Phosphoric acid is triprotic weak acid and has a pKa value for each of the three dissociations: Phosphates are important buffers intracellularly and in urine where their concentration is higher. The concentration of phosphate in the blood is so low that it is quantitatively unimportant. The phosphate buffer system is NOT an important blood buffer as its concentration is too low This shift in meaning of buffering can be confusing because the word buffering is mostly used in speech and in articles without the qualification of either 'physicochemical' or 'physiological' (or some qualifying word). Note: This use of the word buffering is in the broader sense of something that resists change in a property, and is different from the definition of buffering (or 'physiological buffering') given at the top of this page. The adjustment of pCO 2 by change in alveolar ventilation has been referred to as physiological buffering. The excretion of CO 2 via the lungs is the key thing because of the rapidity of the response. The system is more complex as it is open at both ends (meaning both and pCO 2 can be adjusted) and this greatly increases the buffering effectiveness of this system.

On chemical grounds, a substance with a pKa of 6.1 should not be a good buffer at a pH of 7.4 if it were a simple buffer. The distinction between pKa and p'Ka is usually forgotten and the Henderson-Hasselbalch equation is always written with pKa

Isfv physiology