Gas Exchange and
Transport
DANIEL CONDE PH.D.
NEW MEXICO STATE UNIVERSITY
McArdle, Katch, and Katch, 2015
Concentration and Partial Pressure of
Respired Gases
Partial pressure = Percentage of concentration of specific gas X Total pressure of
a gas
Dalton’s law
◦Total pressure = Sum of partial pressure of all gases in a mixture
Ambient Air
◦O2= 20.93% = ~ 159 mm Hg PO2
◦CO2= 0.03% = ~ 0.23 mm Hg PCO2
◦N2= 79.04% = ~ 600 mm Hg PN2
McArdle, Katch, and Katch, 2015
McArdle, Katch, and Katch, 2015
Concentration and Partial Pressure of
Respired Gases Cont.
Tracheal Air
◦Water vapor reduces the PO2in the trachea about 10 mm Hg to 149 mm Hg.
Alveolar Air
◦Alveolar air is altered by entry of CO2.
◦Average alveolar PO2= 103 mm Hg
McArdle, Katch, and Katch, 2015
McArdle, Katch, and Katch, 2015
Gas Movement in Air and Fluids
Henry’s law
◦Gases diffuse from high pressure to low pressure.
Diffusion rate depends upon
◦Pressure differential
◦Solubility of the gas in the fluid
Pressure differential
The difference in the pressure of specific gases from the capillary blood to
the alveoli dictates the direction of diffusion
McArdle, Katch, and Katch, 2015
