Physiology

Electrolyte balance is critical for maintaining cellular function, fluid balance, and overall health. Deviations from normal electrolyte levels can indicate various underlying conditions

Normal States

Normal Electrolyte Concentrations
- Electrolyte concentrations are maintained within narrow physiological ranges
- Sodium (\(Na^+\)): 136-145 mmol/L (conventional and SI units)
- Potassium (\(K^+\)): 3.5-5.1 mmol/L (conventional and SI units)
- Chloride (\(Cl^-\)): 98-107 mmol/L (conventional and SI units)
- Bicarbonate (\(HCO_3^-\)): 23-29 mmol/L (conventional and SI units)
- Calcium (\(Ca^{2+}\)): 8.6-10.2 mg/dL or 2.2-2.6 mmol/L (SI units)
- Magnesium (\(Mg^{2+}\)): 1.7-2.2 mg/dL or 0.70-0.90 mmol/L (SI units)
- Phosphorus (\(P\)): 2.5-4.5 mg/dL or 0.81-1.45 mmol/L (SI units)
Electrolyte Distribution
- Appropriate distribution of electrolytes between intracellular fluid (ICF) and extracellular fluid (ECF)
- Sodium: Predominantly extracellular
- Potassium: Predominantly intracellular
Hormonal Regulation
- Aldosterone: Regulates sodium and potassium balance
- Antidiuretic Hormone (ADH): Regulates water balance, affecting sodium concentration
- Parathyroid Hormone (PTH): Regulates calcium and phosphate balance
- Vitamin D: Regulates calcium absorption and bone metabolism
Kidney Function
- Normal kidney function is essential for maintaining electrolyte balance through reabsorption and excretion

Abnormal States

Sodium Imbalances * Hyponatremia * Hypernatremia
Potassium Imbalances * Hypokalemia * Hyperkalemia
Chloride Imbalances * Hypochloremia * Hyperchloremia
Calcium Imbalances * Hypocalcemia * Hypercalcemia
Magnesium Imbalances * Hypomagnesemia * Hypermagnesemia
Phosphate Imbalances * Hypophosphatemia * Hyperphosphatemia

Sodium Imbalances

Hyponatremia
- Definition: Serum sodium concentration < 136 mmol/L
- Causes
  - Hypovolemic Hyponatremia: Sodium loss with greater water loss (e.g., vomiting, diarrhea, diuretics)
  - Euvolemic Hyponatremia: Normal sodium levels, but increased water retention (e.g., SIADH, hypothyroidism)
  - Hypervolemic Hyponatremia: Increased sodium and water retention, with water excess being greater (e.g., heart failure, cirrhosis)
- Symptoms: Nausea, headache, confusion, muscle cramps, seizures, coma
Hypernatremia
- Definition: Serum sodium concentration > 145 mmol/L
- Causes
  - Hypovolemic Hypernatremia: Water loss with greater sodium loss (e.g., sweating, diarrhea)
  - Euvolemic Hypernatremia: Water loss with normal sodium levels (e.g., diabetes insipidus)
  - Hypervolemic Hypernatremia: Sodium gain with greater water gain (e.g., hypertonic saline administration)
- Symptoms: Thirst, confusion, muscle twitching, seizures, coma

Potassium Imbalances

Hypokalemia
- Definition: Serum potassium concentration < 3.5 mmol/L
- Causes
  - Decreased Intake: Poor dietary intake
  - Increased Loss: Vomiting, diarrhea, diuretics, hyperaldosteronism
  - Cellular Shift: Insulin, alkalosis, beta-adrenergic agonists
- Symptoms: Muscle weakness, fatigue, cardiac arrhythmias, constipation
Hyperkalemia
- Definition: Serum potassium concentration > 5.1 mmol/L
- Causes
  - Decreased Excretion: Kidney failure, hypoaldosteronism, potassium-sparing diuretics
  - Cellular Release: Tissue damage, hemolysis, acidosis, insulin deficiency
  - Increased Intake: Excessive potassium supplementation
- Symptoms: Muscle weakness, cardiac arrhythmias, paralysis, cardiac arrest

Chloride Imbalances

Hypochloremia
- Definition: Serum chloride concentration < 98 mmol/L
- Causes
  - Loss of Chloride: Vomiting, nasogastric suctioning, diuretics
  - Increased Bicarbonate: Metabolic alkalosis
  - Water Retention: Heart failure, SIADH
- Symptoms: Muscle weakness, confusion, metabolic alkalosis
Hyperchloremia
- Definition: Serum chloride concentration > 107 mmol/L
- Causes
  - Chloride Excess: Excessive saline infusion
  - Loss of Bicarbonate: Diarrhea, renal tubular acidosis
  - Dehydration: Water deficit
- Symptoms: Lethargy, weakness, metabolic acidosis

Calcium Imbalances

Hypocalcemia
- Definition: Serum calcium concentration < 8.6 mg/dL or ionized calcium < 4.6 mg/dL
- Causes
  - Hypoparathyroidism: Decreased PTH production
  - Vitamin D Deficiency: Impaired calcium absorption
  - Kidney Disease: Decreased calcium reabsorption, increased phosphate
  - Hypomagnesemia: Impairs PTH secretion
- Symptoms: Muscle cramps, tetany, paresthesias, seizures, cardiac arrhythmias
Hypercalcemia
- Definition: Serum calcium concentration > 10.2 mg/dL or ionized calcium > 5.6 mg/dL
- Causes
  - Hyperparathyroidism: Increased PTH production
  - Malignancy: Bone metastasis, ectopic PTH production
  - Vitamin D Excess: Increased calcium absorption
  - Thiazide Diuretics: Increase calcium reabsorption
- Symptoms: Fatigue, weakness, constipation, kidney stones, bone pain, altered mental status

Magnesium Imbalances

Hypomagnesemia
- Definition: Serum magnesium concentration < 1.7 mg/dL
- Causes
  - Poor Dietary Intake: Malnutrition, alcoholism
  - Impaired Absorption: Malabsorption syndromes
  - Increased Excretion: Diuretics, hyperaldosteronism
- Symptoms: Muscle weakness, tremors, seizures, cardiac arrhythmias
Hypermagnesemia
- Definition: Serum magnesium concentration > 2.2 mg/dL
- Causes
  - Kidney Failure: Decreased magnesium excretion
  - Excessive Magnesium Intake: Antacids, laxatives
- Symptoms: Muscle weakness, lethargy, respiratory depression, cardiac arrest

Phosphate Imbalances

Hypophosphatemia
- Definition: Serum phosphate concentration < 2.5 mg/dL
- Causes
  - Decreased Intake: Malnutrition, alcoholism
  - Cellular Shift: Insulin, alkalosis
  - Increased Excretion: Hyperparathyroidism, diuretics
- Symptoms: Muscle weakness, bone pain, seizures, respiratory failure
Hyperphosphatemia
- Definition: Serum phosphate concentration > 4.5 mg/dL
- Causes
  - Kidney Failure: Decreased phosphate excretion
  - Hypoparathyroidism: Decreased PTH production
  - Cellular Release: Tissue damage, hemolysis
- Symptoms: Muscle cramps, tetany, cardiac arrhythmias

Trace Elements

Iron (Fe)
- Iron Deficiency Anemia: Fatigue, weakness, pallor, low hemoglobin, low serum iron, low ferritin, high TIBC
- Hemochromatosis: Fatigue, joint pain, abdominal pain, elevated serum iron, elevated ferritin, elevated transferrin saturation
Zinc (Zn)
- Acrodermatitis Enteropathica: A genetic disorder that affects zinc absorption, leading to skin lesions, diarrhea, and growth retardation
Copper (Cu)
- Wilson’s Disease: A genetic disorder that causes copper to accumulate in the liver, brain, and other organs, leading to liver disease and neurological symptoms
Selenium (Se)
- Keshan Disease: A congestive cardiomyopathy caused by a deficiency of selenium
Iodine (I)
- Iodine Deficiency: Can result in goiter, hypothyroidism, and cretinism (in children)

Key Terms

Electrolyte: An ion that conducts electrical impulses in solution
Cation: A positively charged ion
Anion: A negatively charged ion
Intracellular Fluid (ICF): Fluid within cells
Extracellular Fluid (ECF): Fluid outside cells
Aldosterone: A hormone that increases sodium reabsorption and potassium excretion in the kidneys
Antidiuretic Hormone (ADH): A hormone that regulates water reabsorption in the kidneys
Parathyroid Hormone (PTH): A hormone that increases blood calcium levels
Vitamin D: A hormone that increases blood calcium and phosphate levels
Hemochromatosis: A genetic disorder of iron overload
Hemolysis: The breakdown of red blood cells
Dehydration: A condition caused by the excessive loss of water from the body
Ascites: The accumulation of fluid in the peritoneal cavity, causing abdominal swelling
Edema: Swelling caused by excess fluid trapped in your body’s tissues
Hypovolemia: The medical term for a decrease in blood volume which results in decreased oxygen delivery to the body
Hypoxia: The deficiency in the amount of oxygen reaching tissues
Hypercapnia: The presence of abnormally high levels of carbon dioxide in the blood
Hypoventilation: The state in which a reduced amount of air enters the lungs
Hyperventilation: The state of breathing too fast or too deeply
Paresthesias: An abnormal sensation, typically tingling or pricking (“pins and needles”), caused chiefly by pressure on or damage to peripheral nerves
Carpopedal Spasm: Cramps in the hands and feet
Acromegaly: A disorder that results from excess growth hormone (GH) after the growth plates have closed
Acrodermatitis Enteropathica: A genetic disorder that affects zinc absorption, leading to skin lesions, diarrhea, and growth retardation
Wilson’s Disease: A genetic disorder that causes copper to accumulate in the liver, brain, and other organs, leading to liver disease and neurological symptoms
Keshan Disease: A congestive cardiomyopathy caused by a deficiency of selenium
Cretinism: Hypothyroidism in infants and children is called cretinism
Goiter: An abnormal enlargement of the thyroid gland
Hormone: A regulatory substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action
Atherosclerosis: A disease of the arteries characterized by the deposition of plaques of fatty material on their inner walls
In Vitro: Taking place in a test tube, culture dish, or elsewhere outside a living organism
In Vivo: Occurring within a living organism
Homeostasis: The process by which organisms maintain a relatively stable internal environment
Neuropathy: Weakness, numbness, and pain from nerve damage, usually in the hands and feet

Trace Elements

Procedures