Lecture Notes on Heart Function and Cardiac Physiology

Overview of Heart Function

• The heart functions as a pump to circulate blood throughout the body.
• Four Chambers of the Heart:
  • Right Atrium
  • Right Ventricle
  • Left Atrium
  • Left Ventricle
• The ventricles pump blood out of the heart and are composed of cardiac muscle cells.

Circulation of Blood

• Deoxygenated Blood:
  • Travels from body tissues to the heart via the vena cava.
  • Enters the right atrium, then the right ventricle.
  • Pumped to lungs via pulmonary artery for reoxygenation.
• Oxygenated Blood:
  • Returns to the heart from the lungs through the pulmonary vein.
  • Enters left atrium, then left ventricle.
  • Pumped to the rest of the body through the aorta.
• Types of Circulation:
  • Pulmonary Circulation: between heart and lungs.
  • Systemic Circulation: between heart and body tissues.

Cardiac Muscle Cells

• Differ from skeletal and smooth muscles but share some features:
  • Striated and usually mono-nucleated.
  • Contain intercalated discs for unified contraction.
• Use t-tubules and sarcoplasmic reticulum for calcium release.

Action Potentials in Cardiac Muscle Cells

• Membrane Potential:
  • Difference in electrical potential across a cell membrane.
  • At rest, inside of cell is negative relative to outside.
• Ions Involved:
  • Calcium, Sodium (outside)
  • Potassium (inside)
• Ion Channels:
  • Movement of ions through channels alters membrane potential.

Membrane Potential Process

• Depolarization:
  • Sodium influx makes membrane potential positive (~+30 mV).
• Plateau Phase:
  • Calcium influx through L-type channels maintains positively charged potential.
• Repolarization:
  • Calcium channels close; Potassium efflux returns potential to negative (~-90 mV).

Absolute Refractory Period

• Period when a second action potential cannot be generated.
• Ensures contraction and action potential processes do not overlap.

Pacemaker Cells

• Sinoatrial Node (SA Node):
  • Main pacemaker, generates action potentials, controls heart rate (70-80 bpm).
• Atrioventricular Node (AV Node):
  • Backup pacemaker, slower rate (40-60 bpm).
• Bundle of His and Purkinje Fibers:
  • Can generate low-frequency action potentials (20-40 bpm).

Pacemaker Cell Activity

• Self-generated action potentials without neuron assistance.
• Phases:
  • Pacemaker potential (slow calcium influx).
  • Depolarization (rapid calcium influx).
  • Repolarization (potassium efflux).

Conclusion

• Understanding the cardiac cycle and blood supply (coronary arteries) will be covered next.

• Study Tip: Review the structure of the heart and pathways of blood circulation for a better grasp of the cardiac cycle.
• Next Steps: Further explore coronary circulation and cardiac cycle dynamics.

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