The Heart and Circulation

• Fish have a single circulatory system.

  Deoxygenated blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated. The oxygenated blood now 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.

  
• Problems with single circulatory system:

  • blood looses a lot of pressure as it passes through the gills before reaching the organs
  • This means that the blood reaches the organs relatively slowly so it cannot deliver a great deal of oxygen.
• Humans have a double circulatory system.
• Human double circulatory system:

  1. deoxygenated blood is pumped from the heart to the lungs where it collects oxygen.
  2. Oxygenated blood returns to the heart
  3. The heart pumps oxygenated blood to the organs where the blood transfers its oxygen to the body cells
  4. The blood now returns back to the heart
• Benefit of double circulatory system:

  • because the blood passes through the heart twice, it can travel rapidly to the body cells, delivering the oxygen that the body cells need.
• The heart is an organ consisting mainly of muscle tissue. The heart pumps blood around the body.

  
• The heart has four champers:

  • left atrium
  • right atrium
  • left ventricle
  • right ventricle

  
• The atria are separated from the ventricles by valves.
• Diagrams of the heart always look back to front as they are drawn as if you are looking at a person.
• The vena cava brings in deoxygenised blood from the body.
• The blood passes from the heart to the lungs in the pulmonary artery.
• Oxygenated blood passes from the lungs to the heart in the pulmonary vein.
• Oxygenated blood is pumped from the heart to the body in the aorta.
• 1. blood enters the left atrium and the right atrium.
  2. The atria now contracts and the blood is forced into the ventricles.
  3. the ventricles now contract and force blood out of the heart.
  4. Valves stop the blood from flowing backwards into the stria when the ventricle contracts.
• The left side of the heart has a thicker muscular wall than the right side. This is because the left ventricle pumps blood around the entire body so it needs to provide a greater force.
• The coronary arteries branch out of the aorta and spread out into the heart muscle.
• The purpose of the coronary arteries is to provide oxygen to the muscle cells of the heart.
• The oxygen provided by the coronary artery is used in respiration to provide the energy for contractions.
• The natural, resting heart rate is controlled by the pacemaker which is located in the right atrium.

  
• Sometimes the pacemaker stops working correctly. In this case, doctors can implant and artificial pacemaker.
• An artificial pacemaker is a small electrical device and it corrects irregularities in the heart rate.