The human skeleton is a complex organ system comprised of a collection of many individual bones that are brought together by connective tissue to accomplish not only a biomechanical and supportive function, but also a homeostatic role. The skeleton plays a pivotal role in providing a metabolic supply for the body, supplying the body with calcium and phosphorous that is needed for a plethora of cellular processes. To accomplish this dual role, bone cells have the capability to respond to both local cytokines and circulating hormones. Osteocytes, osteoclasts, and osteoblasts form the main cellular component of bone. Osteoclasts are bone resorbing cells while osteoblasts are bone forming cells. The adult skeleton goes through a continuous process of bone renewal called remodeling. Mediated by osteoclasts and osteoblasts, remodeling replaces old bone with new bone. Although it has long been known that these cells both arise from bone marrow progenitors, the extent to which the differentiation pathways interact and depend on one another has been studied only recently. It has been hypothesized that the local actions of cytokines play a crucial role in these intercellular signaling cascades. In addition, exercise (mechanical loading on bone) has been shown to generate an anabolic effect via regulation of cytokine secretion and intracellular signaling pathways, such as Wnt signaling, in bone cells.
Last date updated on July, 2014