Lecture Notes: Electrolytes

Key Functions of Electrolytes

• Control osmosis of water
• Maintain acid-base balance
• Carry electrical current necessary for:
  • Action potentials
  • Graded potentials
  • Hormone secretion
  • Neurotransmitter activity
• Act as co-factors for enzymes

Measurement and Distribution

• Expressed in milliequivalents per liter
• Present in plasma, interstitial fluid, and intracellular fluid
• Plasma contains more proteins (negative charge) impacting osmotic pressure

Electrolyte Distribution

• Sodium (Na+):
  • Major extracellular cation
  • Found mainly in plasma and interstitial fluid
• Potassium (K+):
  • Major intracellular cation
  • Important for fluid volume, impulse conduction, and muscle contraction
• Calcium (Ca2+):
  • Found more in blood; important for bones, teeth, blood clotting, neurotransmission
• Magnesium (Mg2+):
  • Intracellular; enzyme co-factor, neuromuscular activity
• Chloride (Cl-):
  • Major extracellular anion
  • Moves with sodium; important for hydrochloric acid in the stomach
• Bicarbonate (HCO3-):
  • Prominent in plasma; major part of acid-base buffer system
• Phosphate (PO4):
  • Intracellular; part of ATP, DNA, RNA, acts as buffer

Regulatory Mechanisms

• Sodium
  • Regulated by aldosterone, ADH, and atrial natriuretic peptide
  • Imbalance can lead to edema or hypovolemia
• Chloride
  • Follows sodium; aids in forming hydrochloric acid
• Potassium
  • Controlled by aldosterone; crucial for membrane potentials
• Bicarbonate
  • Regulated by kidneys, acting as buffer
• Calcium
  • Regulated by parathyroid hormone and calcitriol
• Magnesium
  • Influenced by various factors including hormone levels
• Phosphate
  • Regulated alongside calcium; critical in bone metabolism

Electrolyte Imbalances and Risks

• Edema: Excess sodium leads to water retention
• Hypovolemia: Excess sodium loss results in low blood volume
• High-Risk Groups:
  • Elderly, especially in care homes
  • Children
  • Post-surgery patients
  • Those with chronic diseases or altered consciousness

Lecture Goals

• Understand what electrolytes are
• Learn units of measurement for electrolytes
• Identify the importance and distribution of key electrolytes (sodium, chloride, potassium, bicarbonate, calcium, magnesium, phosphate)
• Relate electrolyte balance to conditions like edema and hypovolemia
• Recognize individuals most at risk for fluid and electrolyte imbalances