As we now measure pH rather than quantitate the levels of base in the blood, pH status would be a more appropriate term than acid-base status. Such a solution contains both acidic and basic groups. A mixture of a weak acid or a weak base and a salt of that acid or base in solution is a buffer solution. A mixture of acetic acid and sodium acetate in water is a buffer solution. In this example Acetic Acid is the acid.
Acetate ion is the base.
The efficiency of a particular concentration of a buffer solution is greatest when it consists of equal quantities of the weak acid and the salt or weak base and the salt. Protein molecules contain acidic and basic groups. Therefore, protein solution is a buffer solution. The heterogeneous nature of protein and the multiple acidic and basic groups make protein solution a buffer without a single pK. Therefore, protein buffers are efficient over a wide pH range. In biological systems sodium bicarbonate does not act as a buffer since it will not diminish changes in pH if a base is added.