Metabolism of Calcium:
The concentration of calcium in the plasma is kept in the range of 9-11 mg/dl. About 40% of the calcium is bound to plasma protein and 60% is diffusible. The plasma level is regulated by:
1. The active form of vitamin D
2. Parathyroid hormone
3. Calcitonin is a hormone secreted by the thyroid gland.
When the plasma level of calcium is lowered, parathyroid hormone secretion increases. This hormone activates the conversion of vitamin D to its active form in the kidney. The calcium level in the blood is increased by three actions:
1. Increased absorption from the intestinal tract.
2. Release of calcium from the bones called resorption.
3. Increased re-absorption of calcium by the renal tubules.
Bone:
Bone consists of organic and inorganic substances. The main organic substance is the protein collagen and the ground substance consist of small amounts of mucoproteins and mucopolysaccharides. The formation of bone is initiated early in foetal life with the development of the cartilaginous matrix. During the latter part of pregnancy some mineralization of the foetal skeleton takes place so that the infant at birth has a body calcium content of about 28g.
Teeth:
Like bones, teeth are complex structures consisting of a protein matrix and mineral salts, basically calcium and phosphorus. In the foetus the development of teeth begins by the fourth the development of teeth begins by the fourth month and calcification proceeds during the growing of the foetus. These teeth of the infant are fully mineralized by the end of the end of the first year of life, but calcification of permanent teeth is completed at various times during childhood and adolescence. The turnover of calcium in teeth is very slow, but unlike the bone, once the calcium in teeth is lost, it can’t be replaced.