Understanding the Cardiac Cycle

Introduction

• Presenter: Leslie Samuel, Interactive Biology
• Goal: Simplify the understanding of the cardiac cycle by breaking it down into parts.

What is the Cardiac Cycle?

• Definition: Everything from the beginning of one heartbeat to the next.
• Common misconception: Appears complicated due to detailed diagrams.
• Simplification: Break it down, understand each part separately.

Blood Flow in the Heart

• Blood Entry:
  • Left Side: Blood returns from the lungs.
  • Right Side: Blood returns from the rest of the body.
• Contractions:
  • Atria Contract: Push blood into ventricles.
  • Ventricles Contract: Push blood out of the heart.

Electrocardiogram (ECG)

• P Wave:
  • Represents atrial depolarization.
  • Causes atria to contract, increasing atrial pressure (Atrial Systole).
• QRS Complex:
  • Represents ventricular depolarization.
  • Ventricles contract, increasing ventricular pressure.
• T Wave:
  • Represents ventricular repolarization.
  • Ventricles relax, pressure decreases.

Cardiac Cycle Phases

• Atrial Systole:
  • Atria contract, blood moves through atrioventricular valves into ventricles.
  • Increases ventricular volume.
• Ventricular Systole:
  • Ventricles contract after QRS complex.
  • Isovolumetric Contraction: Short phase, ventricles contract with no volume change.
  • Semilunar Valve opens, blood ejected during the ejection stage.
• Ventricular Diastole (Isovolumetric Relaxation):
  • Ventricles relax, pressure decreases.
  • Atrioventricular valves reopen, ventricles fill passively with blood.

Phonocardiogram

• Heart Sounds:
  • First Sound: Lub (closure of atrioventricular valves during ventricular contraction).
  • Second Sound: Dub (closure of semilunar valves when ventricles relax).

Conclusion

• Understanding the cardiac cycle involves understanding the sequence of electrical and mechanical events.
• Heart sounds are indicators of valve actions during the cycle.
• Encouragement to rewatch for better comprehension.

Note: These notes are based on Leslie Samuel’s approach to explaining the cardiac cycle, emphasizing a simplified understanding.