haemoglobin and oxygen

• • haemoglobin has a high affinity for oxygen - each molecule can carry 4 oxygen molecules
  • in the lungs, oxygen joins to the iron to form oxyhaemoglobin
  • this is a reversible reaction - when oxygen dissociates from it near the body cells, it turns back to haemoglobin
• the partial pressure of oxygen (pO2) is a measure of oxygen concentration --> the greater the concentration of dissolved oxygen in cells, the higher the pO2
• haemoglobin's affinity for oxygen varies depending on the pO2:

  • oxygen load onto haemoglobin where there's a high pO2
  • oxyhaemoglobin unloads it's oxygen where there's a low pO2
• • oxygen enters blood capillaries at the alveoli in the lungs. Alveoli have a high pO2 so oxygen loads onto haemoglobin
  • when cells respire, they use up O2 - this lowers the pO2. RBCs deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen
  • the haemoglobin then returns to the lungs to pick up more oxygen
• how does haemoglobin have positive cooperation?

  when oxygen binds, it changes the shape which increases its affinity for oxygen
• explain the 3 stages of the oxygen distribution curve:

  1. low pO2 = low affinity = oxygen is released instead of binding = low saturation
  2. higher pO2 = high affinity = more oxygen binds to Hb = easier to bind to other O2 (positive cooperation)
  3. very high pO2 = high affinity = Hb becomes fully saturated = oxyhaemoglobin
• explain the s shape of the oxygen distribution curve:

  • when Hb combines with the first O2 molecule its shape alters = easier for other molecules to join too
  • as the Hb becomes more saturated, it's harder for more O2 molecules to join
  • the steep bit is where a small change in pO2 causes a big change in the amount of oxygen carried by the Hb