mass transport

• The function of red blood cells is to transport oxygen throughout the blood, and they contain haemoglobin to do this.
• Haemoglobin structure

  Quaternary structure with 4 polypeptide chains, each containing a haem group with iron that binds to oxygen
• Affinity


  The ability of haemoglobin to attract and bind oxygen
• Saturation


  The maximum amount of oxygen that haemoglobin can bind to
• Loading/Association


  When oxygen is binding to haemoglobin
• Unloading/Dissociation


  When oxygen is detaching from haemoglobin
• Oxyhaemoglobin dissociation curve


  • Sigmoid (S-shaped) curve showing haemoglobin's affinity for oxygen at different partial pressures
  • High partial pressure = high affinity and saturation (e.g. alveoli)
  • Low partial pressure = lower affinity and saturation (e.g. respiring tissues)
• Cooperative binding


  The first oxygen binds with difficulty, but then subsequent oxygens bind more easily as the haemoglobin shape changes
• The Bohr effect is when a high carbon dioxide concentration causes the oxyhaemoglobin curve to shift to the right. The affinity for oxygen decreases because the acidic carbon dioxide changes the shape of the haemoglobin slightly.
• Haemoglobin adaptations in different animals

  • Fetal haemoglobin has higher affinity to extract oxygen from mother's blood
  • Llama haemoglobin has higher affinity for oxygen at high altitudes
  • Dove haemoglobin has lower affinity to readily unload oxygen for high metabolic needs
  • Earthworm haemoglobin has higher affinity to extract oxygen in low oxygen environments
• When there is a low partial pressure of carbon dioxide (e.g. in the alveoli) the curve shifts to the left as there is increased affinity, and therefore more oxygen is loaded.
• When there is a high partial pressure of carbon dioxide (e.g. in respiring tissues) the curve shifts to the left as there is decreased affinity, and therefore more oxygen is unloaded.