Electrolytes, Water and Acidbase balance

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Electrolytes, Water and Acid-base balance
Dr. Imran Mirza Department of Laboratory Medicine
Pathology University of Alberta
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Learning Objectives

• Understand the body water compartments, and the
  associated electrolytes
• Explain how the respiratory and renal systems
  participate in buffering of the bodies pH
• Describe the terms respiratory acidosis/alkalosis
  and metabolic acidosis/alkalosis
• Explain how the body compensates for pH
  imbalances

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Electrolytes, H2O and Acid-base balance

• Body water contains dissolved mineral salts
  electrolytes
• Dissociate in solution
• Cations positively charged ions
• Anions negatively charged ions

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Intracellular and Extracellular Fluid

• Intracellular fluids (37 of total body water)
  are separated from interstitial fluid (63 of
  total body water) by a cell membrane
• Freely permeable to water
• Na and Cl- chief extracellular ions
• K and PO42- principal intracellular ions

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Regulation of Body Fluid and Electrolyte
Concentration

• Water Balance total water intake total water
  loss (output)
• Disturbances of water balance
• Dehydration loss from the GI tact
• Overhydration excess intravenous fluids

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Regulation of Body Fluid and Electrolyte
Concentration

• Disturbances of electrolyte balance
• Vomiting for diarrhea
• Diuretics

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Acid-Base Balance

• The body produces large amounts of acid but body
  fluids remain slightly alkaline.
• The pH is maintained within the narrow range of
  7.38 to 7.42.
• The major buffer system is the sodium
  bicarbonate-carbonic acid system.

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Regulatory Mechanisms that Maintain pH

• Buffer systems of the blood
• Concentration of carbonic acid controlled by the
  lungs
• In equilibrium with carbon dioxide in the
  pulmonary alveoli
• Concentration of bicarbonate controlled by the
  kidneys
• Can reabsorb bicarbonate
• Can synthesize bicarbonate (on next slide)

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Relation Between pH and Ratio of Buffer Components

• pH depends on ratio of bicarbonate to carbonic
  acid
• Carbonic acid in equilibrium with bicarbonate
• Normal ratio
• 20 parts sodium bicarbonate
• 1 part carbonic acid

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Acidosis
Alkalosis
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Mechanisms of Acid-Base Disturbances

• Metabolic Acidosis excess acid depletes HCO3
• Respiratory Acidosis decrease CO2 excretion by
  lungs
• Metabolic Alkalosis excess plasma bicarbonate
• Respiratory Alkalosis hyperventilation ? PCO2

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Mechanisms of Acid-Base Disturbances

• Metabolic acidosis
• Three major sources are
• Renal failure unable to secrete acidic waste
• Ketosis overproduction of ketones in untreated
  diabetes
• Lactic acidosis in conditions in which there is
  a lack of oxygen in tissues.

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Compensatory Mechanism

• Metabolic acidosis
• Compensated by two mechanisms
• Hyperventilation
• Kidney ? production of HCO3

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Compensation in Metabolic Acidosis
Increased rate depth of respiration
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Mechanisms of Acid-Base Disturbances

• Respiratory acidosis
• Lungs are unable to excrete carbon dioxide
  effectively
• Respiratory infection in a patient with
  underlying chronic lung disease

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Compensatory Mechanism

• Respiratory Acidosis
• Compensated by the kidney ? production of HCO3

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Compensation in Respiratory Acidosis
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Mechanisms of Acid-Base Disturbances

• Metabolic alkalosis
• For example
• loss of gastric acid or its neutralization
• excess mineralocorticoids
• Results in hypoventilation and retention of C02
• There is no compensatory mechanism

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Mechanisms of Acid-Base Disturbances

• Respiratory alkalosis
• For example hyperventilation lowers PCO2
• Compensated by ? excretion of HCO3 by the kidneys

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Compensation in Respiratory Alkalosis
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Diagnostic Evaluation of Acid-Base Balance

• Clinical evaluation
• Laboratory studies
• pH
• PCO2
• Bicarbonate

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What did we learn today

• The body water compartments, and the associated
  electrolytes
• How the respiratory and renal systems participate
  in buffering of the bodies pH
• Respiratory acidosis/alkalosis and metabolic
  acidosis/alkalosis
• How the body compensates for pH imbalances