<prompt> Best buffer of human blood:HCO3ChloridesHbPhosphates  <response>: Ans. a HCO3. Ref. Guyton physiology 11th ed. 385-387;Ganong, Physiology, 21st736 Phosphate buffer system is not important as an extracellular fluid buffer, it plays a major role in buffering renal tubular fluid and intracellular fluids. The buffer system that is quantitatively the most important in the extracellular fluid--the bicarbonate buffer system.Principal buffers in body fluids1. BloodH2CO3 K H HCO-3 HProt K H Prot- HHb K H Hb-2. Interstitial fluidH2 CO3 KH HCO 33. Intracellular fluidHProt KH HCO3, H2PO4 - KH- HPO4 2- For ECF especially blood plasma the predominant buffer is HCO3- Bicarbonate buffer. Bicarbonate thus acts as major buffers in ICW as well as ECW, but proton s are important buffers only in ICW. 