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Application of chitosan in dentistry—a review
Published in J. Belinha, R.M. Natal Jorge, J.C. Reis Campos, Mário A.P. Vaz, João Manuel, R.S. Tavares, Biodental Engineering V, 2019
J.M.S. Gomes, J. Belinha, R.M. Natal Jorge
The structural scaffold of our body is the skeleton, and the bones that constitute it are key elements for locomotion, antigravity support, life-sustaining functions, and protection of viscera (Graber, Vanarsdall, Vig, & Huang, 2017; Walsh, 2018). Bone tissue is a specialized form of highly vascularized connective tissue which main components are collagen and calcium phosphate (Q. Li, Ma, & Gao, 2015). Bone is divided in cortical and trabecular tissues. The first is a hard and outer layer that surrounds the marrow space, while the latter resembles a honeycomb-like network of interspersed plates and rods, occupying a larger surface area (Clarke, 2008; Walsh, 2018). The cellular component of the bone includes osteoblasts, osteoclasts and osteocytes, each one of them with specific functions. Osteoblasts are responsible for forming bone by synthesizing the organic matrix, which is mainly type I collagen, and for giving bone resistance and tensile forces. On the other hand, osteoclasts, that derive from the monocyte/macrophage cell line, locally degrade the bone matrix during the resorption process. Osteocytes are localized between the bone matrix and are terminally differentiated osteoblasts that convert mechanical loading into biomechanical stimulus (Feng & McDonald, 2011).
Tissue Structure and Function
Published in Joseph W. Freeman, Debabrata Banerjee, Building Tissues, 2018
Joseph W. Freeman, Debabrata Banerjee
Bone also contains several types of cells, and it houses other tissue types. Bones house blood vessels and nerve cells, primarily in the cortical bone. Bones also house osteocytes, which can differentiate into the two cell types responsible for bone remodeling, osteoclasts and osteoblasts. Osteoclasts break down old bone and osteoblasts build new bone. The inner bone cavities contain bone marrow, where red blood cells are produced. Red bone marrow is a soft tissue that produces blood cells, and yellow bone marrow is a store for fat. Bone consists of a mineral phase and a fibrous protein phase. The mineral phase is calcium phosphate, mainly in the form of hydroxyapatite. The mineral is rigid and gives the bone its compressive strength. The main type of protein in bone is type I collagen, which is flexible and gives bone toughness and some elasticity (a small amount).
Introduction to Noninvasive Therapies
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
Bone has a complex physiology and anatomy; on a weight basis, bone is stronger than aluminum, it is a composite material of approximately equal amounts of hydrated proteins and minerals. Three major bone cell classes are osteoblasts, osteocytes, and osteoclasts. Osteoblasts are single-nucleus cells that synthesize bone, functioning in groups of connected cells called an osteon. Osteoblasts synthesize a very dense, cross-linked, Type I collagen, plus several other specialized proteins in smaller quantities (e.g., osteocalcin and osteopontin) which form the organic matrix of bone. Parathyroid hormone (PTH) from the parathyroid gland is an important regulator of blood calcium ion concentration [Ca++], and also the activity of osteoblasts. Osteocytes are star-shaped cells found in all mature bone; they are not capable of mitosis. Osteocytes are long-lived; they do not divide, and have a half-life of ∼25 years. They are derived from osteoprogenitor stem cells, some of which also differentiate into osteoblasts. When osteoblasts become trapped in the matrix they secrete, they become osteocytes. Osteocytes are networked to each other by long cytoplasmic extensions that occupy tiny canals (canaliculi), which are used to exchange nutrients and waste through cellular gap junctions. Osteocytes are actively involved in the routine turnover of bony matrix, through various mechanosensory mechanism. They destroy bone through a rapid, transient mechanism (relative to osteoclasts) called ostocytic osteolysis. Hydroxyapatite [Ca10(PO4)6(OH)2], calcium carbonate, and calcium phosphate are deposited around the cell.
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).
Simulation of the mechanical behavior of osteons using artificial gravity devices in microgravity
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Hao Zhang, Hai-Ying Liu, Chun-Qiu Zhang, Zhen-Zhong Liu, Wei Wang
There is a three-dimensional network throughout osteons that is called the lacunar-canalicular system (LCS). Osteocytes are deeply embedded in the lacunae, on which many synapses pass through the canaliculi to connect with adjacent osteocytes, forming a complex network of osteocytes. Osteocytes regulate bone remodeling by sensing the fluid shear stress (FSS) and other physical information in the LCS caused by external loads, which promotes dynamic regulation of bone mass (Chen and Huo 2017). Although the LCS, the structure of osteocytes and the negative feedback process can prevent unnecessary energy consumption under the reduced load conditions experienced in microgravity, it leads to a large amount of bone loss. During space flight, physical exercise and nutritional supplementation are often used with the aim of reducing bone loss; however, research has found the effect was not significant (Miao et al. 2017). With the increasing distance of human exploration in space, long-term space flight is inevitable. Osteoporosis has become one of the urgent problems in aviation medicine. Artificial gravity (AG) devices aim to simulate Earth-like gravitational acceleration during space flight. As a result, the flow and mechanical properties of the fluid in LCS will return to levels common on the Earth’s surface, thus effectively preventing the loss of bone mass.
Serum sclerostin and cytokine responses to prolonged sculling exercise in highly-trained male rowers
Published in Journal of Sports Sciences, 2021
Jaak Jürimäe, Priit Purge, Vallo Tillmann
Osteocytes, with their mechanoreceptors able to sense mechanical strain, may be involved in bone responses to acute exercise (Pickering et al., 2017). Osteocytes have emerged as a regulator of bone mass through their ability to influence bone remodelling (Pickering et al., 2017). Osteocytes secrete sclerostin, which is an inhibitor of bone formation in osteoblasts by blocking the osteogenic Wnt signalling pathway (Redlich & Smolen, 2012). Typically, athletes have higher circulating sclerostin levels compared to non-athletes (Jürimäe et al., 2016a; Lombardi et al., 2012), while acute increases in sclerostin levels after different modes of high-impact exercises have been reported in untrained participants with different age and sex (Falk et al., 2016; Gombos et al., 2016; Pickering et al., 2017). Recently, similar increases in sclerostin concentrations were observed following short-term high-intensity interval running and cycling exercises in non-athletic participants (Kouvelioti et al., 2018, 2019a). The response of sclerostin to high-intensity interval exercise was independent of exercise impact and was not related to changes in bone turnover markers (Kouvelioti et al., 2018, 2019a). In contrast, sclerostin concentration was not increased after acute resistance exercise in young females (Sharma-Ghimire et al., 2019). Accordingly, the response of sclerostin to acute exercise may depend on the possible interaction of mode, intensity and duration of the exercise and also on the sex, age and physical fitness of the participants.