Understanding the Cardiac Cycle

Sep 10, 2024

Cardiac Cycle Lecture Notes

Introduction

  • Presenter: Leslie Samuel from Interactive Biology
  • Objective: Simplify the cardiac cycle and improve understanding.
  • Importance: Understanding the heart's function from the beginning of one heartbeat to the next.

Basics of Cardiac Cycle

  • Cardiac Cycle: Sequence of events in a heartbeat.
  • Blood Flow:
    • Blood enters through the atria:
      • Left side: Blood from lungs.
      • Right side: Blood from the rest of the body.
    • Atria contract → Blood pushed into ventricles.
    • Ventricles contract → Blood pushed out of the heart.
  • Concepts:
    • Systole: Contraction phase.

The ECG and Heart Function

  • Electrocardiogram (ECG): Shows electrical signals of the heart.
    • P Wave:
      • Represents atrial depolarization.
      • Causes atrial contraction (Atrial systole).
      • Increase in atrial pressure detected.
    • Atrial Systole: Blood moves through atrioventricular valves to ventricles, increasing ventricular volume.

Ventricular Activity

  • QRS Complex:
    • Represents ventricular depolarization.
    • Leads to ventricular contraction.
    • Ventricular Systole: Causes significant increase in ventricular pressure.
  • Isovolumetric Contraction:
    • Short phase where ventricular volume remains constant.
    • All heart valves are closed.
  • Semilunar Valve Opening:
    • Opens when ventricular pressure exceeds aortic pressure (approx. 80 mmHg).
    • Ejection Phase:
      • Blood is ejected from ventricles.
      • Ventricular volume decreases.

Ventricular Relaxation

  • T Wave:
    • Represents ventricular repolarization.
    • Ventricles relax, pressure decreases.
  • Isovolumetric Relaxation:
    • Ventricles relax while valves remain closed.
    • Pressure in ventricles drops below atrial pressure.
    • Atrioventricular valves open, blood passively fills ventricles.

Phonocardiogram

  • Heart Sounds:
    • "Lub" (First Sound): Atrioventricular valves closing during ventricular contraction.
    • "Dub" (Second Sound): Semilunar valves closing during ventricular relaxation.

Conclusion

  • Key Understanding: The cardiac cycle is a coordinated sequence of electrical and mechanical events resulting in blood flow through the heart.
  • Recommendation: Rewatch or pause the lecture for further clarification as needed.
  • Note: This summary is for educational purposes and reflects the main points discussed in the lecture.