Acid base balance - general concept and mechanism

Mechanism of regulation
First line of defence- Blood buffers
1. Bicarbonate
2. Phosphate
3. Protein
Second line of defence -Respiratory regulation
1. Hypoventilation
2. Hyperventilation
Third line of defence - Renal mechanism
1. Excretion of H+
2. Conservation of HCO3-
3. Excretion of titrable acid
4. Excretion of ammonium ions


Bicarbonate buffer
Major buffer in ECF
Bicarbonate: carbonic acid in a ratio of 20:1
pKa-6.1
It is main buffer system because
a. High HCO3 -concentration
b. Components are under physiological control, CO2 by lungs and HCO3- by kidneys

Phosphate buffer
Major intracellular buffer
Na2HPO4: NaH2PO4 in a ratio of 4
pKa-6.8
More potent because pKa value is nearer to the body pH

Protein buffers
Hemoglobin
Albumin
Imidazole group of histidine is the most effective contributor in this buffer system