Electrolytes

• Functions of Electrolytes

  1. Volume and osmotic pressure regulation: Sodium, Chloride, Potassium

  2. Myocardial rhythm and contractility: Potassium, Calcium, Magnesium

  3. Neuromuscular excitability: Potassium, Calcium, Magnesium

  4. Cofactors in enzyme activation: Magnesium, Calcium, Zinc, Chloride

  5. Regulation of ATPase ion pumps: Magnesium

  6. Acid-base balance: Bicarbonate, Potassium, Chloride

  7. Production and use of ATP from glucose: Magnesium, Phosphate
• Anion


  • Ions that carry negative (-) charge
  • In electrophoresis, anions move toward the anode
  • E.g.: Chloride, Bicarbonate, Phosphate
• Factors that influence concentration or level of electrolytes in the plasma

  • Dietary intake: Majority of electrolytes come from the diet
  • Functions of the organs in the body: GIT, Kidneys, Skin
• Cations

  • Ions that carry positive (+) charge
  • In electrophoresis, cations move toward the cathode
  • E.g.: Sodium, Potassium, Calcium, Magnesium
• Classifications of Electrolytes - According to the charge it carries

  • Anion
  • Cations
• Functions of the organs in the body

  1. GIT: Absorption of electrolytes from the diet

  2. Kidneys: Excretion or reabsorption of electrolytes

  3. Skin: Removal of excess electrolytes through perspiration
• Extracellular electrolytes

  • Extracellular intravascular: located in the plasma
  • Extracellular extravascular: located in the interstitial fluid
  • E.g.: Sodium, Chloride, Bicarbonate
• Gatorade is encouraged for people who are athletes or have diarrhea to replace rapid loss of electrolytes
• Electrolytes

  Ions capable of carrying an electric charge (can be a positive or negative charge)
• Intracellular

  • Inside or within the cell
  • E.g.: Potassium, Phosphate
• Osmolality

  • Physical property of a solution based on concentration of solutes per kilogram of solvent
  • Direct reflection of solute concentration in solvent
  • Increased blood osmolality indicates concentrated plasma, while low blood osmolality indicates diluted plasma
• Location of Water in the body

  • Intracellular Fluid (ICF): ⅔ of Body Water
  • Extracellular Fluid (ECF): ⅓ of Body Water
  • Extracellular, Intravascular: Plasma
  • Extracellular, Extravascular: Interstitial Fluid
• Skin

  1. Through the perspiration process, excess electrolytes can be removed through the skin

  2. White map-like stains on black shirts after perspiration are electrolytes or salts excreted by the skin
• Passive Transport

  1. Passive movement of ions across a membrane

  2. No energy (ATP) required

  3. Movement of ions based on concentration gradient to achieve homeostasis
• Thirst sensation is activated when plasma osmolality is increased, preventing dehydration by stimulating water intake
• Hormones

  1. Hormones can regulate or control the concentration of electrolytes

  2. Aldosterone regulates the reabsorption of sodium in exchange for potassium in the kidneys

  3. Sodium is saved by aldosterone in the kidneys then potassium is excreted, Activity of aldosterone is always opposite to the sodium and potassium
• Active Transport

  1. Mechanism requiring energy (ATP) to move ions across cellular membranes

  2. Example: ATPase-Dependent Ion Pumps

  3. Sodium-Potassium ATPase Ion Pump maintains balance of charge in and out of the cell
• Arginine Vasopressin Hormone (AVP) is responsible for water retention and increased water reabsorption in the kidneys, activated when plasma osmolality is decreased
• Water

  • 40-75% of body weight
  • Electrolytes are present in body fluids, water helps maintain electrolytes
  • Water is the universal solvent
  • Water is essential for biochemical processes
  • Water sustains life
• Water

  1. Transport nutrients to cells

  2. Determines cell volume

  3. Removes waste products through urination/perspiration

  4. Acts as the body's coolant by removing excess heat and lowering body temperature
• Distribution of Body Water in Adult

  • Extracellular: Plasma (5% of body weight, 8% of total body water), Interstitial (15% of body weight, 25% of total body water), Intracellular (40% of body weight, 67% of total body water)
• Kidneys

  1. Electrolytes can be excreted or reabsorbed in the kidneys

  2. Excess electrolytes can be removed, and the needed electrolytes can be conserved or reabsorbed in the kidneys or nephrons
• Other Factors

  1. Atrial Natriuretic Peptide (ANP) promotes sodium excretion in kidneys and is opposite to aldosterone

  2. Arginine Vasopressin Hormone (AVP) promotes increased water reabsorption in kidneys

  3. Glomerular Filtration Rate (GFR) is increased with volume expansion in the blood
• Arginine Vasopressin Hormone (AVP)

  1. Responsible for water retention and increased water reabsorption in the kidneys

  2. Activated when plasma osmolality is decreased or with excess water load

  3. Suppressed in excess water load resulting in diuresis

  4. Activated in water deficit
• Electrolytes

  1. Increased plasma sodium level increases urinary sodium excretion

  2. Excessive sodium must be excreted to maintain a balance of sodium concentration
• Substances that can Suppress AVP/AVH Secretion

  • Alcohol (ethanol)
  • Caffeinated drinks (coffee, tea)
  • Soda, etc.
• Determination Of Osmolality And Osmolal Gap

  1. Measurement of serum or urine osmolality indicates the number of molecules per kilogram solvent

  2. Effects of substances dissolved in the solvent on colligative properties of the solution: freezing point, vapor pressure, osmotic pressure

  3. Osmolality in electrolytes is studied because electrolytes are major contributors to plasma osmolality
• Regulation of Blood Volume

  1. Renin-Angiotensin-Aldosterone System is activated when there is low plasma-sodium content, low blood pressure, or low blood volume

  2. Renin acts on angiotensinogen to form Angiotensin I, which is converted to Angiotensin II by Angiotensin Converting Enzyme (ACE)

  3. Angiotensin II promotes vasoconstriction of renal arterioles, stimulates sodium reabsorption in the Proximal Convoluted Tubule (PCT), and stimulates adrenal cortex to release aldosterone

  4. These actions correct renal blood flow and increase blood volume back to normal
• Usual ER Tests include Sodium, Potassium, Creatinine, CBC
• Sodium

  • Important in maintaining blood volume and osmotic regulation
  • Low plasma concentration of sodium concentration could activate Renin Angiotensin Aldosterone System (RAAS)
• Causes of Hyponatremia include Increased Sodium Loss and Increased Water Retention
• Blood volume status affects sodium excretion through

  • Aldosterone - promotes increased renal reabsorption of sodium
  • Angiotensin II - Stimulates the adrenal cortex to produce more aldosterone
  • Atrial Natriuretic Peptide (ANP) promotes increased excretion of sodium
• Major contributors of plasma osmolality

  • Glucose
  • Urea (Major NPN in plasma)
  • Sodium (major Cation in plasma)
  • Chloride (major Anion in plasma)
• Osmolality in Electrolytes

  Electrolytes are some of the major contributors of plasma osmolality
• Concentration of Cations and Anions in Extracellular and Intracellular Water

  • Na+: 136 - 145 (Extracellular), 15 (Intracellular)
  • K+: 3.5 - 5.1 (Extracellular), 150 (Intracellular)
  • Cl-: 98 - 107 (Extracellular), 1 (Intracellular)
  • Ca2+: 2.15 - 2.5 (Extracellular), 1 (Intracellular)
  • HCO3-: 23 - 29 (Extracellular), 10 (Intracellular)
  • HPO42-: 0.78 - 1.42 (Extracellular), 50 (Intracellular)
  • Mg2+: 0.63-1 (Extracellular), 13.5 (Intracellular)
  • SO42-: 0.5 (Extracellular), 10 (Intracellular)
• Reference Values for Sodium are 135 to 145 mmol/L
• Sodium-Potassium-ATPase Ion Pump

  1. Regulates the sodium concentration in the plasma and in the cell through active transport

  2. Moves 3 Na+ ions out of the cell in exchange for 2 K+ that will enter the cell
• Clinically Significant Electrolytes

  • Sodium
  • Potassium
  • Chloride
  • Calcium
  • Hydrogen Phosphate Ion
  • Magnesium
  • Sulfate
• Plasma concentration depends on renal regulation

  • Through intake of water (in response to thirst) sodium levels can be corrected
  • Excretion of water as affected by AVP/ADH: Increased water reabsorption
• Threshold Critical Value for Sodium: Hypernatremia - 160 mmol/L above, Hyponatremia - 120 mmol/L below