Notes on Cardiac Cycle Lecture

Introduction

• Speaker: Leslie Samuel from Interactive Biology
• Topic: Understanding the cardiac cycle, from the start of one heartbeat to the next
• Objective: Make understanding the cardiac cycle simpler and more accessible

Cardiac Cycle Overview

• Definition: Sequence of events in one heartbeat
• Phases:
  • Blood enters the heart via the atria
  • Atria contract, pushing blood into ventricles
  • Ventricles contract, pushing blood out of the heart

Electrocardiogram (ECG)

• Purpose: Shows electrical signals responsible for heartbeats
• Key Waves:
  • P Wave: Atrial depolarization leading to atrial contraction
  • QRS Complex: Ventricular depolarization leading to ventricular contraction
  • T Wave: Ventricular repolarization leading to relaxation

Atrial Systole

• Event: Atria contract
• Effect: Increases atrial pressure
• Blood Flow: Blood moves through atrioventricular valves into ventricles
• Ventricular Volume: Increases as ventricles fill with blood

Ventricular Systole

• Event: Ventricles contract
• Initial Phase: Isovolumetric contraction
  • Definition: Volume remains constant as all valves are closed
  • Result: Significant increase in ventricular pressure
• Ejection Phase:
  • Trigger: Ventricular pressure exceeds aortic pressure (~80 mmHg)
  • Action: Semilunar valve opens, blood ejected into aorta
  • Ventricular Volume: Decreases as blood is pumped out

Ventricular Repolarization

• Event: Ventricles relax
• Phases:
  • Isovolumetric relaxation (valves closed, ventricles relaxing)
  • Atrioventricular valves open once ventricular pressure is lower than atrial pressure
  • Passive filling of ventricles resumes

Heart Sounds

• Phonocardiogram: Records heart sounds
• Sounds:
  • "Lub": Closure of atrioventricular valves (post-QRS complex)
  • "Dub": Closure of semilunar valves (post-T wave)

Conclusion

• Understanding the Cycle: Rewatch and pause video for clarity
• Speaker's Message: Aim to make biology fun and accessible

Tips for Understanding

• Follow along with an ECG chart
• Relate events in the cycle to the corresponding heart sounds
• Review concepts of pressure changes and valve functions in the heart