Cardiac Physiology Part I

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Cardiac Physiology Part I

• Frank A. Acevedo, PA-C

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Cardiac Tissues

• Atrial muscle
• Ventricular muscle
• Excitatory/conduction muscle fibers
• syncytium

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Cardiac Muscle Histology

• Uninucleate
• Branched
• Gap junctions

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Action Potential
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2
3
0
4
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Action Potential Continued

• Phase 4 - diastolic resting potential
• Phase 0 - depolarization of the cell
• Phases 1, 2, 3, - repolarization (primarily
  during Phase 3)

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Action Potential Continued

• Phase 0 is characterized by a rapid influx of
  sodium
• Phase 1 represents the overshoot and represents
  rapid termination of Na influx and increasing Ca
• Phase 2 is prolonged due to rapid inward movement
  of Ca and decreased leakage of K

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Action Potential Continued

• Ca movement during Phase 2 is very important for
  the excitation-contraction process
• Phase 3 is rapid repolarization due to rapid loss
  of K and stoppage of Na and Ca
• Phase 4 pacemaker potential

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Conduction Pathways
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Fundamental Features of Cardiac Excitation

• Automaticity
• capacity for self excitation
• Excitability
• ability to respond to stimuli and conduct action
  potentials
• Refractory Period
• time following excitation when another action
  potential can not be elicited and conducted
• Membrane Responsiveness
• relationship between membrane activation voltage
  and maximal rise of the AP

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Refractory Period
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Frank-Starling Effect

• Preload - availability of cross bridges
• An increase in the force of contraction is
  brought about by an increase in preload, up to a
  certain point
• rubber-band stretch

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