Metals in Physiology and Pathology

Sodium

• Mostly found in blood and extracellular fluid (ECF)
• Excreted mainly in urine
• Physiological functions:
  • Maintains normal cellular homeostasis
  • Regulates fluid and electrolyte balance and blood pressure
  • Main regulator of ECF volume through its osmotic action
  • Transports nutrients and substrates through plasma membranes
  • Important for the excitability of muscle and nerve cells
• Sodium-associated diseases:
  • Hyponatremia (serum Na < 135 mmol/L): water leaves blood and enters cells, causing cell swelling
  • Hypernatremia (serum Na > 145 mmol/L): decrease in total body water relative to electrolytes, causing water to leave cells and enter blood
  • Excessive sodium intake: facial puffiness, high blood pressure, heart disease, and stroke

Potassium

• Mostly found inside cells, present in all body tissues
• Excreted mainly in urine, with some in sweat and stool
• Strong relationship with sodium
• Physiological functions:
  • Essential for normal cell function
  • Maintains intracellular fluid volume and transmembrane electrochemical gradients
  • Helps preserve acid-base balance and maintain isotonicity and electrodynamic cellular function
  • Activates many enzymes, e.g., pyruvate kinase
  • Essential for transmission of nerve impulses, contraction of cardiac muscles, skeletal and smooth muscles, tissue synthesis, gastric secretion, and renal function
  • Relaxes walls of blood vessels, lowering blood pressure
• Diseases associated with potassium:
  • Hypokalemia (< 3 mmol/L): low levels of K in blood, caused by excessive K loss in urine or low K intake
  • Hyperkalemia (> 6.0 mmol/L): high levels of K in blood, can be life-threatening, causing heart muscle activity reduction, weakness, and paralysis

Magnesium

• 50% of body's magnesium is in bone, with very little in blood
• Physiological functions:
  • Cofactor in various structures/enzymes that regulate reactions
  • Protein synthesis, muscle and nerve function, blood pressure regulation
  • Required for energy production, oxidative phosphorylation, and glycolysis
  • Regulates insulin secretion in pancreatic beta cells
  • Critical for phosphorylation of insulin receptor
  • Contributes to formation (structural development) of bone and teeth
• Diseases associated with magnesium:
  • Hypomagnesemia: too low levels of magnesium in blood