NURS601 Week 1 Concept 3: Acid-base balance (too much/too little acid)
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Dependent on H+ concentration
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Normal pH: 7.35-7.45
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Alkalosis: 7.45-7.8
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Acidosis: 7-7.35
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Anything >7.8 or <7 is deadly
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Buffering is the primary regulator of acid-base balance.
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Buffers act chemically to change strong acids into weaker ones, or bind them to neutralise them
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Different buffer systems assume dominant roles in different parts of the body:
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Extracellular Fluid (ECF)
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Major buffer: Bicarbonate buffer system
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Minor buffers: Intracellular problems, Phosphate buffer system
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Blood
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Major buffers: Bicarb buffer system, Hemoglobin
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Minor buffers: Plasma proteins, Phosphate buffer system
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Intracellular fluid (ICF)
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Major buffers: Proteins, Phosphate
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Minor buffers: None
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Urine
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Major buffers: Ammonia, Phosphate
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Minor buffers: None
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Secretes free hydrogen ions into renal tubules
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Excretes weak acid
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Excretes HCO3 (if there is metabolic acidosis)
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Respiratory Acidosis
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Decreased pH, increased PaCO2, normal HCO3
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Respiratory Alkalosis
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Increased pH, decreased PaCO2, normal HCO3
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Metabolic Acidosis
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Decreased pH, normal PaCO3, decreased HCO3
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Metabolic Alkalosis
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Increased pH, normal PaCO2, increased HCO3
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Normal ABG figures
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pH
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7.35-7.45
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PO2
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80-100
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PCO2
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35-45
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HCO3
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22-28
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How is it maintained?
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Buffers
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Bicarbonate (HCO3) - reacts rapidly, less than an second. Chemically change strong aicds to weaker acids or bind to neutralise effect
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Resipratory system
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Reacts rapidly - seconds to minutes
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Renal system
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Reacts slowly - hours
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CO2 formed and excreted in lungs
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Lungs excrete CO2 + H2O as by-products of cellular metabolism
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CO2 is regarded as an acid
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Homeostasis cycle of CO2 in the body:
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During exercise or other activity, cell metabolism increases and produces more CO2, then:
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More CO2 dissolves in blood, forming carbonic acid which lowers blood pH slightly, then:
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Receptors in the brain sense the drop in pH and send nerve signals to increase breathing rate, then:
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Increased breathing rate quickly removes more CO2 from blood. Blood pH rises slightly, returning to normal - cycle starts again
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