Buffering of an acid load

The relative contributions of the bicarbonate and non-bicarbonate buffer systems depend on the nature of the acid load. If the load is due to carbon dioxide retention, the hydrogen ions produced by the addition of carbon dioxide to the blood cannot be buffered by the bicarbonate system. The reason is evident from examination of the chemical reaction  

ACID-BASE PHYSIOLOGY IN THE CONTEXT OF BODY FLUIDS 

So far in this book, the emphasis has been on the chemistry of acid-base balance. We now proceed to consider the relationship of the concentrations of the chemicals important in the context of acid-base balance to the composition of plasma. In the wider context of the physiology of body fluids such as extracellular and intracellular fluids, there are two constraints which are of importance. The first constraint is physico-chemical and applies to any aqueous fluid. It is called the principle of electroneutrality , which states that, in an aqueous solution, the number of positive charges equals the number of negative charges. For reference, this important principle is included in Table 5.3. 

The second constraint is physiological and arises from the fact that the membranes of animal cells are frail and can withstand no pressure difference across them. Consequently, if there exists any difference in osmotic pressure between intra and extracellular fluids, there will be a net movement of water across the cell membrane until the osmotic gradient is cancelled. This net movement of water causes the cell to swell or shrink. At equilibrium, i.e. if the cell volume is not changing, the osmotic pressures of intra- and extracellular fluids are equal. These two different constraints give rise to two different units for measuring concentrations. 

In a solution, the number of positive charges equals the number of negative charges. 

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Table 5.2 Whole-blood buffering of an acid load...

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