Calcium-Phosphates
Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. Derangements of this mechanism lead to hypercalcemia or hypocalcemia, both of which can have important consequences for health.
Calcium location and quantity
Calcium is the most abundant mineral in the human body. The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. The extracellular fluid (ECF) contains approximately 22.5 mmol, of which about 9 mmol is in the serum. Approximately 500 mmol of calcium is exchanged between bone and the ECF over a period of twenty-four hours.
Biological functions
1. Structural function: Supporting material in bones. Present as calcium phosphate.
2. Signalling function: Intracellular calcium functions as a second messenger for some hormones.
3. Enzymatic function: Calcium acts as a coenzyme for clotting factors. Calcium also causes the release of Acetylcholine from Pre-synaptic terminal in the transmission of nerve impulse. Calcium causes the contraction of muscles.
Normal ranges
The serum level of calcium is closely regulated with normal total calcium of 2.2- 2.6 mmol/L (9-10.5 mg/dL) and normal ionized calcium of 1.1-1.4 mmol/L (4.5- 5.6 mg/dL). The amount of total calcium varies with the level of serum albumin, a protein to which calcium is bound. The biologic effect of calcium is determined by the amount of ionized calcium, rather than the total calcium. Ionized calcium does not vary with the albumin level, and therefore it is useful to measure the mionized calcium level when the serum albumin is not within normal ranges, or when a calcium disorder is suspected despite a normal total calcium level.
