Bone Physiology: Bone Cells, Modeling, and Remodeling

Abstract

Key Points• The skeleton undergoes constant change through the processes of modeling and remodeling.• Modeling is defi ned as change in the size or shape of skeletal elements that occurs when formation and resorption are independent e.g., during growth or in an adaptive response to a change in mechanical loading.• Remodeling is defi ned as resorption and formation that occur essentially at the same site and in a programmed manner in which formation is temporally and spatially coupled to resorption. • Modeling and remodeling are achieved by the concerted action of osteoclasts and osteoblasts, either working independently (modeling) or in sequence (remodeling). Both processes are regulated by osteocytes.• Osteocytes also act as mechanosensors, contribute to calcium homeostasis and regulate serum phosphate by secretion of fi broblast growth factor 23.• Bone resorption and formation are regulated a host of endocrine and paracrine factors, including, but not limited to, parathyroid hormone, vitamin D, insulin-like growth factor, receptor activator of nuclear factor kappa B, and sclerostin. • Good nutrition (calcium, magnesium, vitamin D, protein, etc.) is essential for skeletal well-being during growth, adulthood and, particularly, in older age.

Potential Role of Lycopene in the Prevention of Postmenopausal Bone Loss: Evidence from Molecular to Clinical Studies

“…In contrast, bone remodeling occurs throughout life and is responsible for the removal of older bone and its replacement with new bone structure [ 8 , 33 , 34 ]. Bone remodeling involves a sequence of cellular activities that occur within a specialized multicellular unit [ 35 ]. The bone multicellular unit is predominantly comprised of osteoclasts, osteoblasts, and osteocytes [ 24 ].…”

“…There are 3–4 million basic multicellular units (BMU) produced each year, and approximately one million among them actively participate in the bone remodeling process [ 36 ]. Bone remodeling has four major stages: activation, resorption, reversal, and formation [ 35 ]. In the first step, osteoblastic stromal cells or lining cells are activated via lining cell retraction and endosteal membrane digestion by collagenase.…”

Trabecular architecture in the thumb of Pan and Homo: implications for investigating hand use, loading, and hand preference in the fossil record

“…Indeed, debate exists about the potential systemic impact on other areas of the skeleton when one bone/region is loaded (Cresswell, Goff, Nguyen, Lee, & Hernandez, ; Lieberman, ; Sample et al, ; Sugiyama, Price, & Lanyon, ; Wallace et al, ), and how bone remodeling changes in response to differences in age (Nikander et al, ; Pearson & Lieberman, ; Ruff et al, ), muscle (Robling, ) versus joint reaction loading (Judex & Carlson, ; Schipilow, Macdonald, Liphardt, Kan, & Boyd, ), force (Christen et al, ; Schulte et al, ), and even how these factors are balanced against the role of the bone in maintaining homeostasis (Currey, ; Dempster & Raisz, ). Beyond this, large scale genetic studies have identified independent loci for cortical and trabecular bone that are associated with higher risk of fracture (Paternoster et al, ; Yerges et al, ), which suggests certain fixed aspects to bone morphology that may be insensitive to loading.…”

A Comparative Study of the Impact of Dietary Calcium Sources on Serum Calcium and Bone Reformation Using an Ovariectomized Sprague-Dawley Rat Model

“…Another aspect of our results shows the presence of natural protein growth factors [22] and prebiotic non-digestible oligosaccharide fibers [23] in the salmon bone calcium which could be responsible for increased absorption of calcium, in spite of lower levels of elemental calcium intake, as compared to calcium carbonate. In particular, other researchers [24] have shown that the presence of oligosaccharides in the diet can lead to enhanced calcium absorption, particularly when present as part of a functional food.…”