Osteoblasts bone remodeling

Pyridinium species comprise collagen cross-links that are formed during bone remodeling by osteoblasts. These cross-links are released into the serum and excreted in... 

Bone remodelling, which continues throughout adult life, is necessary for the maintenance of normal bone structure and requires that bone formation and resorption should be balanced. Bone remodelling occurs in focal or discrete packets know as bone multicellular unit (BMU). In this process, both bone formation and resorption occur at the same place so that there is no change in the shape of the bone. After a certain amount of bone is removed as a result of osteoclastic resorption and the osteoclasts have moved away from the site, a reversal phase takes place in which a cement line is laid down. Osteoblasts then synthesize matrix, which becomes mineralised. The BMU remodeling sequence normally takes about 3 months to produce a bone structure unit (Fig. 2). 

Bone Formation The building of new bone through osteoblasts. Bone formation, which is part of the bone remodelling process, includes the synthesis of organic matter (mostly collagen type 1) and subsequent mineralisation. 

Under normal circumstances, the skeleton undergoes a dynamic process of bone remodeling. Bone tissue responds to stress and injury through continuous replacement and repair. This process is completed by the basic multicellular unit, which includes both osteoblasts and osteoclasts. Osteoclasts are involved with resorption or breakdown of bone and continuously create microscopic cavities in bone tissue. Osteoblasts are involved in bone formation and continuously mineralize new bone in the cavities created by osteoclasts. Until peak bone mass is achieved between the ages of 25 and 35, bone formation exceeds bone resorption for an overall increase in bone mass. Trabecular bone is more susceptible to bone remodeling in part owing to its larger surface area. 

An in vitro cell model resembles the remodeling process of osteoclastic bone resorption followed by osteoblastic bone formation investigate the influence of lead on the communication between these cells determine if lead in the medium (i.e. extracellular fluid) or in the matrix (i.e. in the bone) has different effects on osteoclasts and osteoblasts... 

Teriparatide is a recombinant product representing the first 34 amino acids in human parathyroid hormone. Teriparatide increases bone formation, the bone remodeling rate, and osteoblast number and activity. Both bone mass and architecture are improved. 

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. 

The most important cells implied in bone remodeling are the osteoclasts and osteoblast, although in this process different cellular types such as endothelial... 

For bone substitutes, it is very important that bioceramics have a considerable degree of porosity and particularly interconnected pores so that living bone grows rapidly into the pores. Special bone remodeling cells called osteoclasts and osteoblasts play an extremely important part of the process of rebuilding or repairing the bone. 

Osteoblasts (top) deposit collagen, as well as Ca "" and phosphate, and thereby create new bone matter, while osteoclasts (bottom) secrete H"" ions and collagenases that locally dissolve bone (bone remodeling). Osteoblasts and osteoclasts mutually activate each other by releasing cytokines (see p. 392) and growth factors. This helps keep bone formation and bone breakdown in balance. 

Paget s disease is a syndrome of excessive bone resorption, possibly caused by a virus, in which osteoblastic activity and bone remodelling are abnormal. The bone becomes misshapen as a result, and may be painful. The disease is very common in western countries, and most cases are in fact asymptomatic, but some patients develop bone pain or other complications that require treatment. 

Figure 1. The cellular activity during bone remodelling. At the tip (cutting cone) multi-nucleated osteoclasts (OCLs) excavate the mineralised bone tissue. At some distance, after the resting zone, osteoblasts (OBLs) refill the tunnel with (osteoid) that is subsequently mineralised. Osteocytes (OCYs) are former osteoblasts that were entombed within the bone matrix, but remained connected to the bone surface by numerous long slender protrusions (not visible). Courtesy R. Schenk.

Both cortical and trabecular bone are continuously remodeled through the formation of a bone-modeling unit (BMU), or cutter-cone this process involves activation of osteoclasts, leading to resorption of bone by osteoclasts and formation of new bone by osteoblasts on the site of the old, resorbed bone (Fig. 7) (Martin and Burr, 1989). Under normal physiological conditions (i.e., in the absence of either growth or disease) the dynamics of bone remodeling maintain bone homeostasis throughout a person s lifetime. 

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... 

Parathyroid hormone (PTH) is an 84-amino acid polypeptide hormone that mediates bone remodeling and is an essential regulator of calcium homeostasis. Prolonged exposure to PTH changes the phenotype of the osteoblast from a cell involved in bone formation to one directing bone... 

Nitric oxide (NO) is considered to be a factor that participates significantly in bone remodeling, especially as a mediator of cytokines, and their activities in bone tissue. In cell cultures, the presence of NO leads to an increase of activity of alkaline phosphatase, and to an increase of the number of calcified nodules in the primary line of bone osteoblasts (C3). Low NO concentration, on the other hand, led to increased osteoclast formation. Damoulis and Hauschka (Dl) arrived at a similar conclusion the proinflammatory cytokines induce production of NO in various types of cells, including osteoblasts and osteoclasts. It is obvious that each of these cytokines can interfere in the process of bone remodeling independently of the permissive effect of NO. 

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