Mature bone formation

Bone metabolism comprises the processes of bone formation and bone resorption, the key actions by which skeletal mass, structure and quality are accrued and maintained throughout life. In the mature skeleton, anabolic and catabolic actions are mostly balanced due to the tight regulation of the activity of bone forming ( osteoblast) and bone resorbing ( osteoclast) cells through circulating osteotropic hormones and locally active cytokines. 

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. 

Miller, J., Horner, A., Stacy, T., Lowrey, C., Lian, J., Stein, G., Nuckolls, G. and Speck, N. (2002) The core binding factor beta subunit is required for bone formation and hematopoietic maturation. Nat Genet 22, 645-649. 

The spaces between the ends of the tropocollagen molecules in a collagen fiber (see Fig. 4) are the nucleation sites for the deposition of a form of calcium phosphate, hydroxyapatite, in bone formation. Further hydroxyapatite is added until the nucleation sites grow and join with one another to form the mature bone structure. 

Copper The content of Cu in the human body is estimated to range between 50 and 80 pg. The RDA is 1.5-3.0 mg per day for adults. Copper is an essential component of several enzymes and is required in bone formation, cellular respiration, cardiac function, connective tissue development, and myelination of the spinal cord [11-14]. This metal is also necessary for Fe absorption and mobilization. Again, Cu content in milk differs with the biological species, stage of lactation, and diet intake. In all species colostrum is substantially richer in Cu than mature milk is. 

Endochondral ossification is the gradual replacement of cartilage by bone during development. This process is responsible for formation of most of the skeleton of vertebrate animals. In this process, actively dividing bone-forming cells (osteoblasts) arise in regions of cartilage called ossification centers. The osteoblasts then develop into osteocytes, which are mature bone cells embedded in the calcified (hardened) part of the bone known as the matrix. 

Paradoxically, whereas aging is associated with a decrease in bone formation [121], it is also linked to vascular calcification [122]. Vascular calcification can form by intramembranous ossification or by endochondral bone formation, and eventually lead to the appearance of mature bone, with bone marrow, in the vasculature... 

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