the heart

• what is the system called that the heart pumps blood around the body in?

  the double circulatory system
• how many times does the blood pass through the heart on each circuit?


  Twice
• how many chambers are in the heart?


  Four
• what are the four chambers in the heart?

  left and right atria

  left and right ventricles
• what does the left and right atria do?


  receives blood from veins
• what do the left and right ventricles do?


  pump blood out into arteries
• how does blood enter the heart?

  through the atria
• what does the atria do?


  contract and force blood into the ventricles
• what do the ventricles do?


  contract and force blood out of the heart
• what do valves do?


  make sure blood flows in the correct direction
• what is the natural resting heart rate controlled by?

  a group of cells located in the right atrium which acts as a pacemaker
• what are artificial pacemakers?


  electrical devices used to correct irregularities in the heart rate