Oxygen and carbon dioxide transport

• Oxygen affinity


  ease with which Hb (haemoglobin) binds/unbinds to oxygen
• partial pressure of oxygen


  pressure exerted by oxygen
• words

  association - loading of oxygen

  dissociation - unloading of oxygen

  cooperative binding - binding becomes easier as more molecules bind
• Haemoglobin


  • a conjugated protein with a quaternary structure
  • large, globular, soluble
  • combines reversibly with oxygen (four molecules)
• Haemoglobin + oxygen -> oxyhaemoglobin


  Hb + 4O2 -> Hb(O2)4
• At the lungs 


  • association
  • high partial pressure of oxygen
  • there is a steep concentration gradient (alveoli->erythrocytes)
  • Hb has a high affinity for oxygen so it binds easily, and cooperative binding
• at the tissues

  • oxygen is used in respiration, lowering the partial pressure
  • low partial pressure of oxygen, haemoglobin has a low affinity for oxygen, making it easier to dissociate
• Foetal haemoglobin


  • has a higher affinity for oxygen, at the same partial pressures
  • this means it is a better competitor for any available oxygen at the placenta so the oxygen dissociates from the mothers haemoglobin and associates to the foetal haemoglobin
  • foetal curve shifts to left of adult
• Myoglobin


  • even higher affinity of oxygen
  • only releases oxygen at low partial pressures
  • found in skeletal muscles
  • even further left of adult
• $CO_2\$transport


  • 5% dissolved in plasm
  • 10% combined with haemoglobin to form carbamino-haemoglobin
  • 85% transported as HCO3- in plasma
• Bicarbonate for transport

  • forwards reaction is for loading
  • reverse reaction is for offloading

  A) carbonic acid

  B) bicarbonate

  C) carbon dioxide

  D) water

  
• Bicarbonate for transport

  • HCO3- is moved to be transported in plasma
  • Cl- moves into erythrocytes to balance charges
  • CARBONIC ANHYDRASE ENZYME INVOLVED
  • reaction occurs in erythrocytes
• carbon dioxide at the lungs

  • HCO3- changes to back to carbonic acid and then to CO2 and H2O
  • steep concentration gradient from blood -> alveolus
• Haemoglobinic acid


  • H+ causes a decrease in pH in erythrocytes
  • HHb forms as haemoglobin is now available as oxygen has dissociated
• Oxygen dissociation curve

  A) myoglobin

  B) foetal

  
• Bohr effect/shift:


  • higher partial pressure of carbon dioxide causes a lower affinity of oxygen
  • oxygen dissociation curve shifts RIGHT
  • as H+ ions are bound to Hb to form haemoglobinic acid, it is harder for oxygen to associate with it
  • this means that when more active, oxygen is offloaded more effectively as it is needed
• Carbon monoxide


  • combines with haemoglobin to form carboxyhaemoglobin
  • has a higher affinity compared to oxygen
  • so carbon monoxide poisoning