Electrolytes

Question 1

Importance of electrolytes

Answer 1

Essential for bodily function - heart cannot beat and brain can’t send/ receive nerve impulses

Question 2

What is a cation

Answer 2

Positively charged ion

Question 3

What is an anion?

Answer 3

Negativity charged ion

Question 4

Note on Calcium (Ca2+)

Answer 4

Function: bind to phosphate ions forms calcium phosphate - increases rigidity & hardens bones & enamel of bones - blood clotting, nerve impulses, muscle movement
Reference Range: 2.1 - 2.6 mmol/L
Deficiency: Hypocalcaemia - hypoparathyroidism, nephrotic syndrome, ricketts, renal failure
Excess: Hypercalcemia - primary hyperparathyroidism, multiple myeloma, metastic bone lesions & high vitamin D
Testing: colorimetric assay - spectrophotometer @ 540nm
Ca2+ + ortho-cresolphthalein = (pH 10.6 + 8-hydroxyquinoline) Ca-ortho-cresolphthalein complex(violet)
Notes: most abundant cation - 1.5% body weight - 99% in bones and teeth - release of Ca into blood by parathyroid hormone, uptake of Ca from blood by calcitonin

Question 5

Notes on Sodium (Na+)

Answer 5

Function: nerve & muscle function - regulates fluid level in the body
Reference Range: 120 - 145 mmol/L
Deficiency: hyponatraemia - sodium loss, excess water, Addison’s disease (increased ADH production), nephrotic syndrome (increased water retention)
Excess: Hypernatraemia - dehydration, possibly high salt intake
Testing: Ion selective electrode (ISE) or flame photometry
Notes: present in all body fluids

Question 6

Notes on potassium (K+)

Answer 6

Function: nerve function, muscles contract, heatbeat stay regular, helps move nutrients into cells & waste out of the cell
Reference Range: 3.5-5.0 mmol/L
Deficiency: Hypokalaemia - low dietary intake over long time, increased loss (kidneys, vomiting, diarrhoea), increase secretion of aldosterone, some diuretics
Excess: Hyperkalaemia - metabolic renal tubular acidosis (hypoaldosteronism) & kidney disease
Testing: ISE methodology
Notes: Diet rich in potassium offset harmful effect of sodium
↑K ↓Na

Question 7

Notes on Magnesium (Mg2+)

Answer 7

Function: 300 biochemical reactions - regulate blood pressure & heartbeat - maintain bone strength
Reference Range: 0.7-1 mmol/L
Deficiency: Hypomagnesaemia - inadequate magnesium intake, absorption, increased excretion, & diuretic drugs (furosemide)
Excess: Hypermagnesaemia - kidney failure, magnesium salts & drugs that contain magnesium
Testing: Arezano method - dyes preferentially with magnesium - absorbance measured at 572nm - spectrophotometry

Question 8

Notes on Chloride (Cl-)

Answer 8

Function: Works with electrolytes such as potassium, sodium, bicarbonate - regulate the amount of fluid & pH balance
Reference Range: 98-106mmol/L
Deficiency: Hypochloraemia - hyponatraemia causes
Excess: Hyperchloraemia - dehydration, hypernatraemia due to Cushing’s Syndrome or kidney disease, too much base is lost (bicarbonate ions), & hyperventilation (causes respiratory alkalosis)
Testing: ISE methodology
Notes: usually reflects sodium levels - except acid-base disorders

Question 9

Notes on Phosphate (HPO4-)

Answer 9

Function: Build & repair bones, muscle contractions, nerve function,
Reference Range: 0.8 - 1.4 mmol/L
Excess: kidney damage - control phosphate levels
Testing: Colorimetric method
Phosphate + ammonium molybdate(blue) = (acidic) phosphomolybdate complex
Inorganic phosphorus reacts with ammonium molybdate in acidic conditions to form coloured complex - absorbance at 365nm spectrophotometer
Notes: ↑Ca2+ ↓HPO4- controlled by PTH

Question 10

Notes on Bicarbonate (HCO3-)

Answer 10

Reference Range: 22-29 mmol/L
Testing: Part of an electrolyte panel
Notes: used for pH determination - diagnosis of respiratory & metabolic acid-base disorders