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Chapter 13

Chapter 13. Blood, Heart and Circulation. 13-1. 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

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Chapter 13

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  1. Chapter 13 Blood, Heart and Circulation 13-1

  2. Components of Circulatory System • Include cardiovascular and lymphaticsystems • 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

  3. 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

  4. Cardiac Cycle 13-42

  5. 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 0.1-0.2 sec later 13-43

  6. 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

  7. Cardiac Cycle continued • 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 isovolumetricrelaxation • When pressure in ventricles falls below atria, AVs open and ventricles fill • Atrial systole sends its blood into ventricles 13-45

  8. 13-46

  9. 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

  10. SA Node Pacemaker • In normal heart, SA node functions as pacemaker • Depolarizes spontaneously to threshold (= pacemaker potential) 13-53

  11. SA Node Pacemaker continued • 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 Ca2+ channels open, creating upstroke and contraction • Repolarization is via opening of V-gated K+ channels 13-54

  12. 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

  13. Conduction of APs • APs from SA node spread at rate of 0.8 -1 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

  14. 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

  15. 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

  16. 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

  17. Capillaries • Provide extensive surface area for exchange • Blood flow through a capillary bed is determined by state of precapillary sphincters of arteriole supplying it 13-74

  18. Types of Capillaries • 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 13-75

  19. Veins • Contain majority of blood in circulatory system • Very compliant (expand readily) • Contain very low pressure (about 2mm Hg) • Insufficient to return blood to heart 13-76

  20. Veins • 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 13-77

  21. Heart Disease 13-78

  22. 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

  23. Atherosclerosis • Plaques begin at sites of damage to endothelium • E.g. from hypertension, smoking, high cholesterol, or diabetes 13-80

  24. Atherosclerosis • Plaques begin at sites of damage to endothelium • E.g. from hypertension, smoking, high cholesterol, or diabetes 13-81

  25. 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

  26. 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

  27. Lymphatic System 13-93

  28. 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

  29. Lymphatic System continued • Lymphatic capillaries are closed-end tubes that form vast networks in intercellular spaces • Very porous, absorb proteins, microorganisms, fat 13-95

  30. Lymphatic System continued • Lymph is carried from lymph capillaries to lymph ducts to lymph nodes 13-96

  31. Lymphatic System continued • 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 13-97

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