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  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 17 Heart Purkinje fibers
  2. 2. Functions of the Heart <ul><li>Generating blood pressure </li></ul><ul><ul><li>Required for blood flow through the blood vessels </li></ul></ul><ul><li>Routing blood </li></ul><ul><ul><li>Two pumps, moving blood through the pulmonary and systemic circulations </li></ul></ul><ul><li>Regulating blood supply </li></ul><ul><ul><li>Adjusts blood flow by changing the rate and force of heart contractions as needed </li></ul></ul>
  3. 3. Systemic and Pulmonary Circulation <ul><li>Pulmonary circulation </li></ul><ul><ul><li>The flow of blood from the heart through the lungs back to the heart </li></ul></ul><ul><ul><li>Picks up oxygen and releases carbon dioxide in the lungs </li></ul></ul><ul><li>System circulation </li></ul><ul><ul><li>The flow of blood from the heart through the body back to the heart </li></ul></ul><ul><ul><li>Delivers oxygen and picks up carbon dioxide in the body’s tissues </li></ul></ul>Fig. 17.1
  4. 4. Location, Shape, and Size of the Heart <ul><li>Location </li></ul><ul><ul><li>Anterior to the vertebral column, posterior to the sternum </li></ul></ul><ul><ul><li>Left of the midline </li></ul></ul><ul><ul><li>Deep to the second to fifth intercostal spaces </li></ul></ul><ul><ul><li>Superior surface of diaphragm </li></ul></ul><ul><li>Shaped like a blunt cone, with an apex and a base </li></ul><ul><li>Approximately the size of your fist </li></ul>
  5. 5. Fig. 17.2
  6. 6. Anatomy of the Heart <ul><li>The heart consists of two atria and two ventricles </li></ul><ul><li>Pericardium: a double-walled sac around the heart composed of </li></ul><ul><ul><li>A superficial fibrous pericardium </li></ul></ul><ul><ul><li>A deep two-layer serous pericardium </li></ul></ul><ul><ul><ul><li>The parietal layer lines the internal surface of the fibrous pericardium </li></ul></ul></ul><ul><ul><ul><li>The visceral layer lines the surface of the heart </li></ul></ul></ul><ul><ul><ul><li>They are separated by the fluid-filled (pericardial fluid) pericardial cavity </li></ul></ul></ul>
  7. 7. Anatomy of the Heart <ul><li>The pericardium </li></ul><ul><ul><li>Fibrous pericardium </li></ul></ul><ul><ul><ul><li>Protects and anchors the heart </li></ul></ul></ul><ul><ul><ul><li>Prevents overfilling of the heart with blood </li></ul></ul></ul><ul><ul><li>Serous pericardium </li></ul></ul><ul><ul><ul><li>Allows for the heart to work in a relatively friction-free environment </li></ul></ul></ul>
  8. 8. Heart in the Pericardium Fig. 17.3
  9. 9. Anatomy of the Heart <ul><li>The heart wall has three layers </li></ul><ul><ul><li>Epicardium </li></ul></ul><ul><ul><ul><li>Visceral layer of the serous pericardium (visceral pericardium) </li></ul></ul></ul><ul><ul><ul><li>Provides protection against the friction of rubbing organs </li></ul></ul></ul><ul><ul><li>Myocardium </li></ul></ul><ul><ul><ul><li>Cardiac muscle layer forming the bulk of the heart </li></ul></ul></ul><ul><ul><ul><li>Responsible for contraction </li></ul></ul></ul><ul><ul><li>Endocardium </li></ul></ul><ul><ul><ul><li>Endothelial layer over crisscrossing, interlacing layer of connective tissue </li></ul></ul></ul><ul><ul><ul><li>Inner endocardium reduces the friction resulting from the passage of blood through the heart </li></ul></ul></ul><ul><li>Ventricles have ridges called trabeculae carneae </li></ul><ul><li>The inner surfaces of the atria are mainly smooth </li></ul><ul><ul><li>Auricles have raised areas called musculi pectinati </li></ul></ul>
  10. 10. Heart Wall Fig. 17.4
  11. 11. Anatomy of the Heart <ul><li>Atria </li></ul><ul><ul><li>Receiving chambers of the heart </li></ul></ul><ul><ul><li>Each atrium has a protruding auricle </li></ul></ul><ul><ul><li>Pectinate muscles mark atrial walls </li></ul></ul><ul><ul><li>Veins entering the right atrium carry blood to the heart from the systemic circulation </li></ul></ul><ul><ul><ul><li>Inferior vena cava </li></ul></ul></ul><ul><ul><ul><li>Superior vena cava </li></ul></ul></ul><ul><ul><ul><li>Coronary sinus </li></ul></ul></ul><ul><ul><li>Veins entering the left atrium carry blood to the heart from the pulmonary circulation </li></ul></ul><ul><ul><ul><li>Four pulmonary veins </li></ul></ul></ul>
  12. 12. Anatomy of the Heart <ul><li>Ventricles </li></ul><ul><ul><li>Discharging chambers of the heart </li></ul></ul><ul><ul><li>Papillary muscles and trabeculae carneae muscles mark ventricular walls </li></ul></ul><ul><ul><li>Arteries carrying blood away from the heart </li></ul></ul><ul><ul><ul><li>Pulmonary trunk exits the right ventricle carrying blood to the pulmonary circulation </li></ul></ul></ul><ul><ul><ul><li>Aorta exits the left ventricle carrying blood to the systemic circulation </li></ul></ul></ul>
  13. 13. Anatomy of the Heart <ul><li>External Anatomy </li></ul><ul><ul><li>Each atrium has a flap called an auricle </li></ul></ul><ul><ul><li>The coronary sulcus separates the atria from the ventricles </li></ul></ul><ul><ul><li>The interventricular grooves separate the right and left ventricles </li></ul></ul><ul><li>Heart Chambers </li></ul><ul><ul><li>The interatrial septum separates the atria from each other </li></ul></ul><ul><ul><li>The fossa ovalis is the former location of the foramen ovalis through which blood bypassed the lungs in the fetus </li></ul></ul><ul><ul><li>The interventricular septum separates the ventricles </li></ul></ul>
  14. 14. Fig. 17.5ab Surface View of the Heart
  15. 15. Surface View of the Heart Fig. 17.5c
  16. 16. Anatomy of the Heart <ul><li>Heart valves </li></ul><ul><ul><li>Ensure unidirectional blood flow through the heart </li></ul></ul><ul><ul><li>Atrioventricular (AV) valves lie between the atria and the ventricles </li></ul></ul><ul><ul><li>AV valves prevent backflow into the atria when ventricles contract </li></ul></ul><ul><ul><li>Chordae tendineae anchor AV valves to papillary muscles </li></ul></ul><ul><ul><li>Tricuspid valve: separates the right atrium and ventricle </li></ul></ul><ul><ul><li>Bicuspid valve: separates the left atrium and ventricle </li></ul></ul>
  17. 17. Anatomy of the Heart <ul><li>Heart valves (cont.) </li></ul><ul><ul><li>Semilunar valves prevent backflow of blood into the ventricles </li></ul></ul><ul><ul><li>Aortic semilunar valve: lies between the left ventricle and the aorta </li></ul></ul><ul><ul><li>Pulmonary semilunar valve: lies between the right ventricle and pulmonary trunk </li></ul></ul>
  18. 18. Internal Anatomy of the Heart Fig. 17.6
  19. 19. Heart Valves Fig. 17.7
  20. 20. Function of the Heart Valves Fig. 17.8
  21. 21. Route of Blood Flow Through the Heart <ul><li>Blood from the body flows through the right atrium into the right ventricle and then to the lungs </li></ul><ul><li>Blood returns from the lungs to the left atrium, enters the left ventricle, and is pumped back to the body </li></ul>
  22. 22. Fig. 17.9 Blood Flow Through the Heart
  23. 23. Blood Supply to the Heart <ul><li>Coronary arteries branch off the aorta to supply the heart </li></ul><ul><li>Blood returns from the heart tissues to the right atrium through coronary sinus and cardiac veins </li></ul>Fig. 17.10
  24. 24. Page 497
  25. 25. Histology of the Heart <ul><li>Fibrous Skeleton of the Heart </li></ul><ul><ul><li>Consists of a plate of fibrous connective tissue </li></ul></ul><ul><ul><li>Forms fibrous rings around the AV and SL valves for support </li></ul></ul><ul><ul><li>Provides a point of attachment for heart muscle </li></ul></ul><ul><ul><li>Electrically insulates the atria from the ventricles </li></ul></ul>
  26. 26. Histology of the Heart <ul><li>Cardiac Muscle Cells </li></ul><ul><ul><li>Are branched and have a centrally located nucleus </li></ul></ul><ul><ul><li>Actin and myosin are organized to form sarcomeres (striated) </li></ul></ul><ul><ul><li>T tubules and sarcoplasmic reticulum are not as organized as in skeletal muscle </li></ul></ul><ul><ul><li>Normal contraction depends on extracellular Ca 2+ </li></ul></ul><ul><ul><li>Rely on aerobic respiration for ATP production </li></ul></ul><ul><ul><ul><li>They have many mitochondria and are well supplied with blood vessels </li></ul></ul></ul><ul><ul><li>Joined by intercalated disks </li></ul></ul><ul><ul><ul><li>Allow action potentials to move from one cell to the next, thus cardiac muscle cells function as a unit </li></ul></ul></ul>
  27. 27. Histology of the Heart Fig. 17.11
  28. 29. Electrical Activity of the Heart <ul><li>Action Potentials </li></ul><ul><ul><li>After depolarization and partial repolarization, a plateau phase is reached, during which the membrane potential only slowly repolarizes </li></ul></ul><ul><ul><li>The opening and closing of voltage-gated ion channels produce the action potential </li></ul></ul><ul><ul><ul><li>The movement of Na + through Na + channels causes depolarization </li></ul></ul></ul><ul><ul><ul><li>During depolarization, K + channels close and Ca 2+ channels begin to open </li></ul></ul></ul><ul><ul><ul><li>Early repolarization results from closure of the Na + channels and the opening of some K + channels </li></ul></ul></ul><ul><ul><ul><li>The plateau exists because Ca 2+ channels remain open </li></ul></ul></ul><ul><ul><ul><li>The rapid phase of repolarization results from the closure of the Ca 2+ channels and the opening of many K + channels </li></ul></ul></ul>
  29. 30. Electrical Activity of the Heart <ul><li>Refractory Periods </li></ul><ul><ul><li>Absolute refractory period </li></ul></ul><ul><ul><ul><li>Cardiac muscle cells are insensitive to further stimulation </li></ul></ul></ul><ul><ul><li>Relative refractory period </li></ul></ul><ul><ul><ul><li>Stronger than normal stimulation can produce an action potential </li></ul></ul></ul><ul><ul><li>Cardiac muscle has a prolonged depolarization and thus a prolonged absolute refractory period, which allows time for the cardiac muscle to relax before the next action potential causes a contraction </li></ul></ul>
  30. 31. Fig. 17.12
  31. 33. Electrical Activity of the Heart <ul><li>Autorhythmicity of Cardiac Muscle </li></ul><ul><ul><li>Some cardiac muscle cells are autorhythmic because of the spontaneous development of a prepotential </li></ul></ul><ul><ul><ul><li>Prepotential: slowly developing local action potential </li></ul></ul></ul><ul><ul><li>The sinoatrial (SA) node is the pacemaker of the heart </li></ul></ul><ul><ul><ul><li>Collection of cardiac muscle cells capable of spontaneously generating action potentials </li></ul></ul></ul><ul><ul><li>The prepotential results from the movement of Na+ and Ca 2+ into the SA node cells </li></ul></ul><ul><ul><li>The duration of the prepotential determines heart rate </li></ul></ul>
  32. 34. Electrical Activity of the Heart <ul><li>Conducting System of the Heart </li></ul><ul><ul><li>The sinoatrial (SA) node and the atrioventricular (AV) node are in the right atrium </li></ul></ul><ul><ul><li>The AV node is connected to the bundle branches in the interventricular septum by the AV bundle </li></ul></ul><ul><ul><li>The bundle branches give rise to Purkinje fibers , which supply the ventricles </li></ul></ul>
  33. 35. Electrical Activity of the Heart <ul><li>Conducting System of the Heart </li></ul><ul><ul><li>The SA node initiates action potentials, which spread across the atria and cause them to contract </li></ul></ul><ul><ul><ul><li>SA node generates impulses about 75 times/minute </li></ul></ul></ul><ul><ul><li>Action potentials are slowed in the AV node, allowing the atria to contract and blood to move into the ventricles </li></ul></ul><ul><ul><ul><li>AV node delays the impulse approximately 0.11 seconds </li></ul></ul></ul><ul><ul><li>Then the action potentials passes from atria to ventricles via the atrioventricular bundle </li></ul></ul>
  34. 37. Electrical Activity of the Heart <ul><li>Conducting System of the Heart </li></ul><ul><ul><li>AV bundle splits into two pathways in the interventricular septum (bundle branches) </li></ul></ul><ul><ul><li>Bundle branches carry the impulse toward the apex of the heart </li></ul></ul><ul><ul><li>Purkinje fibers carry the impulse to the heart apex and ventricular walls </li></ul></ul>
  35. 38. Fig. 17.13
  36. 40. Electrical Activity of the Heart <ul><li>Electrocardiogram (ECG) </li></ul><ul><ul><li>Records only the electrical activities of the heart </li></ul></ul><ul><ul><li>P wave corresponds to depolarization of the atria (SA node) </li></ul></ul><ul><ul><li>QRS complex corresponds to ventricular depolarization </li></ul></ul><ul><ul><li>T wave corresponds to ventricular repolarization </li></ul></ul><ul><ul><li>Atrial repolarization record is masked by the larger QRS complex </li></ul></ul><ul><li>Based on the magnitude of the ECG waves and the time between waves, ECGs can be used to diagnose heart abnormalities </li></ul>
  37. 41. Fig. 17.14
  38. 42. Cardiac Cycle <ul><li>Repetitive contraction and relaxation of the heart chambers </li></ul><ul><li>Overview of Systole and Diastole </li></ul><ul><ul><ul><li>Atrial systole is contraction of the atria </li></ul></ul></ul><ul><ul><ul><li>Systole is contraction of the ventricles </li></ul></ul></ul><ul><ul><ul><li>Atrial diastole is relaxation of the atria </li></ul></ul></ul><ul><ul><ul><li>Diastole is relaxation of the ventricles </li></ul></ul></ul>
  39. 43. Cardiac Cycle <ul><li>Overview of Systole and Diastole (cont.) </li></ul><ul><ul><li>During systole </li></ul></ul><ul><ul><ul><li>AV valves close </li></ul></ul></ul><ul><ul><ul><li>Pressure increases in the ventricles </li></ul></ul></ul><ul><ul><ul><li>Semilunar valves are forced to open </li></ul></ul></ul><ul><ul><ul><li>Blood flows into the aorta and pulmonary trunk </li></ul></ul></ul><ul><ul><li>At the beginning of diastole </li></ul></ul><ul><ul><ul><li>Pressure in the ventricles decreases </li></ul></ul></ul><ul><ul><ul><li>Semilunar valves close to prevent backflow of blood from the aorta and pulmonary trunk into the ventricles </li></ul></ul></ul><ul><ul><li>When the pressure in the ventricles is lower than in the atria, the AV valves open and blood flows from the atria into the ventricles </li></ul></ul><ul><ul><li>During atrial systole, the atria contract and complete the filling of the ventricles </li></ul></ul>
  40. 44. Fig. 17.15 Cardiac Cycle
  41. 45. Cardiac Cycle <ul><li>Events Occurring During Ventricular Systole </li></ul><ul><ul><li>Ventricular depolarization </li></ul></ul><ul><ul><ul><li>Produces the QRS complex </li></ul></ul></ul><ul><ul><ul><li>Initiates contraction of the ventricles, which increases ventricular pressure </li></ul></ul></ul><ul><ul><ul><ul><li>The AV valves close </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Semilunar valves open </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Blood is ejected from the heart </li></ul></ul></ul></ul><ul><ul><li>The volume of blood in a ventricle just before it contracts is the end- diastolic volume </li></ul></ul><ul><ul><li>The volume of blood after contraction is the end- systolic volume </li></ul></ul>
  42. 46. Cardiac Cycle <ul><li>Events Occurring During Ventricular Diastole </li></ul><ul><ul><li>Ventricular repolarization </li></ul></ul><ul><ul><ul><li>Produces the T wave </li></ul></ul></ul><ul><ul><ul><li>Ventricles relax </li></ul></ul></ul><ul><ul><ul><ul><li>Blood flowing back toward the relaxed ventricles closes the semilunar valves </li></ul></ul></ul></ul><ul><ul><ul><ul><li>The AV valves open and blood flows into the ventricles </li></ul></ul></ul></ul><ul><ul><ul><li>Approximately 70% of ventricular filling occurs when blood flows from the higher pressure in the veins and atria to the lower pressure in the relaxed ventricles </li></ul></ul></ul><ul><ul><ul><li>Atrial depolarization produces the P wave </li></ul></ul></ul><ul><ul><ul><li>The atria contract and complete ventricular filling </li></ul></ul></ul>
  43. 47. Cardiac Cycle <ul><li>Aortic Pressure Curve </li></ul><ul><ul><li>Contraction of the ventricles forces blood into the aorta </li></ul></ul><ul><ul><ul><li>The maximum pressure in the aorta is the systolic pressure </li></ul></ul></ul><ul><ul><li>Elastic recoil of the aorta maintains pressure in the aorta and produces the dicrotic notch </li></ul></ul><ul><ul><li>Blood pressure in the aorta falls as blood flows out of the aorta </li></ul></ul><ul><ul><ul><li>The minimum pressure in the aorta is the diastolic pressure </li></ul></ul></ul>
  44. 48. Cardiac Cycle <ul><li>Heart sounds (lub-dup) are associated with closing of heart valves </li></ul><ul><ul><li>First sound occurs as AV valves close and signifies beginning of systole </li></ul></ul><ul><ul><li>Second sound occurs when SL valves close at the beginning of ventricular diastole </li></ul></ul>
  45. 49. Fig. 17.17
  46. 50. Fig. 17.16 Events Occurring During the Cardiac Cycle
  47. 51. Tab. 17.2
  48. 52. Tab. 17.1
  49. 54. Mean Arterial Blood Pressure <ul><li>Mean arterial pressure is the average blood pressure in the aorta </li></ul><ul><ul><li>Adequate blood pressure is necessary to ensure delivery of blood to the tissues </li></ul></ul><ul><ul><li>Proportional to cardiac output (amount of blood pumped by the heart per minute) times peripheral resistance (total resistance to blood flow through blood vessels) </li></ul></ul><ul><ul><li>CO X PR </li></ul></ul>
  50. 55. Mean Arterial Blood Pressure <ul><li>CO is the product of heart rate (HR) and stroke volume (SV) </li></ul><ul><ul><li>HR is the number of heart beats per minute </li></ul></ul><ul><ul><li>SV is the amount of blood pumped out by a ventricle with each beat </li></ul></ul><ul><ul><ul><li>SV = end-diastolic volume (EDV) minus end-systolic volume (ESV) </li></ul></ul></ul><ul><ul><ul><ul><li>EDV = amount of blood collected in a ventricle during diastole </li></ul></ul></ul></ul><ul><ul><ul><ul><li>ESV = amount of blood remaining in a ventricle after contraction </li></ul></ul></ul></ul><ul><ul><li>CO (ml/min) = HR (72 beats/min) x SV (70 ml/beat) </li></ul></ul><ul><ul><li>CO = 5040 ml/min (~5 L/min) </li></ul></ul><ul><li>Cardiac reserve is the difference between resting and maximal CO </li></ul>
  51. 56. Mean Arterial Blood Pressure <ul><li>Venous return is the amount of blood returning to the heart </li></ul><ul><ul><li>Increased venous return increases stroke volume by increasing end-diastolic volume </li></ul></ul><ul><li>Increased force of contraction increases stroke volume by decreasing end-systolic volume </li></ul>
  52. 57. Regulation of the Heart <ul><li>Intrinsic Regulation </li></ul><ul><ul><li>Modifies stroke volume through the functional characteristics of cardiac muscle cells </li></ul></ul><ul><ul><li>Starling’s law of the heart describes the relationship between preload and the stroke volume of the heart </li></ul></ul><ul><ul><ul><li>An increased preload causes the cardiac muscle fibers to contract with a greater force and produce a greater stroke volume </li></ul></ul></ul><ul><ul><li>Afterload is the pressure against which the ventricles must pump blood. </li></ul></ul>
  53. 58. Regulation of the Heart <ul><li>Extrinsic Regulation </li></ul><ul><ul><li>Modifies heart rate and stroke volume through nervous and hormonal mechanisms </li></ul></ul><ul><ul><ul><li>The cardioregulatory center in the medulla oblongata regulates the parasympathetic and sympathetic nervous control of the heart </li></ul></ul></ul><ul><ul><ul><li>Epinephrine and norepinephrine are released into the blood from the adrenal medulla as a result of sympathetic stimulation. They increase the rate and force of heart contraction </li></ul></ul></ul>
  54. 59. Regulation of the Heart <ul><li>Parasympathetic stimulation is supplied by the vagus nerve </li></ul><ul><ul><li>Decreases heart rate. </li></ul></ul><ul><ul><li>Postganglionic neurons secrete acetylcholine, which increases membrane permeability to K. Hyperpolarization of the plasma membrane increases the duration of the prepotential </li></ul></ul><ul><li>Sympathetic stimulation is supplied by the cardiac nerves </li></ul><ul><ul><li>Increases heart rate and the force of contraction (stroke volume) </li></ul></ul><ul><ul><li>Postganglionic neurons secrete norepinephrine, which increases membrane permeability to Ca2+. Depolarization of the plasma membrane decreases the duration of the prepotential </li></ul></ul>
  55. 60. The Heart and Homeostasis <ul><li>Effect of Blood Pressure </li></ul><ul><ul><li>Baroreceptors monitor blood pressure and the cardioregulatory center modifies heart rate and stroke volume </li></ul></ul><ul><ul><li>In response to a decrease in blood pressure, the baroreceptor reflexes increase heart rate and stroke volume </li></ul></ul><ul><ul><li>When blood pressure increases, the baroreceptor reflexes decrease heart rate and stroke volume </li></ul></ul>
  56. 63. The Heart and Homeostasis <ul><li>Effect of pH, Carbon Dioxide, and Oxygen </li></ul><ul><ul><li>Carotid body and aortic chemoreceptor receptors monitor blood oxygen levels </li></ul></ul><ul><ul><li>Medullary chemoreceptors monitor blood pH and carbon dioxide levels </li></ul></ul><ul><ul><li>Chemoreceptors are not important for the normal regulation of the heart, but are important in the regulation of respiration and blood vessel constriction </li></ul></ul>
  57. 64. Baroreceptor and Chemoreceptor Reflexes Fig. 17.18
  58. 65. Fig. 17.19
  59. 66. The Heart and Homeostasis <ul><li>Effect of Ions and Body Temperature </li></ul><ul><ul><li>Increased extracellular K+ decrease heart rate and stroke volume </li></ul></ul><ul><ul><li>Decreased extracellular K+ decrease heart rate </li></ul></ul><ul><ul><li>Increased extracellular Ca2+ increase stroke volume and decrease heap rate </li></ul></ul><ul><ul><li>Decreased extracellular Ca2+ levels produce the opposite effect </li></ul></ul><ul><ul><li>Heart rate increases when body temperature increases, and it decreases when body temperature decreases </li></ul></ul>
  60. 67. Effects of Aging on the Heart <ul><li>Aging results in gradual changes in the function of the heart, which are minor under resting conditions but are more significant during exercise </li></ul><ul><li>Some age-related changes to the heart are the following </li></ul><ul><ul><li>Decreased cardiac output and heart rate </li></ul></ul><ul><ul><li>Increased cardiac arrhythmias </li></ul></ul><ul><ul><li>Hypertrophy of the left ventricle </li></ul></ul><ul><ul><li>Development of stenoses or incompetent valves </li></ul></ul><ul><ul><li>Development of coronary artery disease and heart failure </li></ul></ul><ul><li>Exercise improves the functional capacity of the heart at all ages. </li></ul>