O2 Dissociation Curve

• O2 Dissociation Curve:

  • need to maintain 11 to 14 KPa to maintain concentration gradient so o2 can dissociate from haemoglobin and dissolve into tissue

  
• O2 only disassociates from Haemoglobin when surrounding plasma levels PaO2 have fallen below critical level
• Factors affecting Hb affinity O2:

  • Primarily affected by concentration PaO2
  • But also by
  • increase in CO2
  • increase in temperature
  • decrease in pH (acidosis)
  • increase in DPG (BPG) production - diphosphoglycerate
  • All of these factors are seen during exercise
• Changing Hb affinity for O2

  • Hb affinity for O2 decreases where PCO2 is high (tissues)
  • O2 dissociation curve shifts down and right
  • Facilitates:
  • O2 unloading & supply to the tissues
  • CO2 loading and removal from the tissues
  • Same occurs with:
  • increase in H+ / decrease in pH
  • increase in temperature
  • increase in DBG

  
• Diphosphoglycerate (23DPG)

  • DPG increases with:
  • Exercise
  • fever
  • acute altitude
  • acute hypoxia
  • chronic hypoxia
• The Plateau Phase:

  • After leaving the lungs, haemoglobin remains almost fully saturated as surrounding plasma levels of O2 remain high
  • Holds on to O2

  
• The steep slope:

  • At rest when PaO2 drops to 5.3 kPa -> Hb rapidly unloads O2
  • At the steep part of the slope small reductions in PO2 -> a large amount HbO2 off loading O2
  • So it can be used by tissues
  • EXERCISE = decrease in O2 tissue tension