Chapter 15 Blood Flow and the Control of Blood Pressure 2013 Pearson Education Inc About This Chapter The blood vessels Blood pressure Resistance in the arterioles Distribution of blood to the tissues Regulation of cardiovascular function Exchange at the capillaries The lymphatic system Cardiovascular disease 2013 Pearson Education Inc Figure 15 12 DISTRIBUTION OF BLOOD IN THE BODY AT REST Blood flow to the major organs is represented in three ways as a percentage of total flow as volume per 100 grams of tissue per minute and as an absolute rate of flow in L min 100 of cardiac output Right heart Cardiac output 5 0 L min Lungs 14 Left heart 0 70 L min Brain 55 mL 100 g min 0 20 L min 4 Heart 70 mL 100 g min 27 Liver and digestive tract 1 35 L min 100 mL 100 g min 20 1 00 L min Kidneys 400 mL 100 g min 21 Skeletal muscle 1 05 L min 5 mL 100 g min 5 0 25 L min Skin 10 mL 100 g min 9 Bone and other tissues 3 mL 100 g min FIGURE QUESTION What is the rate of blood flow through the lungs 0 45 L min Figure 15 2 BLOOD VESSEL STRUCTURE Artery 4 0 mm 1 0 mm Arteriole 30 0 m 6 0 m Capillary 8 0 m 0 5 m Venule 20 0 m Vein 5 0 mm 0 5 mm 1 0 m m Elas tic t issu e S mo o th mus cl e Fibro us ti ssue eliu End oth Mean wall t hickn ess Mea n dia mete r The walls of blood vessels vary in diameter and composition The bars show the relative proportions of the different tissues The endothelium and its underlying elastic tissue together form the tunica intima Adapted from A C Burton Physiol Rev 34 619 642 1954 Figure 15 1 FUNCTIONAL MODEL OF THE CARDIOVASCULAR SYSTEM This functional model of the cardiovascular system shows the heart and blood vessels as a single closed loop The elastic systemic arteries are a pressure reservoir that maintains blood flow during ventricular relaxation Functions shown in red Aorta Aortic valve Left heart Left ventricle Mitral valve Left atrium The arterioles shown with adjustable screws that alter their diameter are the site of variable resistance Pulmonary veins Each side of the heart functions as an independent pump Lungs Capillaries Pulmonary artery Pulmonary valve Right ventricle Right heart Tricuspid valve Right atrium Venae cavae Valves in veins and heart assure one way flow around the closed loop system Exchange between the blood and cells takes place at the capillaries Systemic veins serve as an expandable volume reservoir Venules Postcapillary venules participate in exchange and support leukocyte adhesion and emigration FIGURE QUESTION Are pumps in this model operating in parallel or in series Figure 15 5a Ventricular contraction Contraction of the ventricles pushes blood into the elastic arteries causing them to stretch Aorta and arteries Aorta and arteries expand and store pressure in elastic walls Semilunar valve opens Blood ejected from ventricles flows into the arteries Ventricle Ventricle contracts Figure 15 5b Ventricular relaxation Elastic recoil in the arteries maintains driving pressure during ventricular diastole Elastic recoil of arteries sends blood forward into rest of circulatory system Semilunar valve shuts preventing flow back into ventricle Ventricle Isovolumic ventricular relaxation Figure 15 6 SYSTEMIC CIRCULATION PRESSURES Pressure waves created by ventricular contraction travel into the blood vessels Pressure in the arterial side of the circulation cycles but the pressure waves diminish in amplitude with distance and disappear at the capillaries Systolic pressure Pressure mm Hg 120 Pulse pressure 100 80 60 40 Diastolic pressure Mean arterial pressure 20 Left Arteries Arterioles Capillaries ventricle Venules veins Right atrium Table 15 1 Pressure Flow and Resistance in the Cardiovascular System Figure 15 3a 1 of 4 The microcirculation Collateral arteries Vein Venule Arteriole wall is smooth muscle Precapillary sphincters can close off capillaries in response to local signals Capillaries Metarterioles can act as bypass channels Small venule Precapillary sphincters Arteriovenous bypass Figure 15 3b 3 of 4 When precapillary sphincters are relaxed blood flows through all capillaries in the bed Arteriole Precapillary sphincters relaxed Venule Capillaries Figure 15 3c 4 of 4 If precapillary sphincters constrict blood flow bypasses capillaries completely and flows through metarterioles Precapillary sphincters constricted Exchange Takes Place in the Capillaries and Postcapillary Venules Absence of vascular smooth muscle and elastic tissue reinforcement in capillaries and postcapillary venules facilitates exchange as does the large surface area In other words because capillaries have very thin walls and are very numerous diffusion distance from the capillary lumen to tissue cells is very short 2013 Pearson Education Inc Capillaries Exchange Plasma and cells exchange materials across thin capillary walls Capillary density is related to metabolic activity of cells in the tissue Capillaries have the thinnest walls Single layer of flattened endothelial cells Supported by basal lamina Bone marrow liver and spleen do not have typical capillaries but rather sinusoids 2013 Pearson Education Inc Figure 15 16a 1 of 2 Continuous capillaries have leaky junctions Heart brain skeletal muscle skin Nucleus Endothelial cells beneath basement membrane Transcytosis vesicular transport Endothelial cell junctions allow water and small dissolved solutes to pass Basement membrane Transcytosis vesicles Transcytosis brings proteins and macromolecules across endothelium Some vesicles may fuse to create temporary channels Figure 15 16b 2 of 2 Fenestrated capillaries have large pores GI tract kidneys Fenestrated pores Basement membrane cut Transcytosis vesicular transport Transcytosis vesicles Fenestrations or pores Transcytosis brings proteins and macromolecules across endothelium Some vesicles may fuse to create temporary channels Endothelial cell junction Basement membrane Capillary Exchange Exchange between plasma and interstitial fluid occurs by paracellular pathway or endothelial transport Small dissolved solutes and gases move by diffusion depending on lipid solubility and concentration gradient Larger solutes and proteins move mostly by vesicular transport and by bulk flow 2013 Pearson Education Inc Figure 15 17 35 28 Velocity of blood flow depends on the total cross sectional area 21 14 Total cross sectional area cm2 Veins Venules Capillaries Arterioles Arteries 0 5000 4000 3000 2000 1000 0 GRAPH QUESTION a Is velocity directly proportional to or inversely