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Heart stimulation



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Heart stimulation

  1. 1. Physiology of the Heart Dr. George Pearce
  2. 2. Functions of the Heart <ul><li>Generating blood pressure </li></ul><ul><li>Routing blood: separates pulmonary and systemic circulations </li></ul><ul><li>Ensuring one-way blood flow: valves </li></ul><ul><li>Regulating blood supply </li></ul><ul><ul><li>Changes in contraction rate and force match blood delivery to changing metabolic needs </li></ul></ul>
  3. 3. The cardiovascular system is divided into two circuits <ul><li>Pulmonary circuit </li></ul><ul><ul><li>blood to and from the lungs </li></ul></ul><ul><li>Systemic circuit </li></ul><ul><ul><li>blood to and from the rest of the body </li></ul></ul><ul><li>Vessels carry the blood through the circuits </li></ul><ul><ul><li>Arteries carry blood away from the heart </li></ul></ul><ul><ul><li>Veins carry blood to the heart </li></ul></ul><ul><ul><li>Capillaries permit exchange </li></ul></ul>
  4. 5. <ul><li>Structural Differences in heart chambers </li></ul><ul><ul><li>The left side of the heart is more muscular than the right side </li></ul></ul><ul><li>Functions of valves </li></ul><ul><ul><li>AV valves prevent backflow of blood from the ventricles to the atria </li></ul></ul><ul><ul><li>Semilunar valves prevent backflow into the ventricles from the pulmonary trunk and aorta </li></ul></ul>Heart chambers and valves
  5. 7. Cardiac Muscle Contraction <ul><li>Heart muscle: </li></ul><ul><ul><li>Is stimulated by nerves and is self-excitable </li></ul></ul><ul><ul><li>Cardiac muscle contraction is similar to skeletal muscle contraction </li></ul></ul>
  6. 8. Conducting System of Heart
  7. 9. Heart Physiology: Sequence of Excitation <ul><li>Sinoatrial (SA) node generates impulses about 75 times/minute </li></ul><ul><li>Atrioventricular (AV) node delays the impulse approximately 0.1 second </li></ul><ul><li>Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His) to the Purkinje fibers and finally to the myocardial fibers </li></ul>
  8. 10. Impulse Conduction through the Heart
  9. 11. An Electrocardiogram
  10. 12. ECGs, Normal and Abnormal
  11. 13. ECGs, Abnormal Arrhythmia: conduction failure at AV node No pumping action occurs
  12. 14. Factors Affecting Cardiac Output Figure 20.20
  13. 15. Heart Rate <ul><li>Pulse = surge of pressure in artery </li></ul><ul><ul><li>infants have HR of 120 bpm or more </li></ul></ul><ul><ul><li>young adult females avg. 72 - 80 bpm </li></ul></ul><ul><ul><li>young adult males avg. 64 to 72 bpm </li></ul></ul><ul><ul><li>HR rises again in the elderly </li></ul></ul>
  14. 16. Preload and Afterload Figure 18.21
  15. 17. Effects of Hormones on Contractility <ul><li>Epi, NE, and Thyroxine all have positive ionotropic effects and thus  contractility </li></ul><ul><li>Digitalis elevates intracellular Ca ++ concentrations by interfering with its removal from sarcoplasm of cardiac cells </li></ul><ul><li>Beta-blockers ( propanolol, timolol ) block beta-receptors and prevent sympathetic stimulation of heart (neg. chronotropic effect) </li></ul>
  16. 18. Exercise and Cardiac Output <ul><li>Proprioceptors </li></ul><ul><ul><li>HR  at beginning of exercise due to signals from joints, muscles </li></ul></ul><ul><li>Venous return </li></ul><ul><ul><li>muscular activity  venous return causes  SV </li></ul></ul><ul><li> HR and  SV cause  CO </li></ul><ul><li>Exercise produces ventricular hypertrophy </li></ul><ul><ul><li> SV allows heart to beat more slowly at rest </li></ul></ul><ul><ul><li> cardiac reserve </li></ul></ul>
  17. 19. Factors Involved in Regulation of Cardiac Output


  • Insert Process Fig. 20.13 with verbiage, Insert Animation: Conducting System of the Heart.exe
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