Acid-Base Balance and Buffers
Buffer:
 a system consisting of a weak acid and a
weak base
 designed to prevent large shifts in pH which
could be harmful or potentially fatal to the
body
Recall: acids tend to give up H+ ions
bases tend to accept H+ ions
In the body a common buffer system uses
Carbonic acid H2CO3
and
Bicarbonate
HCO3When CO2 dissolves in our blood plasma we get
carbonic acid:
CO2 + H2O
H2CO3
HCO3- + H+
This can result in excess H+ ions, depending
on CO2 levels. Our kidneys regulate the
amount of bicarbonate in the body and have
excess HCO3- available to “mop up” the extra
H+ ions. This prevents wild pH shifts.
Excess H+ ions in the blood will trigger
increased respiration to reduce the acidity and
increase the pH of the blood.
If CO2 levels are too low, as in hyperventilation,
then bicarbonate ions (HCO3-) don’t have many
H+ ions to bind. The kidneys will eliminate
excess HCO3- in the urine.