Acid-base balance

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Acid-base Balance
R. C. Gupta M.D.
(Biochemistry) Jaipur, India
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Acids and bases
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• H2CO3 H HCO3
• HNO3 H NO3
• H3PO4 H H2PO4
• H2PO4 H HPO4
• Acid Proton Base

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Strength of acids
Acids, e.g. hydrochloric acid and carbonic
acid, dissociate into their component ions
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• HCl ? H Cl
• H2CO3 ? H HCO3

However, all acids do not dissociate to the same
extent
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pH scale
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pH log H
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Water dissociates into hydrogen ions
and hydroxyl ions


Ion product
of water (Kw) is Kw H
OH 10-14

In pure water, number of
hydrogen ions is equal to the number of hydroxyl
ions
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1 mol/litre 109 nanomol/litre
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pH H concentration
7.4 40 nanomol/litre
7.5 31 nanomol/litre
7.6 25 nanomol/litre
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Regulation of pH of body fluids
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EMB-RCG
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EMB-RCG
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Bicarbonate-carbonic acid buffer
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Phosphate buffer
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NaOH NaH2PO4 H2O Na2HPO4
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Proteins
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Haemoglobin
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EMB-RCG
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Respiratory regulation
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EMB-RCG
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Chemoreceptors are located in the aortic arch
and carotid sinus
They perceive changes in pH, pCO2 and pO2
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They transmit information to the respiratory
centre
Respiratory centre, accordingly, regulates the
rate and depth of respiration
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Renal regulation
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EMB-RCG
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Reabsorption of bicarbonate
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Acidification of monohydrogen phosphate
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Secretion of ammonia
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EMB-RCG
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EMB-RCG
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Renal mechanism tries to compensate respiratory
acidosis or alkalosis
Respiratory mechanism tries to compensate
metabolic acidosis or alkalosis
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EMB-RCG
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Respiratory acidosis
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Respiratory alkalosis
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Metabolic acidosis
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Metabolic acidosis with normal
anion gap
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Metabolic acidosis with increased anion gap
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The compensatory decrease in pCO2 is 1.25 mm of
Hg for every 1 mmol/L decrease in bicarbonate
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Metabolic alkalosis
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Blood chemistry in acid-base disorders
Disorder Blood pH Primary change Compensatory change
Respiratory acidosis ? pCO2 ? HCO3
Respiratory alkalosis ? pCO2 HCO3
Metabolic acidosis HCO3 pCO2
Metabolic alkalosis ? ? HCO3 ? pCO2
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Mixed acid-base disorders
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Thank you