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Acid-Base Balance

Dr. Suzanah Abdul Rahman

Kulliyyah of Allied Health Sciences

International Islamic University Malaysia

Kuantan Campus

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Acid-Base Balance

Acid-base balance depends on the level of H+ ionsNormal cellular function requires maintenance of pH of systemic arterial blood between 7.35 and 7.45Metabolic reactions produce excess H+ which can quickly rise to lethal levelsRemoval of H+ from body fluids and elimination through important processes

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Acid-Base Balance

Major mechanisms

Buffer systemsExhalation of Carbon DioxideKidney excretion of H+

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Buffer Systems

Systems include protein buffer system, carbonic acid-bicarbonate buffer system & phosphate buffer systemRapid removal of H+ through binding of excess highly reactive H+ from solutionpH is raised but H+ is not eliminated from the bodyCovert strong acids & bases into weak acids and bases

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Protein Buffer System

Most abundant in intracellular fluid & blood plasmaBuffers both acids & basesImportant functional groups of protein are COOH & NH2 groupsCOOH releases H+ when pH risesNH2 combine with H+ when pH drops

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Protein Buffer System

Protein hemoglobin important buffer of H+ in RBCs

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Carbonic Acid- Bicarbonate Buffer System

HCO3- important in intracellular & extracellular fluidsKidney synthesize & also reabsorb filtered HCO3-Act as weak base to remove excess H+H2CO3 dissociates into H2O & CO2H2CO3 acts as a weak acid to provide H+ during shortageBuffer system cannot protect from pH changes when there is respiratory problems whereby there is shortage or excess of CO2

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Phosphate Buffer System

Phosphate major anions in intracellular fluids but not in extracellular fluidsHence important system in cytosolDihydrogen phosphate as weak acid buffering strong base as OH-Monohydrogen phosphate as a weak base buffering H+ released by e.g. HClH+ that is part of H2PO4- passes into urine and excreted in maintenance of blood pH

(weak base)

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Exhalation of Carbon Dioxide

Breathing helps maintain pH of body fluids!H2CO3 a volatile acid as it can be eliminated by exhalation of CO2Increased ventilation, increases CO2 exhalation decreasing H+ concentrationDoubled ventilation, pH 7.4 pH 7.63Ventilation reduced to one-quarter of normal, pH 7.4 pH 7.0pH & rate and depth of breathing operates via a negative feedback loop

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Exhalation of
Carbon Dioxide

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Kidney Excretion of H+

Metabolic reactions produce nonvolatile acids e.g. sulfuric acidRenal failure can cause build-up of non-volatile acids leading to deathSecretion of H+ at PCT and collecting ductsApical membrane of intercalated cells of collecting ducts have proton pumps that secrete H+ into tubular fluid Urine can be 1000 times more acidic than bloodSecreted H+ is buffered by ammonia to form ammonium ions and monohydrogen phosphate forming dihydrogen phosphateBoth ions cannot diffuse back into tubules cells hence they are excreted

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Kidney Excretion of H+

Secretion of H+

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Kidney Excretion of H+

Buffering of H+ in urine

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Acid-Base Imbalances

Normal pH range btw 7.35 and 7.45Below 7.35 acidosis/ acidemiaMajor physio effects depression of synaptic transmission leading to disorientation, coma & deathHigher than 7.45 alkalosisMajor physio effects CNS and peripheral nerves overexcitability causing nervousness, spasms, convulsion & deathBoth conditions can be countered with compensation mechanisms either respiratory or renal

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