DR Medhat MRCP

Acid-base balance & its disturbance
Life is an acidogenic process
o Fat & carbohydrate metabolism CO2 (1500 mmol/day) washed by lungs.
H20
o Protein metabolism non-volatile acids (50-80mmol/day) washed by kidneys.
o H + ion concentration & blood and interstitial fluid PH should be maintained within
narrow optimal range suitable for vital processes eg enzymatic reactions,ms
contraction, nerve conduction,……etc
o Normal PH of arterial blood 7.35-7.45
o Normal PH of venous blood & interstitial fluid is less (7.37) due to extra CO2 added to
venous blood from tissue metabolism(= tidal CO2).
o PH is inversely proportional to H + ion concentration (normally 40 neq/L).
Acidemia : non compensated blood H + > 45 neq/L & PH < 7.35.
Acidosis : 1ry abnormal state of blood H + which if not compensated
Alkalemia : non-compensated H + < 35 neq/L & blood PH >7.45.
Alkalosis : 1ry abnormal state of blood H + which if not compensated
academia.
alkalemia.
Normal regulation of blood PH:
A) Physio-chemical regulation (buffer system) : rapid mechanism
‣ Buffer is a chemical substances that prevent large change in blood PH when an acid
or a base is added to the blood.
‣ Either blood buffers (all buffers) or tissue buffers (HB ,phosphate,protein buffers)
‣ It consists of : 1) weak acid + its salt with a strong base e.g
H 2 CO 3 + NaHCO 3 (bicarbonate buffer)
H 2 PO 4 + Na 2 HPO 4 (phosphate buffer)
2) HB buffer (main tissue buffer) : carry tidal CO2 as carbamino
compounds to lungs to be washed in gas exchange.
B) Physiological regulation : slow mechanism
1) Role of the respiration :
o PCO2 ++ respiratory centers hyperventilation & wash of exess CO2 &vice
versa.
o H + ion concentration in blood __ resp. centers & hypoventilation CO2
2) Role of the kidney:
- All parts of renal tubular system secrete H + ion into tubular fluid.
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