Fluid, Electrolyte, AcidBase Balance

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Fluid, Electrolyte, Acid-Base Balance
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Introduction

• Most human weight is water.
• 99 of the volume outside the cell is water.
• Water is an essential ingredient of cytoplasm.
• If water content of the body changes, cellular
  activities are jeopardized.
• We must maintain a normal volume and composition
  in the extracellular fluid (ECF) and the
  intracellular fluid (ICF, known as cytosol).

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• High calcium or potassium ions in the ECF can
  cause cardiac arrhythmias.
• Low pH can cause breakdowns in chemical bonds,
  change the shape of complex molecules, disrupt
  cell membranes and impair tissue functions.
• It is very important to have correct water
  balance to keep these ions saturated so the body
  chemistry can function correctly.

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The ICF and ECF are called fluid compartments
because they behave as distinct entities.
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Principal ions in the ECF (interstitial) are
sodium, chloride and bicarbonate. ICF
(intracellular) contains an abundance of
potassium, magnesium, phosphate ions, and
negatively charged proteins.
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Fluid Balance

• Water circulates freely within the ECF
  compartment.
• Capillary blood pressure forces water out of the
  plasma and into the interstitial spaces.
• Some water is reabsorbed along the distal portion
  of the capillary bed and the lymphatic vessels
  for transport to the venous circulation.

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• Water moves back and forth the epithelial
  surfaces lining the peritoneal, pleural,
  pericardial cavities and synovial membranes
  lining joint capsules.
• Flow rate is significant 7 liters of peritoneal
  fluid is produced and reabsorbed each day.
• Roughly 2500 ml of water is lost through urine,
  feces, and perspiration.
• Depending on the activities additional deficits
  can reach well over 4 liters an hour.
• Losses can be balanced through eating (48),
  drinking (40) and metabolic generation (12).

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Fluid Shifts

• Water movement between ECF and ICF is called
  fluid shift.
• shifts occur in response to changes in the
  osmotic concentration, or osmolarity, of the
  extracellular fluid.

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If the ECF becomes more concentrated with respect
to the ICF, water will move from the cells into
the ECF until osmotic equilibrium is restored.
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If the ECF becomes hypotonic with respect to the
ICF water will move from the ECF into the cells,
and the volume of the ICF will increase
accordingly
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Electrolyte Balance

• An individual is in balance when the rates of
  gain and loss are equal for each of the
  individual electrolytes in the body.
• Electrolyte balance is important because 1) a
  gain or loss of electrolytes can cause a gain or
  loss in water. 2) the concentrations of
  individual electrolytes affect a variety of cell
  functions.
• Sodium and potassium deserve close attention
  because they are major contributors to the
  osmotic concentrations of the ECF and ICF and
  they have direct effects on the normal
  functioning of living cells.

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• Sodium is the dominant cation in the ECF.
• Potassium is the dominant cation in the ICF.
• Most common problems with electrolyte balance are
  caused by an imbalance between sodium gains and
  losses.
• Problems with potassium balance are less common
  but significantly more dangerous than those
  related to sodium balance.

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Sodium Balance

• The rate of sodium uptake across the digestive
  epithelium is directly related to the amount of
  sodium in the diet.
• Losses occur mainly in the urine and through
  perspiration.
• Rate of sodium reabsorption along the DCT is
  regulated by aldosterone levels.
• Aldosterone stimulates sodium ion reabsorption.

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Potassium Balance

• Potassium ion concentrations in the ECF are very
  low.
• Potassium excretion increases 1) when sodium ion
  concentrations decline. 2) As ECF potassium
  concentrations rise.
• The rate of potassium excretion is regulated by
  aldosterone aldosterone stimulates potassium ion
  excretion.

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Acid-Base Balance

• pH of normal body fluids ranges form 7.35-7.45
  variations outside this range produce acidosis or
  alkalosis.
• Carbonic acid is the most important factor
  affecting the pH of the ECF.
• In solution CO2 reacts with water to form
  carbonic acid the dissociation of carbonic acid
  releases hydrogen ions.
• Organic or metabolic acids include products of
  metabolism such as lactic acid and ketone bodies.

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Buffers Buffer Systems

• Buffers are dissolved compounds that can provide
  or remove hydrogen ions and thereby stabilize the
  pH of a solution.
• Buffers include weak acids that can donate
  hydrogen ions and weak bases that can absorb
  them.
• Three major buffer systems protein buffer
  systems in the ECF and ICF, the carbonic
  acid-bicarbonate buffer system, most important in
  the ECF and the phosphate buffer system in the
  ICF.

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Buffer Systems

• Protein buffer systems component amino acids
  respond to changes in H concentrations. Blood
  plasma proteins and hemoglobin in RBCs help
  prevent drastic changes in pH.
• Carbonic acid-bicarbonate buffer system- prevents
  pH changes due to organic acids in the ECF.
• Phosphate buffer system important in preventing
  pH changes in the intracellular fluid.

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Respiratory Acidosis

• Respiratory system is unable to eliminate all of
  the CO2 generated by peripheral tissues.
• Primary symptom is low plasma pH due to
  hypercapnia, an elevated plasma Pco2
• Usual cause is hypoventilation, abnormally low
  respiratory rate.

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Respiratory Alkalosis

• Problems with this are relatively uncommon.
• Develops when respiratory activity lowers plasma
  Pco2 to below normal levels, called hypocapnia.
• Temporary hypocapnia can be produced by
  hyperventilation.
• Condition seldom persists long enough to cause a
  clinical emergency.

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Metabolic Acidosis

• Second most common type of acid-base imbalance.
• Most fre quent cause is the production of a large
  number of metabolic acids such as lactic acid or
  ketone bodies.
• Can be caused by the inability to excrete
  hydrogen ions from the kidneys and any condition
  causing severe kidney damage.

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Metabolic Alkalosis

• Occurs when bicarbonate ion concentrations become
  elevated.
• Bicarbonate ions interact with hydrogen ions in
  solution to form carbonic acid and the reduction
  of H ions causes symptoms of alkalosis.
• Cases of severe metabolic alkalosis are
  relatively rare.