Mature Bone

concentric lamella osteon

• The matrix of immature bone has more ground substance than does the matrix of mature bone. The matrix in immature bone stains more intensely with hematoxylin, whereas the matrix of mature bone stains more intensely with eosin.

Although not evident in typical histologic sections (Fig. 8.6), immature bone is not heavily mineralized when it is initially formed, whereas mature bone undergoes prolonged secondary mineralization. The secondary mineralization of mature bone is evident in microradiographs of ground sections that show younger Haversian systems to be less mineralized than older Haversian systems (see Fig. 8.19).

Immature bone forms more rapidly than mature bone. Although mature bone is clearly the major bone type in the adult, and immature bone is the major bone type in the developing fetus, areas of immature bone are present in adults, especially where bone is being remodeled. Areas of immature bone are also seen regularly in the alveolar sockets of the adult oral cavity and where tendons insert into bones. It is this immature bone in the alveolar sockets that makes it possible to undertake orthodontic corrections even in adults.

s? cells of bone tissue

As noted above in this chapter, four designated cells are associated with bone tissue: osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts. With the exception of the osteoclast, each of these cells may be regarded as a differentiated form of the same basic cell type. Each undergoes transformation from a less mature form to a more mature form in relation to functional activity (growth of bone). In contrast, the osteoclast originates from a different cell line and is responsible for bone resorption, an activity associated with bone remodeling.

Osteoprogenitor Cells

The osteoprogenitor cell is a resting cell that can transform into an osteoblast and secrete bone matrix

Osteoprogenitor cells are found on the external and internal surfaces of bones. They comprise the periosteal cells that form the innermost layer of the periosteum and the endosteal cells that line the marrow cavities, the osteonal

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