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Sodium Regulation and Cell Balance

  • Sodium Distribution: Sodium mostly outside cells in isotonic conditions, maintaining normal cell structure.

  • Hypotonic Solution: Lower sodium outside than inside, causing water to rush into the cell, leading to swelling and potential lysis (e.g., hemolysis of red blood cells).

  • Hypertonic Solution: Higher sodium outside than inside, causing cells to lose water, resulting in crenation (shrinkage).

Hormonal Regulation of Sodium

  • ADH (Antidiuretic Hormone): Increases water reabsorption, triggered by high plasma osmolality; inhibited during overhydration.

  • Renin-Angiotensin-Aldosterone System (RAAS): Regulates blood pressure and volume; renin production increases when sodium levels are low, leading to vasoconstriction and increased sodium (and water) reabsorption.

Hyponatremia

  • Definition: Low sodium concentration in blood.

  • Causes:

    • Depletional: Loss of sodium through vomiting, diuretics, poor intake.

    • Dilutional: Overhydration or inappropriate ADH secretion (SIADH).

  • Symptoms: Weakness, confusion, lethargy, neurologic impairment due to cellular swelling.

Hypernatremia

  • Definition: High sodium concentration in blood.

  • Causes: Loss of water more than sodium, excessive sodium intake, or low production of ADH (diabetes insipidus).

  • Symptoms: Thirst, confusion, muscle twitching, and seizures.

Potassium Regulation

  • Normal Range: 3.5 to 5.1 mmol/L; primarily intracellular cation.

  • Regulation: Controlled by diet and aldosterone; higher sodium leads to increased potassium excretion.

Hypokalemia

  • Definition: Low potassium levels.

  • Causes: Poor intake, diuretics, insulin therapy, excessive vomiting/diarrhea.

  • Symptoms: Muscle weakness, cramps, constipation, paralysis in severe cases.

Hyperkalemia

  • Definition: High potassium levels.

  • Causes: Excess intake, adrenal insufficiency, extensive tissue damage, renal failure.

  • Symptoms: Abnormal heart rhythms, potential cardiac arrest.

Chloride and Bicarbonate Regulation

  • Chloride: Follows sodium; maintains osmotic pressure, electrical neutrality. Regulation similar to sodium.

  • Bicarbonate: Functions in buffering blood pH; regulated by kidneys. Imbalances lead to metabolic acidosis or alkalosis.

Anion Gap Calculation

  • Definition: Estimates net unmeasured anions in serum; useful in diagnosing metabolic acidosis.

  • Calculation: Anion Gap = (Na⁺) - (Cl⁻ + HCO₃⁻).