The Respiratory System and Acid-Base Balance

Respiratory system does not respond as fast as the chemical buffer systems.

However, it has up to two times the buffering power of all of the chemical buffer systems combined. 

CO2 produced by the tissue cells enters the red blood cells and is converted to HCO3 ions as follows:

dissoc of carbonic acid.jpg

The first set of double arrows illustrates a reversible equilibrium between the dissolved carbon dioxide and the water on the left and carbonic acid on the right.

The second set of arrows shows a reversible equilibrium between carbonic acid on the left and hydrogen and bicarbonate ions on the right

Because of this relationship, an increase in any of these chemicals causes a shift in the opposite direction 

Note also that the right side of this equation is the same as that for the carbonic acid-bicarbonate buffer system

Under normal conditions, the volume of CO2 eliminated at the lungs is equal to the amount of CO2 produced at the tissues.

When the CO2 is unloaded at the lungs, the preceding equation flows to the left, and causes the H+ generated from the carbonic acid to transform back to water.

bicarb to co2.jpg

Because of the protein buffer system, the H+ generated by the CO2 transport system is not permitted to increase

Therefore, it has little or no effect on blood pH