The Heart

• The circulatory system is made up of the heart, blood vessels and blood
• Humans have a double circulatory system:

  • the right ventricle pumps deoxygenated blood to the lungs to take in oxygen, then the blood returns to the heart
  • the left ventricle pumps oxygenated blood around all the other organs of the body, which then gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped to the lungs again
• Double circulatory system

  two circuits joined together
• The heart is a pumping organ that keeps blood flowing around the body
• The walls of the heart are mostly made of muscle tissue
• The heart has valves to make sure that the blood flows in the right direction - they prevent it flowing backwards
• The heart has 4 chambers:

  • right atrium
  • right ventricle
  • left atrium
  • left ventricle
• 1. blood flows into the 2 atria from the vena cava and the pulmonary vein
  2. the atria contract, pushing the blood into the ventricles
  3. the ventricles contract, forcing the blood into the pulmonary artery and the aorta, out of the heart
  4. the blood then flows to the organs through arteries and returns through veins
  5. the atria fill again and the whole cycle starts over
• The heart needs its own supply of oxygenated blood
• Coronary arteries branch off the aorta and surround the heart, making sure it gets all the oxygenated blood it needs
• Your resting heart rate is controlled by a group of cells in the right atrium wall that act as a pacemaker
• Pacemaker cells produce a small electric impulse which spreads to the surrounding muscle cells, causing them to contract
• An artificial pacemaker is often used to control heartbeat if the natural pacemaker cells don't work properly (e.g. irregular heartbeat)
• Artificial pacemaker

  a small device implanted under the skin that has a wire going to the heart and produces an electric current to keep the heart beating regularly