3. Metabolism of Bone and its Remodeling

Moreover, the bone lining cells, together with other bone cells, are an important component of the BMU, an anatomical structure that is present during the bone remodeling cycle [ 9 ]. These findings suggest that besides professional phagocytes, osteoblasts are also able to engulf and degrade apoptotic bodies during alveolar bone formation [ 49 ]. Zhang et al. Recent studies also suggest the existence of other factors involved in the coupling mechanism during the bone remodeling cycle.

Bone remodeling - Wikipedia

Key Terms osteon: These diseases are caused by an inadequate or delayed mineralization of osteoid. Bone growth modeling is the most intensive in the childhood and adolescence, before reaching full maturity. On the contrary, obese people do not suffer a significant loss of bone tissue because their bones are more consistently loaded — a load is one of the main regulating mechanisms. One of the most important extra-skeletal biologically active compounds regulating bone remodeling is serotonin 5-hydroxytryptamine ; serotonin receptors are expressed on the plasma membranes of osteoblasts, osteoclasts, and osteocytes de Vernejoul et al.

In the initiation phase, under the action of osteoclastogenic factors including RANKL and M-CSF, hematopoietic stem cells are recruited to specific bone surface areas and differentiate into mature osteoclasts that initiate bone resorption [ , ].

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Osteoporosis means porous bone, which is caused by an over-reaction to osteoclastic bone resorption, and makes bones quite fragile for the elderly. Uninterrupted osteogenesis in this period is a prerequisite for normal mechanical properties of the bones and their resistance to various pathologies, e.

The number of osteoblasts tends to decrease with age, affecting the balance of the formation and resorption in the bone tissue, and potentially leading to osteoporosis. Tummala, and C.

The systemic factors which are important to the maintenance of bone homeostasis include parathyroid hormone PTH , calcitonin, 1,dihydroxyvitamin D 3 calcitriol , glucocorticoids, androgens, and estrogens [ 16 , — ].

These channels are formed by proteins called annexins [ 40 ].

The number of organelles such as rough endoplasmic reticulum and Golgi apparatus decreases, and the nucleus-to-cytoplasm ratio increases, which correspond to a decrease in the protein synthesis and secretion [ 58 ]. Taniwaki and E.

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The development of the primary and secondary ossification centers. Ye et al. Mesenchymal stem cells initiate the process of intramembranous ossification.

Bone is composed by inorganic salts and organic matrix [ ]. Understanding the molecular background of these two conditions provided novel therapeutic options for patients with excessive bone formation and individuals with osteoporosis McClung et al.

Bone remodeling occurs in response to various factors, e. Andersen, T. Hayashi, T. This phenomenon is observed either under physiological conditions, as an effect of dynamic forces generated during usual everyday activities or during regeneration of the bone after trauma. The mechanisms by which estrogen act on bone tissue are not completely understood. Markers of bone resorption Bone resorption markers include: Nevertheless, several studies have shown that estrogen maintains bone homeostasis by inhibiting osteoblast and osteocyte apoptosis [ — ] and preventing excessive bone resorption.

As polarized cells, the osteoblasts secrete the osteoid toward the bone matrix [ 24 ] Figures 1 a , 1 b , and 2 a.

3. Metabolism of Bone and its Remodeling • Functions of Cells and Human Body

Delorme, F. Bone metabolism is regulated by many systemic hormones and locally acting substances. It has been suggested that estrogen decreases osteoclast formation by inhibiting the synthesis of the osteoclastogenic cytokine RANKL by osteoblasts and osteocytes. S—S, Ito et al.

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Riggs, and T. Barragan-Adjemian, L. This process occurs due to coordinated actions of osteoclasts, osteoblasts, osteocytes, and bone lining cells which together form the temporary anatomical structure called basic multicellular unit BMU [ 12 — 14 ]. Bone remodeling is a complex process modulated by a number of factors taking place simultaneously at many sites.