4th most common cation in body. 60% in bone. Required for DNA, protein and parathyroid hormone synthesis.
Plasma concentration is controlled by dietary intake and renal/intestinal conservation
• decrease in plasma concentration – due to GI losses (eg vomiting, diarrhoea), malnutrition/inadequate intake, renal losses (eg ketoacidosis), renal disorders
• neuromuscular irritability – hyperactive deep tendon reflexes, muscle cramps, muscle fibrillation
• CNS hyperexcitability, cardiac arrhythmia’s
• increase in plasma concentration. Rare – kidney is effective as excretion of excess unless have renal disease