O2 transport

• O2 in solution: o2 is dissolved in plasma  • PaO2 is concentration O2 in plasma  

  • 1.5% O2 is Tx in plasma  

  • Inefficient means of Tx because o2 isn't soluble  
• O2 and Hb: 

  • 98% O2 binds to Hb (quick process) 
• For o2 to be used it has to come away from haemoglobin, and dissolve in the plasma so it can diffuse to the tissues  
•  

  Hb’s changing affinity for O2: 

  • Maximises O2 binding at lungs  

  • Facilitates O2 release at tissues  

  • Produces sigmoid shaped oxygen dissociation curve 
• Normal o2 range is 11-14 Kilo pascals  
• The Plateau Phase: 

  • After leaving lung Hb 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 -->↓ O2 tissue tension 
• 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 -->↓ O2 tissue tension 
• Factors affecting Hb affinity O2: • Primarily affected by concentration PO2 • But also by  

    – CO2  

    – temperature  

    – pH  

    – DPG (BPG) - diphosphoglycerate 
• Changing Hb affinity for O2: • Hb affinity for O2 ↓ where PCO2 is high (tissues)  

  • O2 dissociation curve --> shifts ↓ & right  

  • Facilitates – O2 unloading & supply to the tissues – CO2 loading and removal from the tissues  

  • Same occurs with ↑H+ ( ↓pH)  

  • ↑ temperature  

  • ↑DBG 
• Diphosphoglycerate (23DPG): by product of red blood cell metabolism  

  • DPG increases with  

  – Exercise  

  – fever  

  – acute altitude  

  – acute hypoxia  

  – chronic hypoxia