Bone remodeling differentiation

The adult skeleton is periodically remodeled by transitory anatomic structures that contain juxtaposed osteoclast and osteoblast teams and that replace old bone with new bone. The purpose of this remodeling is both to prevent bone aging and repair the damage that occurs as well as to guarantee a contribution of minerals, especially calcium, to body cells for their correct function. In the last few years, due mainly to the research in molecular biology and cellular differentiation and to studies of genetically manipulated mice, it has been possible to discover many aspects both of the cellular and molecular bases of this bone remodeling as well as of the differentiation and function of the two main implied cell types osteoblasts and osteoclasts. 

Nutrients necessary for bone remodeling, mesenchymal stem cells (pluri-potent cells capable of differentiating into various cells such as osteoblasts, endothelial cells, and fibroblasts), and hematopoeitic cells (including cells... 

Vitamin A is an essential fat-soluble compound acquired from the diet. The parent form of vitamin A is all-iram-retinol. Vitamin A is needed to maintain normal vision, normal reproduction (including spermatogenesis, conception, and placenta formation), and normal cell differentiation (including bone remodeling, maintenance of differentiated epithelial linings and skin, em-... 

Intramembranous ossification is responsible for most of the mineralization of the skull, including the maxilla and mandible. It begins with the differentiation and activation of osteoblasts from fibroblast-related precursors within a region of connective tissue that demarcates where the bone will develop. The osteoblasts secrete a nonmineralized protein-rich (osteoid) matrix and, as they move away, the matrix mineralizes (Fig. 9.3a). The periosteum remains uncalcified and contains latent and undifferentiated osteoblasts for bone remodeling. Odontoblasts (Ob) and cementoblasts secrete an osteoid-like matrix similar to that of intramembraneous ossification. 

Injury, infection, stress-induced hormones (glucocorticoids), parathyroid hormone (Sect. 10.3.1), and increased pressure on a bone all decrease osteoprotegerin (OCIF) production by osteoblasts, causing greater differentiation of osteoclasts, more bone remodeling, and more... 

Osteoblasts are the primary cells responsible for bone formation. They are derived from mesenchymal (stromal) cells that first differentiate into pre-osteoblasts and then into mature, bone matrix producing osteoblasts. Inactivated or resting osteoblasts become lining cells and thus a reservoir for bone forming cells to be activated at the next remodelling cycle. Osteoblasts trapped and embedded in the mineralised matrix are called osteocyts, and are important for many properties of living bone. 

We have alluded above to the fact that dietary reconstruction from bone can be no more than a relatively long-term average, since in life bone is constantly remodelled. In general, a dietary reconstruction based on bone collagen is likely to represent the average diet of that individual over the last few years of life -perhaps up to as much as ten years before death, depending on the particular bone used. An extension of the isotopic dietary method is to use the differential information available within a single skeleton to study human lifetime mobility. This technique has been developed and exploited most clearly on historic material from South Africa (Sealy et al., 1995 Sealy, 2001 Cox et al., 2001). 

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