Lecture Notes: Electrolytes

Introduction to Electrolytes

• Electrolytes have four basic functions in the body:
  • Control osmosis of water
  • Maintain acid-base balances
  • Carry electrical currents for action potentials, graded potentials, hormone secretion, neurotransmitter function
  • Act as co-factors for enzymes
• Concentration expressed in milliequivalents per liter for plasma, interstitial fluid, intracellular fluid

Differences in Plasma and Interstitial Fluid

• Plasma contains proteins aiding in blood colloid osmotic pressure (negative charge)
• Plasma has more sodium, less chloride compared to interstitial fluid
• Interstitial fluid lacks plasma proteins due to being unable to move out of blood vessels

Electrolyte Distribution in Fluid Compartments

• Sodium: Abundant in interstitial fluid and plasma, little inside cells
• Potassium: Mainly inside cells
• Calcium: Mainly in blood, low concentration overall
• Magnesium: Primarily intracellular
• Chloride: Follows sodium, more in interstitial fluid
• Bicarbonate: Mostly in interstitium and plasma
• Phosphate: Mainly inside cells
• Sulfates: Components of proteins, involved in strong disulfide bonds
• Protein Anions: More inside cells, plasma proteins present

Detailed Analysis of Key Electrolytes

Sodium (Na+)

• Most abundant extracellular cation
• Accounts for half of the osmolarity of extracellular fluid
• Daily intake usually exceeds requirements
• Regulated by aldosterone and atrial natriuretic peptide
• Excess sodium can cause edema, loss can cause hypovolemia

Chloride (Cl-)

• Major extracellular anion
• Moves easily between compartments
• Indirectly controlled by aldosterone and ADH
• Important for forming hydrochloric acid in the stomach

Potassium (K+)

• Most abundant intracellular cation
• Maintains fluid volume, muscle function, and pH regulation
• Plasma level controlled by aldosterone
• Affects heart and muscle function

Bicarbonate (HCO3-)

• Prominent plasma anion, part of acid-base buffer system
• Increased in systemic capillaries, decreased in pulmonary capillaries
• Regulated by kidneys through intercalated cells

Calcium (Ca2+)

• Most abundant ion in the body, mainly extracellular
• Important for bones, teeth, muscle function, neurotransmitter release
• Regulated by parathyroid hormone and calcitriol

Magnesium (Mg2+)

• Primarily intracellular
• Co-factor for enzyme systems, involved in neural transmission and myocardial functioning
• Regulated by several factors, including calcium and extracellular fluid volume

Phosphate (PO4^3-)

• Present in bones, teeth, ATP, DNA, RNA
• Acts as a buffer for hydrogen ions
• Regulated by parathyroid hormone and calcitriol

Electrolyte Imbalance and Risk Factors

• Electrolyte balance relates to conditions like edema and hypovolemia
• At-risk individuals:
  • Dependent individuals (elderly, those with dementia)
  • Children
  • Those undergoing medical treatment with IVs, catheters
  • Post-operative patients
  • Burn victims
  • Those with chronic diseases or altered states of consciousness

Lecture Goals

• Define what an electrolyte is
• Describe the unit of measurement for electrolytes
• List the concentration locations of key electrolytes
• Explain how electrolyte balance is related to edema and hypovolemia
• Identify individuals at risk for fluid and electrolyte imbalances