Question

Explain or respond to: physiological buffers are extremely important in maintaining pH equilibrium and hence good health for cells amd organs. lost the three primary "physiological buffers" and briefly describe how they maintain pH balance in the extracellular fluid (ICF) and extracellular fluid (ECF)

Answer 1

Buffer systems occur in -

i) Intracellular Fluid (ICF) which includes Phosphate buffer system and Protein Buffer systems.

ii) Extreacellular Fluid (ECF) which includes Carbonic acid - bicarbonate buffer systems and Protein Buffer systems.

Protein Buffer system also includes -

a) Hemoglobin buffer systems (RBCs only)

b) Amino acid buffers (all proteins)

c) Plasma protein buffers

1. Protein buffer systems:

– help regulate pH in ECF and ICF

– interact extensively with other buffer systems

2. Carbonic acid–bicarbonate buffer system:

– most important in ECF

3. Phosphate buffer system:

– buffers pH of ICF and urine

Extracellular Buffers

The most important buffer in the ECF and the body is HCO3- (bicarbonate) which combines with excess H+ ions to form carbonic acid.

Take for instance an acid load of H2SO4 produced via metabolism of methionine:

        H2SO4 + 2NaHCO3 → NA2SO4 + 2H2CO3 →2CO2 + 2H2O + NA2SO4.

Note in this buffering reaction that bicarbonate reacts with a strong acid to form a weaker acid(H2CO3) which then dissociates into CO2 and H2O. The CO2 produced here does not reform H2CO3 because it is then excreted by the lungs. Note that HCO3- is used up in this reaction. So that pH is not affected, the HCO3- used up in this process must be regenerated and the NA2SO4 must be excreted by the kidneys.

The CO2/HCO3- buffer system is considered very effective because of the vast quantity of bicarbonate in the body and the ability to excrete the CO2 formed via ventilation.

Other less important buffers in the ECF are plasma proteins and inorganic phosphates.

Intracellular Buffers

The primary intracellular buffers are proteins, organic and inorganic phosphates and in the RBC, hemoglobin (HB-). Whereas buffering by plasma HCO3- occur almost immediately, approximately 2-4 hours is required for buffering by cell buffers due to slow cell entry.

Hemoglobin is a very important buffer in RBCs, particularly in the role of carbonic acid buffering.

It should also be noted that transcellular uptake of hydrogen ions by cells result in the passage of Na+ and K+ ions out of cells to maintain electroneutrality. This process can substantially affect potassium balance as will be discussed later.