Physiology · Respiratory System

Carbon dioxide transport and Haldane effect

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Definition

CO2 is transported from tissues to lungs in three forms: dissolved in plasma, as bicarbonate ions, and as carbamino compounds.
The Haldane effect is the change in blood's CO2-carrying capacity with oxygenation: capacity rises as hemoglobin deoxygenates and falls as it oxygenates.

Modes of CO2 Transport

Modes of CO2 transport in blood

Form	% of total CO2	Mechanism
Dissolved in plasma	7%	Physically dissolved, per Henry's law
Bicarbonate ions (plasma and red cells)	70%	CO2 + H2O to H2CO3 (carbonic anhydrase) to H+ + HCO3−
Carbamino compounds	23%	CO2 binds free NH2 groups of Hb (carbaminohemoglobin), and in smaller amount plasma proteins

Form

Dissolved in plasma

% of total CO2: 7%
Mechanism: Physically dissolved, per Henry's law

Bicarbonate ions (plasma and red cells)

% of total CO2: 70%
Mechanism: CO2 + H2O to H2CO3 (carbonic anhydrase) to H+ + HCO3−

Carbamino compounds

% of total CO2: 23%
Mechanism: CO2 binds free NH2 groups of Hb (carbaminohemoglobin), and in smaller amount plasma proteins