The Circulatory System

• • The circulatory system is made up of the heart, blood vessels and blood
  • Humans have a double circulatory system, which is two circuits joined together
• What happens in the first circuit:

  • Heart pumps deoxygenated blood to gas exchange surfaces in the lungs to take in oxygen.
  • The oxygenated blood then returns to the heart
• What happens in the second circuit:

  • Oxygenated blood is pumped around the body and gives up all its oxygen at body cells
  • Blood returns to the heart to be pumped back to the lungs
• Advantage of mammals having a double circulatory system:

  • Blood returning to the heart after picking up oxygen at the lungs means it can be pumped around the body at a higher pressure. This increases the rate of blood flow to tissues so more oxygen can be delivered to cells
  • This is important for mammals as their cells require a lot of oxygen to maintain body temperature
• Diagram of the heart

  A) pulmonary artery

  B) pulmonary vein

  C) aorta

  D) vena cava

  E) tricuspid valve

  F) bicuspid valve

  G) semi-lunar valves

  H) right atrium

  I) left atrium

  J) right ventricle

  K) left ventricle

  
• The blood has valves to make sure the blood flows in one direction only. When the ventricles contract, the tricuspid and bicuspid valves close and the semi-lunar valves open
• • Blood flows into the heart from the vena cava and the pulmonary vein
  • The atria contract, forcing blood into the ventricles
  • The ventricles contract and semi-lunar valves open, forcing blood into the aorta and pulmonary artery, out of the heart
• After the blood leaves through the aorta or pulmonary arteries, blood flows into organs through arteries and return back to the heart through the veins

  • The atria fill again and the whole cycle starts over
• The heart is made up of cardiac muscle which contain lots of mitochondria to provide cells with ATP. Muscle cells also need their own blood supply to deliver nutrients and oxygen to keep the heart beating
• Blood is supplied to the heart by two coronary arteries, which branch from the base of the aorta
• • The aorta carries oxygenated blood from the heart to the body.
  • The vena cavae bring deoxygenated blood from the body back to the heart.
  • The pulmonary artery carries deoxygenated blood from the heart to the lungs.
  • The pulmonary veins carry oxygenated blood from the lungs back to the heart.