heart physiology

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  • 1. HeartPhysiology Department of PhysiologySKZMDC

2. 3. 4. Cardiac Muscle

  • Cardiac Muscle
      • Atrial muscle
      • Ventricular muscle
      • Specializedexcitatory & conductive muscle bers
  • Cardiac Muscle as aSyncytium
      • Intercalated disccommunicating junctions (gap junctions) - totally free diffusion of ions
      • Atrial syncytium
      • Ventricular syncytium

5. Cardiac Muscle -Histology 6. 7. 8. Cardiac Muscle Action Potential

  • Depolarization
      • Fast Na +channels
  • Plateau
      • Slow Ca ++channels
        • Slow to open
        • Slow to close
      • After depol. cardiac muscle membrane permeability to K +decreases
      • Ca ++thus pumped in excitation-contraction coupling
  • Repolarization
      • Slow K +channels
  • Refractory Periods
      • 0.25 - 0.3 sec (Absolute)
        • Corresponds to plateau
      • 0.05 sec (Relative)

9. AP Comparison 10. Cardiac Muscle Action Potential 11. Cardiac Muscle Action Potential 12. Problem

  • A drug is found to partially inactivate fast sodium channels.
  • Q: How would this drug alter the action potential in a ventricular myocyte?
  • Q: How would the drug alter conduction velocity within the ventricle?

13. Cardiac Cycle

  • Cardiac events occurring from beginning of one heartbeat to the beginning of the next beat
  • Each cycle INITIATEDby SA node
        • Spontaneous generation of AP inSA node
        • AP travels through both atria
        • Through A-V bundle into the ventricles
          • AV node delay (more than 0.1 second)
          • Hence atria contract ahead of ventricles
  • Diastole and Systole
        • Period of relaxation Diastole
          • Heart fills with blood
        • Period of contraction Systole
          • Ejection of blood

14. Cardiac Cycle - Components

  • ECG is the event marker
  • 1. Atrial Systole
        • FollowsPwave (electric activation of atria)
        • Contributes to ventricular filling
        • Forms the a wave in the venous pulse curve
        • Ventricular filling by atrial systole 4 thheart sound(not audible in normal adults)
  • 2. Isovolumetric contraction of Ventricle
        • Occurs after QRS wave (electric activation of ventricles)
        • Ventricular P raised above atrial P:
          • AV valves close ( 1 stheart sound )
          • Split in 1 stheart sound may occur (since mitral valve closes b/f tricuspid)
        • Ventricular P rises NO CHANGE IN VOLUME
          • Aortic valve is closed

15. Cardiac Cycle - Components

  • 3. Rapid Ventricular Ejection
        • Ventricular P reaches its max.
        • When it b/c greater than aortic P aortic valve opens
          • Rapid ejection of blood takes place
        • Ventricular volume decreases rapidly
        • Atrial filling begins
        • Onset of T wave (ventricular repolarization) marks end of vent. contraction & ejection
  • 4.Reduced Ventricular Ejection
        • Slower ejection of blood from ventricles
        • Ventricle P decreases
        • Aortic P decreases (runoff of blood from large arteries into smaller arteries)
        • Atrial filling continues

16. Cardiac Cycle - Components

  • 5. Isovolumetric Ventricular Relaxation
        • Ventricle replorization is complete (end of T wave)
        • Aortic valve closes (followed by pulmonic valve)
          • 2 ndheart sound
          • Splitting occurs during inspiration
        • AV valves remain closed mostly during this phase
        • Ventricle P drops rapidly
        • Ventricle volume remains CONSTANT all valves are closed
        • Incisura
        • When ventricle P b/c < atrial P mitral valve opens
  • 6. Rapid Ventricular Filling
        • Post-mitral valve opening rapid filling of ventricles occurs
        • Aortic P continues to decrease more run-off of blood
        • 3 rdheart sound(due to rapid flow from atria to ventricles
          • Normally heard in children
          • Abnormal in adults
  • 7. Reduced Ventricular Filling (Diastasis)
        • Longest phase of cardiac cycle
        • Ventricular filling slows down
        • Diastasis time period depends on heart rate!

17. 18. 19. Cardiac Cycle

  • End-diastolic volume (130 ml)
  • End-systolic volume (50 ml)
  • Stroke volume (70 to 90 ml - @ rest)
  • Ejection fraction
        • % of end-diastolic ventricular volume that is ejected with each stroke
        • Is about 65%
        • Valuable index of ventricular function
  • Preload
  • Afterload

20. Cardiac Chamber Pressures 21. Length (L) Tension (T) Curve Isolated Cardiac Muscle 22. Pressure (T) Volume (L) Curve Whole Heart

  • PV loops:
    • Depict cardiac cycle
    • Show effects of Preload, afterload & inotropic state on cardiac pumping ability (SV)

23. 24. Regulation of Heart Pumping

  • (1)INTRINSICcardiac regulation of pumping in response to changes in volume of blood owing into the heart ( Frank-Starling Law )
  • (2) Control of heart rate and strength of heart pumping by ANS

25. Frank-Starling Law

  • Volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole
  • Underlying principle