the heart

• Humans have a double circulatory system made up of the heart, blood vessels and blood.
• In the first one the right ventricle pumps deoxygenated blood to the lungs to take in oxygen. The blood then returns to the heart
• in the second one the left ventricle pumps oxygenated blood around all the other organs. the blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart
• the heart has valves to make sure that blood flows in the right direction - they prevent backflow
• the heart uses four chambers the pump blood around:

  1. blood flows into the two atria from the vena cava and the pulmonary vein
  2. the atria contract pushing blood into the ventricles
  3. the ventricles contract forcing the blood into the pulmonary artery and the aorta, and out of the heart
  4. the blood flows to the organs through arteries and returns through veins
  5. the atria fill again and the cycle repeats
• the coronary arteries branch off the aorta and supply the heart with oxygenated blood