Interaction calcium and phosphate

Calcium and phosphate ion physiology is closely related:

• if the product of the concentration of each ion exceeds a value that is termed their solubility product, they precipitate out of solution. This can result in new mineralization within bone or ectopic calcification. Conversely, the equilibrium results in one ion being reabsorbed from bone if the concentration of the other drops. Therefore, a large drop in plasma phosphate concentration can cause hypercalcaemia.
• parathyroid hormone causes renal reabsorption of calcium but reduces phosphate reabsorption
• 1,25-dihydrocholecalciferol promotes gastrointestinal absorption of both calcium and phosphate

However, unlike the free, ionized plasma concentration of calcium, the concentration of ionized phosphate fluctuates considerably throughout the day.