7.5 - The cardiac cycle

• What’s it called when the heart relaxes ?

  Diastole
• Does diastole occur in all chambers at once ?

  Yes
• Describe what occurs in the heart during diastole

  • Left and right atria fill with blood from the vena cava and pulmonary veins
  • Pressure increases in atria
  • When pressure in atria exceeds ventricular pressure the atrioventricular valves open
  • All walls relax so pressure in ventricles is reduced (less than in aorta and pulmonary artery)
  • So semi-lunar valves are closed
• Describe what happens in the heart during systole

  • Atrial systole forces blood into ventricles and atrioventricular valves open, but ventricles stay relaxed
  • A pause allows ventricles to fill, increasing pressure
  • Causes atrioventricular valves to close which prevents back flow
  • Ventricular systole occurs, once pressure exceeds the aorta and pulmonary artery, Semi-lunar valves open
  • Blood pumped out
• What are found in veins that prevent back flow of blood ?

  Pocket valves
• How are veins squeezed ?

  When skeletal muscles contract during movement
• What is a valve made of ?

  Flexible, fibrous cusp shaped tissue
• What are tendinous cords ?

  Inelastic cords of fibrous connective tissue that connect muscles to valve, prevent inversion
• What is cardiac output ?

  The volume of blood pumped by one ventricle in one minute
• Equation for cardiac output (CO) ?

  CO = stroke volume x heart rate