Electrolytes, Cations, and Anions Explained

• Electrolytes are salt substances forming ions in solution, conducting electricity, crucial for cell and organ function.
• Non-electrolytes, like glucose and urea, have no electrical charge.
• Cations are positive ions, while anions are negative ions.

Importance of Electrolytes

• Conducting nerve impulses.
• Muscle contraction.
• Hydration.
• Regulating acid-base balance (pH levels)

Composition of Electrolytes

• Electrolytes dissociate into ions in water, including inorganic salts, acids, bases, and proteins.
• Sodium is the major cation in extracellular fluid, with chloride as the major anion.
• Potassium is the major cation in intracellular fluid, with phosphate as the major anion.

Sodium Balance

• Sodium (Na+) is the most abundant cation in extracellular fluid (ECF).
• It maintains ECF osmotic balance.
• Normal serum concentration is 135-145 mmol/L.
• Pairs with chloride and bicarbonate to neutralize charge.
• Regulation occurs in the kidneys.
• Vital for water balance, nerve impulse conduction, and muscle contraction.
• The daily recommended sodium intake is about 2.3 grams per day.
• Sodium is excreted through sweat, urine, and feces.

Sodium Homeostasis

• Body mechanisms maintain normal sodium concentration in extracellular fluid.
• Homeostatic responses involve ADH control of water loss/retention by kidneys, thirst, and fluid exchange between ECF and ICF.

Sodium Imbalance

• Changes in Na+ affect blood pressure and volume.
• Imbalances include hyponatremia and hypernatremia.

Hyponatremia

• Low ECF Na+ concentration (below 135 mmol/L).
• Can come from water deficit or excessive salt intake.
• Clinical signs are thirst, sunken eyes, dry mouth and decreased urine output.
• Treatment:
  • Chronic: Sodium chloride 0.45%.
  • Acute: Intravenous 5% dextrose, corrected at 1 mEq per L per hour.

Hypernatremia

• High ECF Na+ concentration (above 145 mmol/L).
• Accompanied by hyperosomolarity (serum osmolarity higher than 300 mOsm/L).
• Commonly caused by dehydration.
• Etiology:
  • Water deficit.
  • Excess water loss: heat exposure, reduced water intake.
  • Reduced salt excretion.

Potassium Balance

• Potassium (K+) is the most abundant cation in intracellular fluid (ICF).
• Maintains osmotic-balance within ICF.
• Normal concentration: 3.5 to 5.5 mmol/L.
• Necessary for neuromuscular-control, acid-base balance, and intracellular-enzyme reactions.
• Disturbances can lead to hyperkalemia or hypokalemia.

Hyperkalemia

• Increased serum potassium level (above 5.5 mEq/L).
• Can be caused by:
  • High potassium intake.
  • Chronically low pH.
  • Decreased excretion (kidney failure, oliguria).
  • Shift of potassium from cells (burns, insulin-deficiency).
• Symptoms: Muscular spasm, including heart arrhythmias.

Hypokalemia

• Decreased serum potassium level (below 3.5 mEq/L).
• Can be caused by:
  • Decreased potassium intake.
  • Increased renal loss (diuretics).
  • Aldosteronism (excessive aldosterone secretion).
  • GIT loss (vomiting and diarrhea).
• Symptoms: Fatigue, muscular weakness, potentially lethal when affecting heart.

Calcium Balance

• Normal blood calcium: 2.2 to 2.6 mmol/L.
• Function:
  • Supporting material in bones as calcium phosphate.
  • Muscles contraction.
  • Act as cofactor in some coagulating cascades.
• Disturbances lead to hypocalcemia or hypercalcemia.

Hypocalcemia

• Decreased Serum Calcium Level.
• Causes:
  • Decreased intake or absorptions.
  • Increase loss.
  • Endocrine diseases.
• Symptoms:
  • Spasm of skeletal muscle.
  • Convulsions.
  • Arrhythmias.

Hypercalcemia

• Increased Serum Calcium Level.
• Causes:
  • Increased intake or absorption.
  • Endocrine disorder.
• Symptoms:
  • Constipation.
  • Frequent urination.
  • Coma and Renal Failure.

Acid-Base Balance

• pH measures acidity, and is the negative logarithm of hydrogen ions concentration.
• Normal systemic arterial pH is 7.35 to 7.45.
• Acid: Compound which disassociates to form hydrogen ions in solution.
• Base: Compound that combines hydrogen ions in the solution.

Acids

• Acids are proton (H+) donors.
• Hydrogen-containing substances dissociate in solution to release (H+).
• Physiologically important acids: carbonic acid (H2CO3), phosphoric acid (H3PO4), pyruvic acid (C3H4O3), lactic acid (C3H6O3).

Bases

• Bases are proton (H+) receptors.
• Molecules accept hydrogen ions (-OH).
• Physiologically important bases: bicarbonate (HCO3-), biphosphate (HPO4-2).

Acid-Base Imbalances

• Abnormality in pH control mechanisms can cause Acidosis or Alkalosis.
• Acidosis: Too much acid or too little base, frequently resulting in low blood PH.
• Alkalosis: Too much base or too little acid, frequently resulting in increased blood PH.
• Acid-base balance primarily concerns hydrogen (H+) and bicarbonate (HCO3-) ions.

Acidosis/Alkalosis

• pH changes affect cell-function, excitability of muscle and nerve cells, enzyme activity, and potassium level.

Acid-Base Regulation

• Extracellular fluid pH range is maintained by:
  • Chemical buffers: React rapidly (less than a second).
  • Respiratory regulation: React rapidly (seconds to minutes).
  • Renal regulation: React slowly (minutes to hours).

Chemical Buffer

• pH buffers in blood guard against sudden acidity changes, minimizing pH changes.
• Major ECF buffer is bicarbonate (H2CO3), with plasma protein, hemoglobin, and phosphate as other buffers.
• H+ + HCO3− → H2CO3 → H2O + CO2 (exhaled)
• The more hydrogen needed, the more bicarbonate is needed to maintain balance.

Respiratory Regulation

• Regulates acid-base balance by eliminating or retaining CO2, altering respiration depth/rate.
• Faster rate/more depth = raise ventilation eliminates more CO2 increases pH.
• Slower rate/less depth reduces ventilation retains CO2 lowers pH
• Increased breathing lowers blood carbon dioxide makes blood more basic.
• Decreased breathing increases blood carbon dioxide and makes blood more acidic.

Renal Regulation

• Kidneys regulate acid-base balance by controlling hydrogen ions (H⁺) excretion and bicarbonate (HCO₃⁻) reabsorption.
• Bicarbonate Reabsorption – The kidneys reabsorb nearly all filtered HCO₃⁻ in the proximal tubule, preventing loss of this key buffer.
• Hydrogen Ion Excretion – The kidneys excrete H⁺.
• Ammonium (NH₄⁺) Excretion – Glutamine metabolism generates NH₄⁺, which is excreted in urine.
• Titratable Acid Excretion – H⁺ is buffered by phosphate (HPO₄²⁻) in urine to form H₂PO₄⁻.
• New Bicarbonate Generation – The kidneys generate new HCO₃⁻ through NH₄⁺ excretion and titratable acid formation, helping to compensate for acid load.
• In Acidosis, the kidneys increase H⁺ excretion and HCO₃⁻ reabsorption.
• In Alkalosis, the kidneys reduce H⁺ excretion and increase HCO₃⁻ excretion.

Acid-Base Disorders

• Acid-base disorders are imbalances in the body's pH regulation, classified into four main types:

Metabolic Acidosis

• Cause: Loss of bicarbonate (HCO₃⁻) or accumulation of acids.
• Examples: Diabetic ketoacidosis, lactic acidosis, renal failure, diarrhea.
• Symptoms: Rapid-breathing, confusion, fatigue, hypotension, arrhythmias.

Metabolic Alkalosis

• Cause: Excess bicarbonate (HCO₃⁻) or loss of acid.
• Examples: Vomiting, diuretic use, hypokalemia.
• Symptoms: Muscle cramps, weakness, confusion, slow breathing, arrhythmias.

Respiratory Acidosis

• Cause: CO₂ retention from hypoventilation.
• Examples: COPD, respiratory depression, neuromuscular disorders.
• Symptoms: Headache, confusion, drowsiness, breathlessness, cyanosis.

Respiratory Alkalosis

• Cause: Excess CO₂ elimination from hyperventilation.
• Examples: Anxiety, fever, sepsis, high altitude.
• Symptoms: Dizziness, tingling, muscle spasms, confusion.