-23 Fluid Exchange Across Capillary Walls

21-24 Vein Characteristics and Effect of Gravity on Blood Pressure Vein Characteristics Venous return to heart increases due to increase in blood volume, venous tone, and arteriole dilation Effect of Gravity In a standing position, hydrostatic pressure caused by gravity increases blood pressure below the heart and decreases pressure above the heart

21-25 Control of Blood Flow by Tissues Local control –In most tissues, blood flow is proportional to metabolic needs of tissues Nervous System –Responsible for routing blood flow and maintaining blood pressure Hormonal Control –Sympathetic action potentials stimulate epinephrine and norepinephrine

21-26 Local Control of Blood Flow by Tissues Blood flow can increase 7-8 times as a result of vasodilation of metarterioles and precapillary sphincters in response to increased rate of metabolism –Vasodilator substances produced as metabolism increases –Vasomotion is periodic contraction and relaxation of precapillary sphincters

21-27 Nervous Regulation of Blood Vessels

21-28 Short-Term Regulation of Blood Pressure Baroreceptor reflexes –Change peripheral resistance, heart rate, and stroke volume in response to changes in blood pressure Chemoreceptor reflexes –Sensory receptors sensitive to oxygen, carbon dioxide, and pH levels of blood Central nervous system ischemic response –Results from high carbon dioxide or low pH levels in medulla and increases peripheral resistance

21-29 Baroreceptor Reflex Control

21-30 Chemoreceptor Reflex Control

21-31 Long-Term Regulation of Blood Pressure Renin-angiotensin-aldosterone mechanism Vasopressin (ADH) mechanism Atrial natriuretic mechanism Fluid shift mechanism Stress-relaxation response

21-32 Renin-Angiotensin-Aldosterone Mechanism

21-33 Vasopressin (ADH) Mechanism

21-34 Long Term Mechanisms Atrial natriuretic –Hormone released from cardiac muscle cells when atrial blood pressure increases, simulating an increase in urinary production, causing a decrease in blood volume and blood pressure Fluid shift –Movement of fluid from interstitial spaces into capillaries in response to decrease in blood pressure to maintain blood volume Stress-relaxation –Adjustment of blood vessel smooth muscle to respond to change in blood volume

21-35 Shock Inadequate blood flow throughout body Three stages –Compensated: Blood pressure decreases only a moderate amount and mechanisms able to reestablish normal blood pressure and flow –Progressive: Compensatory mechanisms inadequate and positive feedback cycle develops; cycle proceeds to next stage or medical treatment reestablishes adequate blood flow to tissues –Irreversible: Leads to death, regardless of medical treatment