Intracellular the acidity of the solution: the lower

Intracellular and extracellular buffers are
substances that produce an immediate response to acid-base balance change.
Buffer are solutions that typically consist of an acid-base pair. ( weak acid
and its conjugate base ) .It will, therefore, react with strong acids or strong
bases by absorbing H+ ions or OH? ions, replacing the strong acids/ bases with
weak acids/ bases. Therefore, the buffer system will minimize changes in pH
near its equilibrium constant.

Several buffer pairs are observed in the body
fluids, however, the most significant buffer system is the HCO3?/CO2 buffer
system, described by the following equation :


As a result of an increase of hydrogen ions, the
equation is driven to the right and generates Carbon dioxide.Therefore when
bicarbonate ions react with hydrogen ions and result in a  carbonic acid, hydrogen ions are removed,
leading to changes in the ph. Likewise, excess carbonic acid can be converted
into CO2. Carbon dioxide concentrations are regulated by the respiratory system
H+ and HCO3? balance are regulated by renal system


The relationship between pH, bicarbonate
(HCO3?), and CO2 in the HCO3?/CO2 buffer system is described in the
Henderson–Hasselbach equation.



•    pH is
– {log} of molar concentration of H+ in the extracellular fluids. It indicates
the acidity of the solution: the lower the pH the greater the acidity.

•    pKa
H2CO3 is the carbonic acid dissociation constant, which is equal to 6.1.

HCO?3 indicates the concentration (moles/liter) of bicarbonate in the
blood plasma.


The equation evidence that acid-base equilibrium
depends on the proportion of PCO2 and HCO3?, not on the absolute value of
either one alone. Therefore, the greater the concentration of the weak acid in
the solution is, the lower the pH of the solution will be. Using this formula,
two variables can be applied to determine the third one.











Other significant physiologic buffers are intracellular organic and
inorganic phosphate system and protein buffer systems.

Proteins can operate as buffers as they are made up of amino acids which
contain positively charged amino groups (-NH2) 
and negatively charged carboxyl groups(-COOH). The charged regions of
the functional groups can bind to hydrogen ions and hydroxyl ions. As amino
acids are able to react with both acid and base,  consequently operate as buffers system.

Protein buffers in blood include hemoglobin (150g/l), which is an effective
buffer because of its presence in the red blood cells at highly elevated
concentrations.Histidine residues in hemoglobin are able to accept hydrogen
ions and therefore operate as buffers. It is important to mention that deoxygenated
hemoglobin is has a higher tendency to accept H+  than the oxygenated hemoglobin. The
hemoglobin is discussed in detail in a separate section.

The phosphate buffer system is not a relevant blood buffer, as the
phosphate concentration in the plasma is too low, However, it plays a critical
role in buffering intracellular fluids and urine where phosphate concentration
is higher.

Phosphate buffer system consists of mono-hydrogen phosphate ions (HPO4-2)
and dihydrogen phosphate ions (H2PO4-).When the buffer system comes in the
contact with a strong acid (ex, HCL), the base (HPO4) accepts the hydrogen and
convert it to H2PO4-.As a result, the strong acid(HCl), is replaced by a weak
acid, (NaH2PO4) and the decrease in pH is reduced.

When a strong base, NaOH(strong base), comes in contact with the buffer,
the OH- is buffered by the H2PO4- to form additional amounts of HPO4 and
produces water.