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

This quiz covers the role of metals such as sodium, potassium, magnesium, and calcium in human physiology and their relation to diseases. Learn about the physiological functions and associated diseases of these metals.