Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 13 Blood, Heart and Circulation 13-1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Components of Circulatory System  Include cardiovascular and lymphatic systems  Heart pumps blood thru cardiovascular system  Blood vessels carry blood from heart to cells and back  Includes arteries, arterioles, capillaries, venules, veins  Lymphatic system picks up excess fluid filtered out in capillary beds and returns it to veins  Its lymph nodes are part of immune system 13-5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of Heart  Heart has 4 chambers  2 atria receive blood from venous system  2 ventricles pump blood to arteries  2 sides of heart are 2 pumps separated by muscular septum 13-32

Cardiac Cycle 13-42

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cardiac Cycle  Is repeating pattern of contraction and relaxation of heart  Systole refers to contraction phase  Diastole refers to relaxation phase  Both atria contract simultaneously; ventricles follow sec later 13-43

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cardiac Cycle  End-diastolic volume is volume of blood in ventricles at end of diastole  Stroke volume is amount of blood ejected from ventricles during systole  End-systolic volume is amount of blood left in ventricles at end of systole 13-44

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  As ventricles contract, pressure rises, closing AV valves  Called isovolumetric contraction because all valves are closed  When pressure in ventricles exceeds that in aorta, semilunar valves open and ejection begins  As pressure in ventricle falls below that in aorta, back pressure closes semilunars  All valves are closed and ventricles undergo isovolumetric relaxation  When pressure in ventricles falls below atria, AVs open and ventricles fill  Atrial systole sends its blood into ventricles Cardiac Cycle continued 13-45

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electrical Activity of Heart  Myocardial cells are short, branched, and interconnected by gap junctions  Entire muscle that forms a chamber is called a myocardium or functional syncytium  Because APs originating in any cell are transmitted to all others  Chambers separated by nonconductive tissue 13-52

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SA Node Pacemaker  In normal heart, SA node functions as pacemaker  Depolarizes spontaneously to threshold (= pacemaker potential) 13-53

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Membrane voltage begins at - 60mV and gradually depolarizes to -40 threshold  Spontaneous depolarization is caused by Na + flowing through channel that opens when hyperpolarized (HCN channel)  At threshold V-gated Ca 2+ channels open, creating upstroke and contraction  Repolarization is via opening of V-gated K + channels SA Node Pacemaker continued 13-54

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conducting Tissues of Heart continued  In septum of ventricles, His divides into right and left bundle branches  Which give rise to Purkinje fibers in walls of ventricles  These stimulate contraction of ventricles 13-59

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conduction of APs  APs from SA node spread at rate of m/sec  Time delay occurs as APs pass through AV node  Has slow conduction of 0.03– 0.05 m/sec  AP speed increases in Purkinje fibers to 5 m/sec  Ventricular contraction begins 0.1–0.2 sec after contraction of atria 13-60

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Refractory Periods  Heart contracts as syncytium and thus cannot sustain force  Its AP lasts about 250 msec  Has a refractory period almost as long as AP  Cannot be stimulated to contract again until has relaxed 13-62

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arteries  Large arteries are muscular and elastic  Contain lots of elastin  Thicker compared to veins  Part of autonomic nervous system  Expand during systole and recoil during diastole  Helps maintain smooth blood flow during diastole 13-72

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arteries  Small arteries and arterioles are muscular  Provide most resistance in circulatory system  Arterioles cause greatest pressure drop  Mostly connect to capillary beds  Some connect directly to veins to form arteriovenous anastomoses 13-73

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Provide extensive surface area for exchange  Blood flow through a capillary bed is determined by state of precapillary sphincters of arteriole supplying it Capillaries 13-74

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  In continuous capillaries, endothelial cells are tightly joined together  Have narrow intercellular channels that permit exchange of molecules smaller than proteins  Present in muscle, lungs, adipose tissue  Fenestrated capillaries have wide intercellular pores  Very permeable  Present in kidneys, endocrine glands, intestines.  Discontinuous capillaries have large gaps in endothelium  Are large and leaky  Present in liver, spleen, bone marrow Types of Capillaries 13-75

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Contain majority of blood in circulatory system  Very compliant (expand readily)  Contain very low pressure (about 2mm Hg)  Insufficient to return blood to heart Veins 13-76

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pump)  And pressure drops in chest during breathing  1-way venous valves ensure blood moves only toward heart Veins 13-77

Heart Disease 13-78

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atherosclerosis  Is most common form of arteriosclerosis (hardening of arteries)  Accounts for 50% of deaths in US  Localized plaques (atheromas) reduce flow in an artery  And act as sites for thrombus (blood clots) 13-79

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atherosclerosis  Plaques begin at sites of damage to endothelium  E.g. from hypertension, smoking, high cholesterol, or diabetes 13-80

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atherosclerosis  Plaques begin at sites of damage to endothelium  E.g. from hypertension, smoking, high cholesterol, or diabetes 13-81

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cholesterol and Plasma Lipoproteins  High blood cholesterol is associated with risk of atherosclerosis  Lipids, including cholesterol, are carried in blood attached to LDLs (low-density lipoproteins) and HDLs (high-density lipoproteins) 13-82

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cholesterol and Plasma Lipoproteins  LDLs and HDLs are produced in liver and taken into cells by receptor-mediated endocytosis  In cells LDL is oxidized  Oxidized LDL can injure endothelial cells facilitating plaque formation  Arteries have receptors for LDL but not HDL  Which is why HDL isn't atherosclerotic 13-83

Lymphatic System 13-93

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lymphatic System  Has 3 basic functions:  Transports interstitial fluid (lymph) back to blood  Transports absorbed fat from small intestine to blood  Helps provide immunological defenses against pathogens 13-94

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lymphatic System continued  Lymphatic capillaries are closed-end tubes that form vast networks in intercellular spaces  Very porous, absorb proteins, microorganisms, fat 13-95

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lymphatic System continued  Lymph is carried from lymph capillaries to lymph ducts to lymph nodes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Lymph nodes filter lymph before returning it to veins via thoracic duct or right lymphatic duct  Nodes make lymphocytes and contain phagocytic cells that remove pathogens  Lymphocytes also made in tonsils, spleen, thymus Lymphatic System continued 13-97