Most important compensatory mechanism in metabolic acidosis
|B||Increased NH3 excretion by kidneys|
|C||Increased urinary phosphates|
|D||Increased HCO3 production|
Compensatory mechanism for metabolic Acidosis
a. The extra H+ ions of the body are tackled by the buffer of blood, notably by the HCO3- system. So, the fall of pH is not great but loss of plasma bicarbonate is considerable
b. Respiratory: - Hyperventilation → CO2 removed though lungs is not so great.
c. Renal —
A. The renal tubular cells secrete H+ into the tubular fluid in exchange for Na+, and for each H+ secreted, one Na+ and one HCO3+- are added to the blood.
B. In chronic Acidosis → NH3 excretion increases over period of days, further improving the renal
compensation of acidosis.
Compensation for metabolic acidosis includes:
A. Extracellular buffering primarily by HCO Intracellular buffering primarily by proteins and phosphate
B. Respiratory compensation by an increase in alveolar ventilation resulting in a decline in the CO2 tension.
C. Renal compensation by an increase in H excretion and an increase in HCO3- reabsorption.
Formation and Excretion of NH4+
a. The renal excretion of NH4+ causes the net addition of HCO3- to the plasma.
b. Under most conditions, the excretion of NH4+ is quantitatively more important to the acid- base balance of the body than is the excretion of titrable acid. (Titrable acid is largely attributed to conversion of HPO42- to H2PO4-.The normal kidney excrete almost twice as much acid combined with NH3+ (30-50 mEq/day) as titrable acid (10-30 meq/day) -
A. In chronic severe metabolic acidosis NH4+ serves as the major urinary buffer, and NH4+ excretion can increase from a normal value of 30 meq/day to 500 meq/day. However in chronic acidosis, the excretion of H2PO4- may increase by only 20-40 meq/day.
B. In diabetic ketoacidosis (metabolic acidosis) — the excretion of titratable acid may reach 75-250, whereas the excretion of acid combined with NH3+ may reach amounts of 300-500 meq/day. (Normal — 30-50).Now it is clear, from above discussion, the NH3 excretion by kidney, is the most important compensatory mechanism in metabolic acidosis.