Chemical Composition of Bone

most notable characteristic of bone

The crystals account for the most notable characteristic of bone—its exceptional hardness, which allows it to resist compression.

what are the organic components of bone?

one-third of the matrix, includes ground substance which is composed of proteoglycans, glycoproteins and collagen fibers

Chemical Composition of Bone

Bone has both organic and inorganic components. Its organic components include the cells (osteogenic cells, osteoblasts, osteocytes, and osteoclasts) and osteoid (os′te-oid), the organic part of the matrix. Osteoid, which makes up approximately one-third of the matrix, includes ground substance (composed of proteoglycans and glycoproteins) and collagen fibers, both of which are made and secreted by osteoblasts. These organic substances, particularly collagen, contribute not only to a bone's structure but also to the flexibility and great tensile strength that allow the bone to resist stretch and twisting. Bone's exceptional toughness and tensile strength has been the subject of intense research. It now appears that this resilience comes from the presence of sacrificial bonds in or between collagen molecules that break easily on impact, dissipating energy to prevent the force from rising to a fracture value. In the absence of continued or additional trauma, most of the sacrificial bonds re-form. The balance of bone tissue (65% by mass) consists of inorganic hydroxyapatites (hi-drok″se-ap′ah-tītz), or mineral salts, largely calcium phosphates present in the form of tiny, tightly packed crystals in and around the collagen fibers in the extracellular matrix. The crystals account for the most notable characteristic of bone—its exceptional hardness, which allows it to resist compression. The proper combination of organic and inorganic matrix elements allows bones to be exceedingly durable and strong without being brittle. Healthy bone is half as strong as steel in resisting compression and fully as strong as steel in resisting tension. Because of the salts they contain, bones last long after death and provide an enduring "monument." In fact, skeletal remains many centuries old have revealed the shapes and sizes of ancient peoples, the kinds of work they did, and many of the ailments they suffered from (arthritis, for example).

Bone Development

Ossification and osteogenesis (os″te-o-jen′ĕ-sis) are synonyms meaning the process of bone formation (os = bone, genesis = beginning). In embryos this process leads to the formation of the bony skeleton. Later another form of ossification known as bone growth goes on until early adulthood as the body continues to increase in size. Bones are capable of growing in thickness throughout life. However, ossification in adults serves mainly for bone remodeling and repair.