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This is on as a "work in progress" - it's a bit (a bit?!?!?!) ugly at the moment but I'll tidy it up later - honest



To fully understand these notes (if that is at all possible given the quality of them) you will need a diagram of an oxygen dissociation curves. A useful pdf document is available at www.curriculumpress.demon.co.uk/pdf/bio/09 oxygen curves.pdf



4 oxygen bind to 1 haemoglobin oxyhaemoglobin (oxygen to tissues)



haemoglobin can bind to carbon dioxide carboxyhaemoglobin (carbon dioxide to lungs)

at high oxygen conc (e.g. in lungs) almost all HB is oxyHb



at middle oxygen conc (e.g. in vein between lung and heart, and arteries between heart and tissues) still almost all oxyHb



at low oxygen conc (respiring tissues) oxygen dissociates



Why is curve S-shaped not straight line?

Each binding of an oxygen causes conformational change in Hb making next one bind more readily

except the last one which does not bind oxygen very readily



Bohr Effect



carbon dioxide causes oxygen to dissociate more readily shifts curve to right



Bohr effect is explained by chloride shift



  • respiring tissues produce carbon dioxide


  • carbon dioxide diffuses into plasma and then into erythrocyte


  • in erythrocyte some binds to Hb carboxyHb
  • Most combines with water carbonic acid (enzyme = carbonic anhydrase)
  • carbonic acid dissociates hydrogen ions and hydrogencarbonate ions
  • eventually hydrogencarbonate conc in erythrocyte exceeds conc in plasma
  • so hydrogencarbonate (negative ion) diffuses into plasma
  • so chloride ions diffuse into RBC to balance = chloride shift


  • this leaves free hydrogen ions in RBC lowering pH and effecting enzymes


  • so the hydrogen ions
  • react with oxyHb reduced haemoglobin (Hhb) and oxygen


  • hence oxygen dissociation increased if CO2 present = Bohr Effect


  • In lungs all reactions are reversed


Other curves



foetal Hb has greater affinity than maternal (curve to left)



myoglobin (pigment in muscle) has more affinity than Hb (curve to left) so retains oxygen until very low partial pressures - acts as an oxygen store for very strenuous exercise



llama shows left show so more oxygen loading at low partial pressures



increasing temperature reduces affinity (curve to right) this means that at active tissues (high temp) Hb unloads

 

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