Intracellular the acidity of the solution: the lower

Intracellular and extracellular buffers aresubstances that produce an immediate response to acid-base balance change.Buffer are solutions that typically consist of an acid-base pair. ( weak acidand its conjugate base ) .It will, therefore, react with strong acids or strongbases by absorbing H+ ions or OH? ions, replacing the strong acids/ bases withweak acids/ bases. Therefore, the buffer system will minimize changes in pHnear its equilibrium constant.Several buffer pairs are observed in the bodyfluids, however, the most significant buffer system is the HCO3?/CO2 buffersystem, described by the following equation : As a result of an increase of hydrogen ions, theequation is driven to the right and generates Carbon dioxide.Therefore whenbicarbonate 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 convertedinto CO2. Carbon dioxide concentrations are regulated by the respiratory systemH+ 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 theHenderson–Hasselbach equation.  where:•    pH is- {log} of molar concentration of H+ in the extracellular fluids.

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It indicatesthe acidity of the solution: the lower the pH the greater the acidity.•    pKaH2CO3 is the carbonic acid dissociation constant, which is equal to 6.1.•   HCO?3 indicates the concentration (moles/liter) of bicarbonate in theblood plasma. The equation evidence that acid-base equilibriumdepends on the proportion of PCO2 and HCO3?, not on the absolute value ofeither one alone.

Therefore, the greater the concentration of the weak acid inthe 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 andinorganic phosphate system and protein buffer systems.Proteins can operate as buffers as they are made up of amino acids whichcontain positively charged amino groups (-NH2) and negatively charged carboxyl groups(-COOH).

The charged regions ofthe functional groups can bind to hydrogen ions and hydroxyl ions. As aminoacids 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 effectivebuffer because of its presence in the red blood cells at highly elevatedconcentrations.Histidine residues in hemoglobin are able to accept hydrogenions and therefore operate as buffers.

It is important to mention that deoxygenatedhemoglobin is has a higher tendency to accept H+  than the oxygenated hemoglobin. Thehemoglobin is discussed in detail in a separate section.The phosphate buffer system is not a relevant blood buffer, as thephosphate concentration in the plasma is too low, However, it plays a criticalrole in buffering intracellular fluids and urine where phosphate concentrationis higher.Phosphate buffer system consists of mono-hydrogen phosphate ions (HPO4-2)and dihydrogen phosphate ions (H2PO4-).When the buffer system comes in thecontact with a strong acid (ex, HCL), the base (HPO4) accepts the hydrogen andconvert it to H2PO4-.As a result, the strong acid(HCl), is replaced by a weakacid, (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 andproduces water.


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