Cardiovascular System Review

Heart Conduction System

• Sinus Node (SA node)
  • Initiates electrical impulse
  • Stimulates atria to depolarize and contract
• Atrioventricular Node (AV node)
  • Delays impulse allowing atrial blood to empty into ventricles
• Bundle of His
  • Transmits impulse from AV node to left and right bundle branches
• Purkinje Fibers
  • Depolarize myocardium
  • Trigger ventricular contraction

Cardiac Function

Cardiac Cycle

• Diastole: Ventricles and atria are relaxed and filling with blood
• Systole: Ventricles and atria contract and eject blood
• Time spent: 2/3 in diastole, 1/3 in systole

Key Terms

• Cardiac Output (CO)
  • Volume of blood ejected from the left ventricle per minute
  • Formula: CO = Heart Rate (HR) x Stroke Volume (SV)
  • Normal range for adults: 4-8 liters/minute
• Left Ventricular Ejection Fraction (LVEF)
  • Percentage of blood leaving the left ventricle during contraction
  • Normal range for adults: 55-70%
• Preload
  • Volume of blood in ventricles at end of diastole
  • Influences myocardial fiber stretch
• Afterload
  • Peripheral resistance the left ventricle must overcome to eject blood into systemic circulation
  • Important in managing heart failure

Blood Pressure (BP)

• Systolic BP: Pressure exerted during left ventricular contraction
• Diastolic BP: Pressure exerted during left ventricular relaxation (diastole)
• Regulation: Controlled by the autonomic nervous system
  • Receptor Types: Baroreceptors, Chemoreceptors, Stretch receptors

Quiz Questions

1. How do you calculate cardiac output?

• Cardiac output = Heart rate x Stroke volume

2. What is the volume of blood in the ventricles at the end of diastole called?

• Answer: Preload

3. What is the percentage of blood leaving the left ventricle each time it contracts called?

• Answer: Left ventricular ejection fraction (LVEF)

Next Steps

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