Bone Remodeling is a complex process that requires a well-coordinated activity of osteoblasts and osteoclasts. Osteoclasts are cells that are involved with bone resportion while osteoblasts are involved with bone deposition. The balance between the activities of the two cells ensure that the bones integrity is not compromised at any given time and that calcium levels are maintained at a homeostatic value within the blood (Bartl & Bartl, 2016). Bone remodeling is necessary for the development of secondary bone which is stronger to replace the primary bone in infants. It is also necessary in repair of micro fractures of the bone.
Bone remodeling occurs through 4 stages. The first stage is called activation stage. In this stage, an abnormality of the bone for example a micro fracture is detected by osteocytes which stimulate the release of several factors such as insulin growth factor 1, tumor necrosis factors among others. These factors increase the expression of specific receptors on the surface of the bone which then bind osteoclasts (Bartl & Bartl, 2016) . This leads to the second stage which is known as the resportion stage whereby the osteoclasts start to dissolve bone through either acidification or release of lysozymes that help to breakdown bone. The third stage that follows is called the reverse stage which is carried out by reverse cells. It involves removal of debris after osteoclasts have completed their work of bone resportion. After this is done, the fourth and last stage of bone remodeling called the formation phase starts. During this stage, osteoblasts take charge and start depositing matrix on the areas where osteoclasts have resorbed the bone and once the deposition of matrix is complete, the osteoblasts promote mineralization (Bartl & Bartl, 2016). Thus forming a compact bone.
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Disorders of the osteoclasts or osteoblasts is what causes bone diseases. For example, if the osteoclasts are overworking, they lead to conditions such as osteoporosis is associated with excessive activity of the osteoclasts. Osteopetrosis is as a result of inactivity of the osteoclasts failing to absorb bone.
References
Bartl, R., & Bartl, C. (2016). Modelling and Remodelling of Bone. Bone Disorders , 21–30. doi: 10.1007/978-3-319-29182-6_3
