Composition of Bones
Bone consists of organic and inorganic components . The organic matrix is composed primarily of the protein collagen which provides flexibility and accounts for about 10% of adult bone mass. The main inorganic component is composed of hydroxyapatite, which is an insoluble salt of calcium and phosphorus and accounts for about 65% of adult bone mass. Moreover, bone also contains small amounts of magnesium, sodium, and bicarbonate. In addition, in living adult bone in the body contains between 10 and 20% water.
There are three types of cell present in bone: osteoblasts, osteocytes, and osteoclasts, which are respectively responsible for the production, maintenance, and resorption of bone. The osteoblasts are cuboidal and columnar in shape with a central nucleus found near the surface of bones. They make the proteins that will form the organic matrix of bone and secrete alkaline phosphatase to create sites for calcium and phosphate deposition. The osteoblasts come from bone marrow precursor cells. These precursors are capable of turning into either osteoblasts or fat cells, and various factors determine which kind of cells will be made. One of the factors is called core binding factor alpha l (cbfa1), which will cause the cell to differentiate into an osteoblast . Osteocytes live inside the bone. They can secrete growth factors to stimulate the osteoblasts and sense any mechanical strain on the bone. Osteoclasts are large cells with many nuclei, which resorb the bone. They travel to specific sites on the surface of bone and secrete acids and enzymes which degrade the bone. After they finish resorbing bone, they undergo apoptosis.