The process by which bone is formed, renewed, and repaired, starting in the embryo and continuing throughout life. There are 3 main situations in which ossification occurs: bone growth, during which new bone forms at the epiphyses (ends) of bones; bone renewal as part of normal regeneration; and bone repair following a fracture.
In newborn babies, the diaphysis (shaft) has begun to ossify and is composed mainly of bone, while the epiphyses are made of cartilage that gradually hardens. In children, growth plates produce new cartilage to lengthen the bones, and further bone forms at secondary ossification centres in the epiphyses. By the age of 18, the shafts, growth plates, and epiphyses have all ossified and fused into continuous bone.
(osteogenesis) n. the formation of *bone, which takes place in three stages by the action of special cells (osteoblasts). A meshwork of collagen fibres is deposited in connective tissue, followed by the production of a cementing polysaccharide. Finally the cement is impregnated with minute crystals of calcium salts. The osteoblasts become enclosed within the matrix as osteocytes (bone cells). In intracartilaginous (or endochondral) ossification the bone replaces cartilage. This process starts to occur soon after the end of the second month of embryonic life. Intramembranous ossification is the formation of a *membrane bone (e.g. a bone of the skull). This starts in the early embryo and is not complete at birth (see fontanelle).
The formation of BONE. In early life, centres appear in the bones previously represented by cartilage or ?brous tissue; and these cells, called osteoblasts, initiate the formation of true bone, which includes the deposition of calcium salts. When a fracture occurs, the bone mends by ossi?cation of the clot which forms between the fragments (see under BONE, DISORDERS OF). In old age, an unnatural process of ossi?cation often takes place in parts which should remain cartilaginous – for example, in the cartilages of the larynx and of the ribs, making these parts unusually brittle.... ossification
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