Chemical Composition of Bone

Chemical Composition of Bone

Bone is made up of both organic and inorganic components. The organic components include osteoid and bone cells. The inorganic components are mineral salts. When both types of components exist in proper amounts, bones are very strong and durable, but are not brittle.

Organic Components

Organic components of bones include osteogenic cells, osteoblasts, bone lining cells, osteocytes, osteo-clasts, and osteoid. Nearly one-third of the matrix is made up of the osteoid. The osteoid includes proteo-glycans and glycoproteins (making up its ground sub-stance) and collagen fibers; both the ground substance and the collagen fibers are made and secreted by osteoblasts. Collagen is the greater contributor to the structure of bones and to their flexibility and tensile strength. Sacrificial bonds inside or between collagen molecules appear to aid in bone resilience. Because they can stretch and break easily when impacted, energy is exhausted. This helps to avoid an actual bone fracture. Most sacrificial bonds reform when trauma is discontinued, over time.

Inorganic Components

The inorganic components of bone are made up of hydroxyapatites or mineral salts, which make up 65% of the bone mass. Mostly made of calcium phosphates, these components are needle-shaped crystals packed tightly in and around the collagen fibers of the extracellular matrix. They are responsi-ble for bone hardness and the ability of bone to resist compression. Combined with organic components of bone, inorganic components provide strength while keeping bones from becoming brittle. Healthy bones may be more easily compressed when they are able to resist tension. They are as strong as steel in resisting tension. Mineral salts in bones enable them to retain their mass even after death, for many years. The long bones of a cadaver still display horizontal growth arrest lines, giving a visible proof of certain illnesses.