Basic Concepts in Clinical Biochemistry-A Practical Guide.7z

6.5 Physiological Buffers in the Human Body................

In thefirst instance, pH in the human body is maintained by physiological buffers.
Buffers may be intracellular and extracellular. Different buffer systems work in
correlation with one another. It means that changes in one buffer system lead to
changes in another. Various metabolic processes in body produce substantial
amounts of acids and bases. The production of these acids and bases may disturb
the blood pH. The normal blood pH is 7.4, and it is regulated very precisely. Various
conditions such as uncontrolled diabetes mellitus, nephritis, vomiting, diarrhea, etc.
cause change in blood pH. The physiological buffers help effectively to regulate
blood pH and maintain acid-base balance of body which if disturbed can disturb
metabolic processes.
The main physiological buffers in our body are the following:

1.Carbonate-bicarbonate buffer: It is the most important extracellular buffer and
has the largest buffering capacity. It is present in high concentration in plasma and
acts in cooperation with other buffers. It also plays an important role in the red
blood cells.
2.Hemoglobin buffer: It is the main intracellular buffer of the blood and regulates
blood pH by the removal of hydrogen ions from blood cells.
3.Protein buffer: It is an extracellular buffer together with bicarbonate buffer,
represented by plasma proteins. The histidine content of proteins plays an impor-
tant role in its buffering ability due to its pKa very near to blood pH.
4.Phosphate buffer: This buffer takes part in hydrogen ion excretion in renal
tubules and is not of great importance in blood due to its less concentration
although it has pKa close to blood pH.

6.6 Preparation of Common Laboratory Buffers..............

6.6.1 0.2 M Acetate Buffer (pKa 4.86)

Acetate buffer is prepared by the mixing of acetic acid and sodium acetate.
Prepare 0.2 M acetic acid and 0.2 M sodium acetate solutions separately. Add two
solutions in different proportions to obtain various pH solutions.

S. no

Volume of

0.2 M

acetic acid

taken

Amount of 0.2 M

acetic acid in

used volume (μ

mole)

Volume of

0.2 M sodium

acetate taken

(ml)

Amount of 0.2 M

sodium acetate in

used volume (μ

mole)

Theoretical

pH

1. 46 9200 a 4 800 3.8a


2. 42 8400 8 1600 4.1


3. 38 7600 12 2400 4.3


4. 34 6800 16 3200 4.5


5. 30 6000 20 4000 4.6

6.6 Preparation of Common Laboratory Buffers 25