A-Level Biology: The Cardiac Cycle

Introduction

• Presenter: Miss Esther
• Topic: The Cardiac Cycle
• Focus: Volume and pressure changes, valve function
• Pre-requisite: Understanding heart structure

Overview of Heart Structures

• Four Chambers
  • Atria
  • Ventricles
• Four Major Blood Vessels
• Valves
  • Semilunar valves
  • Atrioventricular valves (bicuspid & tricuspid)
• Muscular Walls: Thickness is important for function

The Cardiac Cycle

• Controls blood flow direction and valve operation
• Three Stages:
  1. Diastole
  2. Atrial Systole
  3. Ventricular Systole
• Pronunciation Notes: diastole vs. distally, systole vs. systole

Stages of the Cardiac Cycle

Diastole

• Status: Both atria and ventricles relax
• Outcome: Blood flows into the atria, pressure rises as blood volume increases

Atrial Systole

• Status: Atria contract
• Effect: Increased pressure opens atrioventricular valves, blood moves into ventricles

Ventricular Systole

• Status: Ventricles contract after a short delay
• Effect: Thick muscular walls cause high pressure, forcing atrioventricular valves shut and semilunar valves open, blood exits through pulmonary artery and aorta

Cardiac Output

• Formula: Heart Rate x Stroke Volume
• Heart Rate: Beats per minute
• Stroke Volume: Blood volume per beat

Valve Functionality

• Purpose: Ensure unidirectional blood flow
• Operation:
  • Valves open when pressure behind is higher
  • Valves close when pressure in front is higher

Atrioventricular Valves

• Open: Higher atrial pressure than ventricular
• Close: Higher ventricular pressure than atrial

Semilunar Valves

• Open: Higher ventricular pressure than arterial
• Close: Higher arterial pressure than ventricular

Graphical Interpretation

• Common Task: Identify valve function on pressure change graphs
• Key Points:
  • Semilunar valves open/close based on ventricular and aortic pressures
  • Atrioventricular valves open/close based on atrial and ventricular pressures

Summary Table

• Atrial Systole: Atria contract, volume decrease, pressure increase
• Ventricular Systole: Ventricles contract, large volume and pressure change
• Diastole: Relaxation leads to volume increase and gradual pressure rise

Conclusion

• Three Stages: Diastole, Atrial Systole, Ventricular Systole
• Function: Pressure and volume changes control valve operation
• Graph Representation: Visual aid to identify valve status

Additional Resources

• Practice Questions: Available on Miss Esther's website under Topic 3

Engagement

• Feedback: Like and subscribe if the video was helpful

Note: Understanding these processes and their graphical representation is crucial for mastering the cardiac cycle's physiological dynamics.