Dissolved in plasma (10%)
• Bound to Hb (20%)
• Bicarbonate (70%)
– At the tissue:
H+ binds to Hb
HCO3– diffuses out of RBC into plasma
Cl– diffuses into RBC (chloride shift)
– At the lung:
O2 binds to Hb (drives off H+)
Reaction reverses to release CO2