Major Intracellular and Extracellular Ions

Body Water Distribution

• The human body consists of approximately 70% water.

  • Intracellular Fluid (ICF): fluid inside the cells, approximately 2/3 of total body water.

  • Extracellular Fluid (ECF): fluid outside cells, includes interstitial fluid, blood plasma, and lymph.

    • Interstitial fluid (ISF): 25% of body water.

    • Plasma: 5-8% of body water (Intravascular Fluid - IVF).

    • Transcellular fluids: 1-2% (includes CSF, intraocular fluids, serous membranes, GIT, respiratory, and urinary tracts).

Electrolytes

• Electrolytes are substances that, when dissolved, separate into ions and can carry an electrical current.

  • Cations: positively charged electrolytes (e.g., K+, Na+).

  • Anions: negatively charged electrolytes (e.g., Cl-, HCO3-).

• Intracellular Electrolytes: Potassium (K+), Magnesium (Mg2+), Phosphorus (P).

• Extracellular Electrolytes: Sodium (Na+), Chloride (Cl-), Bicarbonate (HCO3-).

• Differences in ion concentrations across cell membranes result from metabolic activity.

  • K+ levels determine ICF volume, while Na+ levels determine ECF volume.

  • Electrolyte disturbances often involve the interrelation of positively and negatively charged ions.

Compartmentalization of Total Body Water

• In an average 70 kg man:

  • Total Body Water: 42 liters.

    • Intracellular Fluid: 28 liters.

    • Extracellular Fluid: 14 liters.

      • Interstitial Fluid: 9.5 liters.

      • Plasma: 3.5 liters.

      • Transcellular Fluid: 1 liter.

Disturbances of Water Balance

1. Dehydration:

   • Most common; caused by inadequate water intake, diarrhea, or vomiting.

   • Can lead to excessive water loss, especially in comatose or debilitated patients.

2. Over-hydration:

   • Less common; occurs with excessive fluid intake when renal function is impaired.

   • Conditions causing water imbalance also disrupt electrolyte composition.

3. Depletion of Electrolytes:

   • Causes include vomiting/diarrhea (Na+ and K+ loss), diuretics, and renal tubular disease.

Key Electrolytes

1. Sodium (Na+):

   • Most abundant electrolyte; crucial for osmotic pressure and functions in heart and cell membranes.

   • Normal range: 135-145 mEq/L.

2. Potassium (K+):

   • Essential for nerve impulse conduction and muscle contractions.

   • Normal range: 3.5-5.3 mEq/L; critical levels: below 2.5 or above 7.0 can result in cardiac arrest.

3. Chloride (Cl-):

   • Regulates osmotic pressure and acid-base balance.

4. Calcium (Ca2+):

   • Primarily in bones; essential for muscle contractions and nerve impulse transmission.

   • Plays a role in blood coagulation and maintaining cell membrane integrity.

5. Magnesium (Mg2+):

   • Important for metabolism and energy storage; critical for heart and muscle function.

Sodium/Chloride Imbalance

• Regulated by kidneys; influenced by aldosterone.

  • Na+ is responsible for water retention; Cl- works in tandem with Na+.

• Normal Chloride range: 95-108 mEq/L.

Functions of Electrolytes

• Chloride:

  • Maintains serum osmolarity; assists in acid/base balance.

  • Decreased levels often due to gastrointestinal losses.

• Sodium:

  • Key for nerve impulse transmission; regulates vascular fluid osmolarity.

  • Sodium/potassium pump vital for acid-base homeostasis.

Hyponatremia

• Excessive sodium loss or water gain; common causes:

  • Diuretic therapy, excessive sweating, insufficient Na intake, GI losses, and hypotonic fluid administration.

• Symptoms include headache, confusion, muscle cramps, and convulsions.

Treatment for Hyponatremia

• Monitor symptoms; restrict fluids, monitor serum Na levels.

• Administer IV normal saline or lactated ringers as needed.

Hypernatremia

• Occurs with excessive water loss or sodium retention.

• Causes include vomiting, diarrhea, inadequate antidiuretic hormone (ADH) levels, certain medications, and burns.

• Symptoms include thirst, flushed skin, low urinary output, tachycardia, and seizures.

Treatment for Hypernatremia

• Implement a low sodium diet; encourage fluid intake.

• Monitor blood pressure and heart rate, especially in hypovolemic patients.

Potassium

• Most abundant intracellular cation (97% in ICF); normal K+ levels crucial for muscle and nerve function.

Hypokalemia

• Causes include prolonged diuretic therapy, inadequate intake, and excessive insulin.

• Symptoms: fatigue, muscle weakness, hypotension, and cardiac dysrhythmias.

Hyperkalemia

• Higher than normal K+ levels, can result from renal dysfunction; may cause decreased heart rate and muscle weakness.

Calcium

• 99% found in bones; critical for muscle contraction, nerve impulse, and blood clotting.

Hypercalcemia

• Signs include muscle weakness, nausea, extreme thirst, and possible cardiac arrest.

Hypocalcemia

• Reduced calcium levels increase the excitability of nerves and muscles.

Chloride

• Main extracellular anion; regulates hydration and osmotic pressure.

Hypochloremia

• Decreased chloride; can result from tubular reabsorption issues or metabolic acidosis.

Hyperchloremia

• Increased chloride levels; may result from dehydration or excessive chloride intake.

Phosphate

• Principal anion of ICF; important for calcium metabolism and bone health.

Bicarbonate

• Second most prevalent anion in ECF; vital for acid-base balance.