The Heart

• What causes hydrostatic pressure in the circulatory system?

  Pumping from the heart (contraction of ventricles)
• What is the scientific term for the contraction of the heart?


  Systole
• What is the scientific term for the relaxation of the heart?

  Diastole
• What are the stages of the cardiac cycle?

  • Diastole
  • Atrial systole
  • Ventricular systole
• What happens during diastole in the cardiac cycle?

  Blood returns to the atria, pressure rises, atrioventricular valves open, and blood passes into the ventricles.
• What occurs when the pressure in the atria exceeds that in the ventricles during diastole?

  The atrioventricular valves open, allowing blood to pass into the ventricles.
• What happens to the muscular walls of the atria and ventricles during diastole?

  The muscular walls are relaxed.
• What causes the semi-lunar valves in the aorta and pulmonary artery to close during diastole?


  The relaxation of the ventricle walls causes a reduction in pressure within the ventricles.
• What initiates the heartbeat during atrial systole?


  The sinoatrial node located in the right atrium.
• What happens during atrial systole?


  The sinoatrial node sends an impulse across both atria, causing them to contract and push blood into the ventricles.
• What is the role of the atrioventricular node (AVN) during ventricular systole?

  The AVN picks up the impulse, delays it, and sends it down the septum in the Bundle of His.
• How do the ventricles contract during ventricular systole?

  The ventricles contract from the base upwards, pushing blood up through the arteries.
• What causes the AV valve to close during ventricular systole?

  The pressure in the ventricles becomes higher than that in the atria.
• What is the function of the Bundle of His?

  It transmits the impulse from the AVN down the septum to the ventricles.
• What is the definition of cardiac output?

  The volume of blood pumped by one ventricle of the heart in one minute.
• What are the two factors that determine cardiac output?


  Heart rate and stroke volume.
• What is the equation for cardiac output?

  Cardiac output = heart rate x stroke volume.
• How do valves prevent the backflow of blood?


  They only open one way and close when there is higher pressure in front of them.
• What is the role of atrioventricular valves?

  They stop blood from flowing back into the atria when the ventricles contract.
• When do the atrioventricular valves open and close?

  They open when pressure in the atria is greater than in the ventricles and close when pressure in the ventricles is greater than in the atria.
• What is the role of semi-lunar valves?


  They stop blood in the arteries from flowing back into the ventricles when the ventricles contract.
• When do the semi-lunar valves open and close?

  They open when pressure in the ventricles is greater than in the arteries and close when pressure in the arteries is greater than in the ventricles.
• What are pocket valves?

  Valves in the veins.
• Why is the pressure in the atrium always low?

  Because they have thin walls.
• What feature of the aorta allows it to maintain high pressure?

  The elasticity of its walls creates a recoil action that keeps pressure high.