Foetal haemoglobin

• Oxygen saturation of haemoglobin

  Depends on the partial pressure of oxygen
• Partial pressure of oxygen is high (e.g. in alveoli)


  Haemoglobin has a high affinity for oxygen
• Haemoglobin has a high affinity for oxygen in the alveoli


  Haemoglobin loads oxygen rapidly, becoming around 97% saturated
• Partial pressure of oxygen falls (e.g. in actively respiring tissue)

  Oxygen affinity of haemoglobin decreases sharply
• Oxygen affinity of haemoglobin decreases


  Haemoglobin can now rapidly unload its oxygen to actively respiring tissue
• Bohr effect


  Carbon dioxide leads to a reduction in the oxygen affinity of haemoglobin causing the oxygen dissociation curve to shift to the right
• Bohr effect


  Causes the oxygen dissociation curve to shift to the right
• In the placenta, the foetal blood and maternal blood passed closely to each other but they did not mix
• Maternal blood has a higher level of oxygen than foetal blood


  Oxygen diffuses across the placenta and into the foetal blood
• Foetal haemoglobin


  Different to adult haemoglobin
• Oxygen dissociation curve for foetal haemoglobin

  Shifted to the left compared to adult haemoglobin
• Foetal haemoglobin


  Has a higher affinity for oxygen than adult haemoglobin
• Higher affinity of foetal haemoglobin for oxygen

  Increases the oxygen transfer across the placenta from maternal to foetal haemoglobin
• Oxygen affinity of foetal haemoglobin is only slightly greater than adult haemoglobin
• If foetal haemoglobin had very high oxygen affinity


  Could prevent it from unloading oxygen in foetal tissues
• Foetal haemoglobin


  Contains 2 polypeptide chains different to adult haemoglobin
• Different polypeptide chains in foetal haemoglobin

  Means it has a higher oxygen affinity
• Carbon dioxide from foetus diffuses into maternal blood

  Lowers the oxygen affinity of maternal haemoglobin
• Higher oxygen affinity of foetal haemoglobin

  Combined with lower oxygen affinity of maternal haemoglobin due to carbon dioxide, makes oxygen transfer from maternal to foetal blood extremely efficient