The Lungs and Acid-Base Balance

Hemoglobin acts as a buffer inside the RBCs. When CO2 goes into bicarbonate within the cells,

there are hydrogen ions made as part of this that could greatly affect the pH if it weren’t for the

buffering power of the hemoglobin molecule. Hemoglobin will take up the hydrogen ion,

reducing itself, and dissociating oxygen. The pH within the cells is maintained. The reverse of

this process happens in the lungs, where CO2 gas is made and exhaled, water is created out of

this, and oxygen binds to the hemoglobin protein.

Phosphate buffers involve the weak acid (sodium dihydrogen phosphate) and the weak base

(sodium monohydrogen phosphate). These will flip back and forth, taking up hydrogen ions or

hydroxyl ions in order to maintain the pH of the bloodstream.

Bicarbonate is a major buffer in the bloodstream. It is regulated by sodium, which is also the

case with the phosphate buffering system. Sodium bicarbonate is a weak base, while carbonic

acid is a weak acid. There is a ratio of bicarbonate ions to carbonic acid in the bloodstream that

is about 20:1 to keep the pH within the normal range. What this means is that, as a system, it

protects better against an acid environment than it does an alkaline environment, which is a

good thing because most metabolic wastes are acidic in nature.

The carbonic acid level is most closely associated with the CO2 level in the bloodstream.

Throughout the lung tissue, carbonic acid is dissociated through the action of carbonic

anhydrase to make CO2 and water. The level of bicarbonate in the bloodstream is controlled by

the kidneys, while the level of CO2 is controlled by the lungs. Bicarbonate is a significant buffer

as a weak base in the interstitial fluid in the tissues of the body.

THE LUNGS AND ACID-BASE BALANCE

The lungs participate in acid-base balance to a significant degree by regulating the amount of

carbonic acid in the bloodstream. The levels of CO2 and carbonic acid go together so as the CO2

level increases, so does the carbonic acid level. The exhalation of CO2 results in a loss of

carbonic acid concentration and raises the pH; the holding onto CO2 results in a gain of

carbonic acid concentration and lowers the pH level. This can happen really quickly and is the