heart

• Circulatory system in fish

  Deoxygenated blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated, the oxygenated blood then passes straight from the gills to the organs where the oxygen diffuses out of the blood and into the body cells, the blood now returns to the heart
• Problem with single circulatory system in fish

  The blood loses a lot of pressure as it passes through the gills before reaching the organs, this means the blood travels to the organs relatively slowly so it cannot deliver a great deal of oxygen
• Circulatory system in humans

  Deoxygenated blood is pumped from the heart to the lungs where it collects oxygen, this oxygenated blood then returns to the heart, the heart now pumps the oxygenated blood to the organs where the blood transfers its oxygen to the body cells, the blood now returns back to the heart
• Benefit of double circulatory system in humans


  Because the blood passes through the heart twice, it can travel rapidly to the body cells delivering the oxygen that the cells need
• Heart

  • An organ consisting mainly of muscle tissue
  • The job of the heart is to pump blood around the body
• Heart chambers


  4 chambers - left atrium, right atrium, left ventricle, right ventricle
• Valves


  Separate the atria from the ventricles
• Blood vessels entering/leaving the heart

  • Vena cava (brings in oxygenated blood from the body)
  • Pulmonary artery (blood passes from the heart to the lungs)
  • Pulmonary vein (oxygenated blood passes from the lungs to the heart)
  • Aorta (blood is pumped from the heart to the body)
• Pattern of blood flow through the heart


  1. Blood enters the left and right atria

  2. Atria contract, forcing blood into the ventricles

  3. Ventricles contract, forcing blood out of the heart

  4. Valves prevent backflow into the atria
• Left ventricle


  • Has a thicker muscular wall than the right ventricle, as it pumps blood around the entire body and needs to provide greater force
• Coronary arteries


  Branch out of the aorta and spread into the heart muscle, their purpose is to supply oxygen to the muscle cells of the heart
• Pacemaker


  A group of cells found in the right atrium that control the natural resting heart rate
• Artificial pacemaker

  A small electrical device implanted by doctors to correct irregularities in the heart rate when the natural pacemaker stops working correctly