• Carbon Dioxide causes pH to decrease
  • Fetal Hb has a higher affinity for oxygen than adult Hb.
  • Bohr shift
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  • Created by: claris
  • Created on: 21-04-11 23:52

  • Carbon Dioxide causes pH to decrease
  • Higher respiration=more CO2 in tissues= lower pH= greater change in shape of haemoglobin= so oxygen is unloaded more readily= so more O2 available for respiration
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CO2 Concentration Affects Oxygen Unloading.

Hb gives up oxygen more readily at  a higher pCO2.

When cells respire, they produce CO2, which raises pCO2 and increases rate of O2 unloading.

This means respiring tissues are supplied with plenty of O2, at a faster rate, meaning cells respire faster.

  • Alveoli have high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin. 
  • Respiring cells use up oxygen, which lowers the pO2
  • Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads oxygen
  • Haemoglobin returns to the lungs to pickup more oxygen.
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  • Fetal Hb has a higher affinity for oxygen than adult Hb.
  • Fetus gets blood form mother’s blood, across the placenta.
  •  By the time the mother’s blood reaches the placenta, the pO2 is lower, as oxygen has already been used up around the body.
  • For fetus to get enough oxygen to survive, Hb has to have a higher affinity for oxygen.

At the same pO2, fetal Hb will be more saturated than Adult Hb.

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  • The Bohr Shift 
  • At the respiring tissues, there is a high pCO2 and a low pO2.
  • As a result haemoglobin's affinity for oxygen is reduced, meaning oxygen readily dissociates from Hb at the respiring tissues.


  • Graph S-shaped because when Hb combines with first O2 molecule, shape alters in way which makes it easier for other molecules to join too.

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