Calcium exchange between bone and extracellular fluid

2021-06-07 04:18 PM

A small part of this readily exchangeable form of calcium is also the form of calcium found in all tissue cells, especially in highly permeable cells such as the liver and gastrointestinal tract.

If soluble calcium salts are administered intravenously, calcium ion concentrations may immediately rise to a high threshold. However, within 30 to 60 minutes, calcium ion levels return to normal. Similarly, if large quantities of calcium ions are removed from the circulating mass, calcium ion concentrations return to normal within 30 minutes to 1 hour.

These effects are because bone contains readily exchangeable calcium which is always in equilibrium with calcium ions in the extracellular fluid.

A small part of this readily exchangeable form of calcium is also the form of calcium found in all tissue cells, especially in highly permeable cells such as the liver and gastrointestinal tract. However, most of this calcium is concentrated in the bones. It usually accounts for about 0.4-1 percent of total bone calcium. This calcium is deposited into the bone in the form of readily mobilized salts such as CaHPO4 and amorphous calcium salts.

Easily exchangeable calcium is important because it provides a rapid buffering mechanism to keep the calcium ion concentration in the extracellular fluid from an excess or a deficiency back to normal values.