Water & Electrolyte balance

• Hypotonic hydration


  Caused by cellular overhydration, or water intoxication. Osmolarity of fluid outside of cell decreases, causing hyponatremia (low Na+ outside of cells), resulting in movement of water into tissue cells and swelling of cells.
• Edema


  Atypical accumulation of fluid between cells, resulting in tissue swelling (not cell swelling). Can impair tissue function by reducing diffusion of oxygen and nutrients from blood into cells.
• Dehydration


  Water loss from cells and tissues due to: hemorrhage, severe burns, excessive vomiting/diarrhea, profuse sweating, water deprivation, diuretic abuse, or endocrine disturbances. Cells shrink ("crenate") as a result of water loss.
• Nonelectrolytes


  Most are organic molecules (glucose, lipids, creatinine, and urea); Not charged when placed in water.
• Electrolytes


  Inorganic salts, all acids and bases, and some proteins; Result in charge molecules when placed in water.
• Sodium


  The major extracellular cation. Aldosterone (part of the RAAS) plays biggest role in regulation of Na+ by kidneys.
• Sodium reabsorption


  65% reabsorbed in PCT, 25% reclaimed in Nephron Loop, and 10% reabsorbed by DCT and CD.
• Hyponatremia


  Caused by: excessive water loss (due to excessive vomiting/diarrhea, burns, diuretics) or Addison's Disease, Kidney Disease, or water intoxication; Results in: confusion, coma, convulsions, and low blood volume/pressure is possible.
• Hypernatremia


  Caused by: dehydration (elderly or infants) or excess NaCl in IV; Results in: thirst, confusion, lethargy, coma, and convulsions.
• Potassium


  The major intracellular cation. Aldosterone stimulates the secretion of K+ from the DCT and CD. Affects resting membrane potential (RMP) in neurons and muscle cells (especially cardiac muscle).
• Hypokalemia


  Decreases in extracellular K+ cause hyperpolarization and nonresponsiveness. Caused by: Vomiting, Diarrhea, Cushing's Syndrome, Starvation, and Diuretics. Symptoms: Cardiac Arrhythmias, Weakness, Confusion, Nausea, Vomiting.
• Hyperkalemia


  Increases in extracellular K+ cause decreased RMP, causing depolarization, followed by reduced excitability. Caused by: Renal Failure, Aldosterone Deficiency, IV injection of excessive KCl, burns/tissue damage. Symptoms: Vomiting, Diarrhea, Nausea, Cardiac Arrhythmias, Paralysis, Death.
• Normal blood pH

  7.35-7.45. Arterial blood pH = 7.4, Venous blood pH = 7.35.

  
• Alkalosis


  Arterial blood pH rises above 7.45, resulting in Alkalemia.
• Acidosis


  Arterial pH drops below 7.35.
• Hypokalemia


  Decreased extracellular K+ causing hyperpolarization and nonresponsiveness
• Causes of hypokalemia


  • Vomiting
  • Diarrhea
  • Cushing's Syndrome
  • Starvation
  • Diuretics
• Symptoms of hypokalemia


  • Cardiac Arrhythmias
  • Weakness
  • Confusion
  • Nausea
  • Vomiting
• Hyperkalemia


  Increases in extracellular K+ causing decreased RMP, depolarization, and reduced excitability
• Causes of hyperkalemia


  • Renal Failure
  • Aldosterone Deficiency
  • IV injection of excessive KCl
  • Burns/tissue damage
• Symptoms of hyperkalemia


  • Vomiting
  • Diarrhea
  • Nausea
  • Cardiac Arrhythmias
  • Paralysis
  • Death
• Normal blood pH = 7.35-7.45

  
• Arterial blood pH = 7.4
• Venous blood pH = 7.35

  
• Alkalosis

  Arterial blood pH rises above 7.45 resulting in Alkalemia

  
• Acidosis

  Arterial pH drops below 7.35 resulting in Acidemia
• pH scale


  0-14, neutral at 7, acidic 0-7, basic 7-14
• Hydrogen Ion Regulation


  • Chemical buffer systems
  • Respiratory system
  • Renal (urinary) system
• Chemical buffers


  Act within seconds, can act as an acid or a base
• As more CO2 accumulates

  H+ ions increase, resulting in Acidosis
• Compensating for Acidosis


  Respiratory rate and depth are increased to eliminate more CO2 and lower H+ ions and raise blood pH
• Compensating for Alkalosis


  Respiratory rate and depth are decreased to accumulate more CO2 and raise H+ ions and lower blood pH
• Chemical buffers cannot eliminate excess acids or bases from the body
• The lungs can eliminate carbonic acid by eliminating carbon dioxide
• Only the kidneys can rid the body of hydrogen ions as well as metabolic acids
• Compensating for Acidosis (kidneys)

  Reabsorb more HCO3- ions and secrete more H+ ions to lower H+ and increase pH
• Compensating for Alkalosis (kidneys)

  Reabsorb more H+ ions and secrete more HCO3- ions to increase H+ and lower pH
• Respiratory Acidosis

  Blood pH is below 7.35 (PCO2 > 45 mm Hg) due to decreased CO2 elimination (hypoventilation)
• Respiratory Alkalosis

  Blood pH is above 7.45 (PCO2 < 35 mm Hg) due to increased CO2 elimination (hyperventilation)
• Metabolic Acidosis

  Blood pH is below 7.35 due to increased bicarbonate loss or increased acid accumulation