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Biochemistry of Exercise Training: Effects on Bone
Published in Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse, The Routledge Handbook on Biochemistry of Exercise, 2020
Panagiota Klentrou, Rozalia Kouvelioti
Bone modelling occurs constantly, enabling bones to adapt to changes in (external) biomechanical forces by changing their morphology/shapes (21, 69). Bone remodelling is an ongoing process that takes place during the lifespan to replace old bone tissue and micro-damaged bone (due to normal daily activity) with new tissue (100). Bone remodelling involves the osteoclasts, osteoblasts, and osteocytes within the bone remodelling cavity and consists of cycles of bone resorption and bone formation, namely bone turnover (133). Bone resorption is the first phase in the remodelling cycle, with the osteoclasts synthesizing and releasing proteolytic enzymes. This results in the removal of minerals and collagen fibres from bone and the destruction of bone extracellular matrix osteoclasts. This phase lasts between 2 and 4 weeks in each remodelling cycle, and its duration is regulated by the apoptosis of osteoclasts (100, 133). Bone formation lasts 4 to 6 months with the osteoblasts synthesizing new bone extracellular matrix (133). About 5–10% of total body bone mass is going through this process of remodelling every year with each remodelling cycle lasting between 2 to 8 months (69). About 4% of compact bones and 20% of spongy bones are renewed every year, with different rates of remodelling in different regions of the body. New osteons are produced through this process of remodelling, providing storage of minerals required for various metabolic functions (136).
Introduction and Review of Biological Background
Published in Luke R. Bucci, Nutrition Applied to Injury Rehabilitation and Sports Medicine, 2020
Bone itself is subdivided into contiguous units called osteons (Haversian systems) based on concentric lamellar layers of calcified osteoid matrix surrounding a central Haversian canal. Osteocytes (osteoblasts) occupy interconnected lacunae within each osteon. Thus, each osteocyte is able to remain readily accessible to its blood supply, which makes bone an interactive, metabolically active, hormonally responsive tissue. The usual diameter of osteons corresponds to the limit of diffusion from the central canal of nutrients. Bone receives 10% of cardiac output and is richly endowed with blood vessels and nerves. Lymphatics are located in the periosteum. The blood vessels inside of bone are thin and have frequent anastomoses, sinusoids, and plexi. Venous supply has six to eight times greater capacity than arterial supply, in order to accommodate entry of new blood cells from marrow and facilitate metabolism of mineral ions.
Animal Models of Osteopenia or Osteoporosis
Published in Yuehuei H. An, Richard J. Friedman, Animal Models in Orthopaedic Research, 2020
Donald B. Kimmel, Erica L. Moran, Earl R. Bogoch
The adult dog is generally a reliable model of the adult human skeleton. Haversian and cancellous osteons remodel as in humans, though more rapidly.127 Skeletal findings in the adult dog parallel the adult human for corticosteroids,128,129 uremia,130 bisphosphonates,131 and PTH excess.132 In contrast to all other uses for the adult dog as a model of the adult human skeleton, the OVX dog is problematic. Many individual studies lack significance, but the data in bulk133 suggest that 8-10% annual bone loss occurs in newly-OVX dogs. Most studies indicate a minor transient post-OVX rise in bone formation, but some134 suggest that formation falls rapidly by 50%, without a transient increase. The latter suggests a dissimilarity to findings in transmenopausal humans and other animals, where the transient turnover rise34 is well known.31 ERT tends to suppress turnover, but with uncertain effects on bone mass.135 E2 levels in the dog are usually very low, rising twice yearly.136 E2 spikes in rats for 18 hours every four d82 and monthly in women.137 The estrus cycle in monkeys is similar to humans, but E2 peaks only about half as high.138 Dogs’ integrated E2 exposure, only marginally less than in rats, is only one-fourth that in humans and similar to primates, except for the peaks. These differences could cause the dog to develop only a small estrogen-dependent cancellous bone compartment.
Simulation study on the effect of resistance exercise on the hydrodynamic microenvironment of osteocytes in microgravity
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Hai-Ying Liu, Chao-Hui Zhao, Hao Zhang, Wei Wang, Qing-Jian Liu
Bone is typically comprised of dense bone, cancellous bone, and tissue fluid. The osteon is the basic structural and physiological unit of dense bone, and it also has the highest bone density in the human skeletal system (Liu et al. 2020; Larcher and Scheiner 2021). The central tubular area of the osteon is called the Haversian canal, which contains arterial and venous capillaries that permit the transport of nutrients and metabolic waste needed for cell metabolism. The multi-layer circumferential lamellae around the Haversian canal consist of a complicated lacunar-canalicular system (LCS). The osteocytes are located in bone lacunae, and the adjacent osteocytes form a complex spatial mechanical signal transduction network through synaptic connections in the canaliculi. The LCS is an important channel for material exchange between osteocytes and capillaries in the Haversian canal (Kwon et al. 2010). The deformation of the bone matrix under loading can induce liquid flow in the LCS, and the mechanical signals produced by the liquid flow are perceived and responded to by osteocytes, thus regulating the activity of osteoblasts and osteoclasts to adjust bone mineral density to adapt to the current mechanical environment (Tovar et al. 2004).
Effects of irradiation in the mandibular bone loaded with dental implants. An experimental study with a canine model
Published in Ultrastructural Pathology, 2021
Sridhar Reddy Padala, Pekka Asikainen, Timo Ruotsalainen, Jopi JW Mikkonen, Tuomo S Silvast, Arto P. Koistinen, Engelbert A.J.M. Schulten, Chris M. Ten Bruggenkate, Arja M. Kullaa
Osteocytes are considered the major mechanosensory cells of the bone remodeling process.24 The maintenance of bone around the implant is directly dependent on the osteocytic lacunar canalicular system (OLCS) constitution.33 In a recent study by Mendes et al.13 showed a decrease in the number of osteocytes and increased empty lacunae after irradiation, which might negatively affect the mechanosensation system resulting in impaired bone repair. We demonstrated histological alterations in the bone around the implants through LM, BFM, and SEM. Osteocytes located parallel to the new bone layer attached to the implant with few canalicular processes are observed in irradiated than in the control bone. We did not find empty cellular lacunae, but osteocytes were observed under SEM. This study demonstrated the osteocytes without osteons in the bone adjacent to implants and confirmed the finding that the newly formed bone changed to the compact bone by continuous bone remodeling as suggested by Haga et al.33
Drug-eluting implants for the suppression of metastatic bone disease: current insights
Published in Expert Review of Medical Devices, 2018
Ippokratis Pountos, Peter V. Giannoudis
Current literature has several limitations. With regards to experimental models, small animal models where cancers cells are implanted can be criticized for the uncomparable bone structure and biology. Bone structure with secondary osteons to reflect human bone is ideal, with rodents to pose plexiform bone or permissive bone healing. On the other hand, large animal models like dogs and pigs have similar bone structure but are expensive and difficult to manage [70–73]. In addition a suitable model should allow sufficient time for the experiments to make the outcomes clinically relevant [70,73]. Another drawback is the inhomogeneity of the studies regarding the used drugs concentrations. At present there is no commercially available cement preparation that elutes chemotherapeutic agents, the preparation is done in the operating room [51]. The future in local drug delivery devices seems to incline toward coupling systems that allow a precise controlled release of the therapeutic agents together with their degradation and replacement by bone. Smart implants aiming to stabilize the bone and suppress tumor progression is also an emerging promising approach.