The skeleton is an important reservoir of calcium, serving both a maintain plasma calcium concentrations and to make optimal use of ingested calcium.
Nearly all (99%) of total body calcium is located in skeleton. It serves both functions mainly by adjusting the balance between bone formation and bone resorption.
Another 1% is equally distributed between the teeth and soft tissue, with only 0.1% in the extracellular fluid.
In the plasma there is also a protein bound calcium fraction, which is present at concentration of 3.2 mg/100 ml (0.8 mmol/l).
About 50% calcium in plasma is ionized and 10% is complexed with citrate phosphate, bicarbonate and lactase.
From birth to approximately 20 years of age, when skeleton reaches its full size and density, calcium content increases by some 40 fold.
Calcium distribution in human body
