Haemoglobin & the transportation of oxygen

• What does 100% saturation mean?

  The haemoglobin is carrying its maximum amount of oxygen
• What are the units for oxygen saturation?

  SaO2%
• Blood leaving the lungs normally has a saturation of 95-99%
• What is partial pressure?

  The amount of oxygen in the tissue. It is measured in kPa
• Ventilation allows lung tissue to have a high partial pressure for oxygen
• What are the adaptations of erythrocytes?

  -biconcave shape: maximises surface area for gas exchange

  -small and flexible: can pass through narrow capillaries

  -no nucleus: more room to carry respiratory gases

  -packed with haemoglobin
• What is each haemoglobin molecule made of?

  4 globular proteins/polypeptide chains with 1 iron ion in each
• Haemoglobin can carry 4 oxygen molecules
• How does oxygen get from blood into respiring tissues?

  1. In the lungs, oxygen diffuses into blood plasma
  2. Oxygen passes down a concentration gradient and into erythrocytes
  3. Oxygen binds to haemoglobin to maintain this concentration gradient
  4. Oxygen binds to the 'haem' Fe2+ group of haemoglobin
  5. In respiring tissues, oxygen disassociates from oxyhaemoglobin
  6. Oxygen can then diffuse out of red blood cells and into the respiring cells
• Explain the shape of the first part of the Oxygen Diassociation Curve.?

  The first O2 molecule combines slowly with the first haem group, as it is at a low partial pressure of oxygen, so the first part of the graph is not very steep. The binding of O2 with the first haem group causes the shape of the whole haemoglobin molecule to change.
• Explain the shape of the second part of the Oxygen Disassociate Curve?

  Because of its altered shape, it is much easier for the 2nd and 3rd O2 molecule to bind to their haem groups, so the middle section of the graph becomes much steeper.
• Explain the shape of the third part of the Oxygen Disassociation Curve?

  The curve flattens off as it becomes harder for the last O2 molecule to combine with the last haem group, meaning it is very difficult to achieve 100% saturation of haemoglobin. This process is known as cooperative binding.