Attributes of Peripheral Dopamine and Dopamine Receptors
Nira Ben-Jonathan in Dopamine, 2020
Bone is a rigid structure that constitutes part of the vertebrate skeleton. Bones fulfill multiple functions, including support of the body to enable motility, protection for various organs, production of red and white blood cells (in the bone marrow), and storage of minerals. Bone is composed of three primary cell types: osteoblasts, osteocytes, and osteoclasts. Osteoblasts are bone-forming cells that generate a protein mixture known as osteoid, composed of type I collagen, which upon mineralization becomes bone. They also manufacture hormones such as prostaglandins and robustly produce alkaline phosphatase, which is involved in bone mineralization and the formation of matrix proteins. Osteocytes are mature bone cells, which originate from the osteoblasts and migrate into the bone matrix in spaces called lacunae. Osteocytes have many processes that contact osteoblasts and other osteocytes, forming a communication network. Their functions include the formation of bone, the maintenance of matrix, and calcium homeostasis. Osteoclasts are the cells responsible for bone resorption and remodeling. They are large, multinucleated cells located on bone surfaces in resorption pits. Because osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with phagocytic-like mechanisms similar to circulating macrophages.
The skeleton and muscles
Frank J. Dye in Human Life Before Birth, 2019
During the second half of the embryonic period (which, recall, makes up the first 8 weeks of development), bone formation begins. Although the skeleton has a structural role, as well as a role in movement, unlike other structural elements, such as the steel girders that support a building, bones are dynamic entities. The dynamic nature of bone is realized from a consideration of the types of cells in bones and their functions. There are four types of cells associated with bones: osteoblasts, osteoclasts, osteocytes, and osteogenic cells. The osteoblast is the bone cell responsible for forming new bones; they do not divide, but synthesize and secrete the collagen matrix and calcium salts that make up bones. As the osteoblast becomes surrounded by calcified matrix, it becomes trapped within it, changes its shape, and becomes an osteocyte. The osteocytes, the primary cells of mature bone and the most common type of bone cell, maintain the mineral concentration of the matrix. Like osteoblasts, osteocytes also do not divide; both cell types are replenished by osteogenic cells, which are the only bone cells that divide. The dynamic nature of bone depends on the creation of new bone by osteoblasts and osteocytes and by the resorption (breakdown) of bone by the fourth type of bone cell, osteoclasts. Unlike osteoblasts and osteocytes, which arise from osteogenic cells, osteoclasts originate from monocytes and macrophages (two types of white blood cells). The continual balance between osteoblasts and osteoclasts is responsible for the constant, albeit subtle, reshaping of bone.
Introduction and Review of Biological Background
Luke R. Bucci in Nutrition Applied to Injury Rehabilitation and Sports Medicine, 2020
The cells that produce, maintain, and repair bone are known as osteoblasts. Like chondrocytes, osteoblasts have encased themselves in extracellular matrix (bone), but unlike chondrocytes, osteoblasts enjoy a rich blood supply and direct links to adjacent osteocytes in canaliculi. The ability of osteoblasts to respond to trauma enables bone to regenerate and heal completely. Furthermore, bone is constantly being remodeled, which means that osteoblasts are periodically required to produce osseous matrix. Osteoblasts synthesize bone tissue by first depositing osteoid or organic bone matrix. Osteoid is composed of collagen, PGs, and noncollagenous proteins that resemble cartilage. Mineralization of osteoid proceeds with the assistance of specialized proteins and after removal of most PGs. Osteoblasts are hormone-responsive, which greatly affects how these cells convert nutrients into bone. Rapid mobilization of calcium and other minerals (magnesium, phosphate, zinc, copper) from lacunae surfaces is termed osteocytic osteolysis and is vital for maintenance of serum calcium levels.
Alveolar bone remodeling after tooth extraction in irradiated mandible: An experimental study with canine model
Published in Ultrastructural Pathology, 2018
Venni Heinonen, Timo J. Ruotsalainen, Lauri Paavola, Jopi J. Mikkonen, Pekka Asikainen, Arto P. Koistinen, Arja M. Kullaa
Bone remodeling process is performed by osteoclasts (bone resorbing cells) and osteoblasts (bone forming cells) at the bone surface. Osteocytes, most abundant bone cells, are believed to be responsible for the bone remodeling.10 Osteocytes react to dynamic and/or static loading such as gravity or exercise, and they are the most common cell type found in bone matrix, comprising more than 90% of all bone cells in mature bone. Osteocytes are derived from osteoblasts that are trapped under the mineralized bone matrix, and form a cellular network, called as lacunar-canalicular network (LCN), which allows communication between neighboring osteocytes, osteoblasts, and bone lining cells. Long dendritic processes of the osteocytes convey signals to the neighboring osteocytes and the cells of the bone surface.11 With this network, osteocytes control bone metabolism, and bone homeostasis (breakdown and formation of bone) by producing bone formation and/or resorption proteins.11,12
Multi-scale numerical simulation on mechano-transduction of osteocytes in different gravity fields
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Chaohui Zhao, Haiying Liu, Congbiao Tian, Chunqiu Zhang, Wei Wang
Osteocytes ‘communicate’ with cells on the bone surface and other surrounding osteocytes through osteocyte processes. The tethering elements (TES) are arranged in a double helix along the axial direction of the canaliculi; one end of the TES is connected to the cross filament by transmembrane molecules and fixed to the cell membrane, and the other end is anchored to the inner wall of the canaliculus (You et al. 2004). The resistance to the pericellular matrix (PCM) induced by the flow of tissue fluid in the lacuna-canalicular system (LCS) can make TES ‘perceive’ higher mechanical stimulation. As a result, TES can effectively convey mechanical signals to the surface of the osteocyte process, and the surrounding area of physical connection between the osteocyte process and the TES can produce higher strain. TES can increase the initial strain by several orders of magnitude as a force transfer element in the stress and strain amplification mechanism (You et al. 2004). The strain amplification mechanism can compensate for the strain difference between osteocytes and bone tissue (Han et al. 2004; Wang et al. 2007).
The interaction between vitamin C and bone health: a narrative review
Published in Expert Review of Precision Medicine and Drug Development, 2018
Alberto Falchetti, Roberta Cosso
As mentioned earlier, age-related oxidative stress is crucial in massive skeletal decline and bone strength loss. For instance, osteocytes live up to 50 years, while OCLs and OBLs have a shorter lifespan, and their death depends on the skeletal age [33]. Specifically, in in vitro and in vivo models, free radicals induce apoptosis of OBLs and OCLs and, therefore, bone resorption. Mitochondrial ROS form because some electrons do not complete the series of the oxidative phosphorylation chain, and the efficiency depends on cytochrome c oxidase activity [29]. In mice, oxidative stress was shown to antagonize the Wnt pathway, necessary for correct osteoblastogenesis from precursor cells [34]. Moreover, oxidative stress is linked to age-related insulin resistance, as frequently observed in the elderly and obese population, with suppression of OBLs and bone formation. As reported above, vitamin C, as well as vitamin E and other antioxidants, are able to enhance mitochondrial function. For this reason, their use is recommended to treat the consequences of mitochondrial dysfunction, although their efficacy is too limited and not largely supported in clinical studies [35,36].
Related Knowledge Centers
- Dmp1
- Gap Junction
- Hydroxyapatite
- Lacuna
- Mesenchyme
- Osteolysis
- Osteoclast
- Osteoblast
- Cell
- Bone Canaliculus