the heart

• external structure of the heart

  A) superior vena cava

  B) inferior vena cava

  C) aorta

  D) right atrium

  E) coronary artery

  F) right ventricle

  G) vena cava

  H) pulmonary artery

  I) left atrium

  J) pulmonary veins

  K) left ventricle

  
• internal structure of the heart

  A) pulmonary artery

  B) superior vena cava

  C) inferior vena cava

  D) right atrium

  E) semi-lunar valve

  F) atrioventricular valve

  G) right ventricle

  H) left ventricle

  I) valve tendons

  J) atrioventricular valve

  K) semi-lunar valve

  L) left atrium

  M) pulmonary veins

  N) aorta

  
• The atrioventricular (AV) valves link the atria to the ventricles, and the semi-lunar (SL) valves link the ventricles to the pulmonary artery and aorta. they all stop blood flowing the wrong way.
• atrial systole 


  ventricles relax, atria contract
• atrial systole

  • The ventricles are relaxed
  • The atria contract, decreasing the volume of the chambers and increasing the pressure inside the chambers.
  • pushes the blood into the ventricles through the atrioventricular valves.
  • slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria.
• ventricular systole 


  ventricles contract, atria relax
• diastole 


  ventricles and atria relaxed
• ventricular systole

  • The atria relax.
  • The ventricles contract increasing their pressure.
  • The pressure becomes higher in the ventricles than the atria, which forces the AV valves shut to prevent back-flow.
  • The pressure in the ventricles is also higher than in the aorta and pulmonary artery, which forces open the SL valves and blood is forced out into these arteries.
• diastole

  • The ventricles and the atria both relax.
  • The higher pressure in the pulmonary artery and aorta closes the SL valves to prevent back-flow into the ventricles.
  • Blood returns to the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein.
  • In turn this starts to increase the pressure of the atria.
  • As the ventricles continue to relax, their pressure falls below the pressure of the atria and so the AV valves open.
  • This allows blood to flow passively into the ventricles from the atria.
  • The atria contract, and the whole process begins again.
• cardiac output = heart rate x strike volume
• heart rate 


  the number of beats per minute
• stroke volume 


  the volume of blood pumped during each heartbeat