Читать книгу Musculoskeletal Disorders - Sean Gallagher - Страница 101

Osteoclasts differentiate after the fusion of bone marrow‐derived mononuclear precursor cells of the monocyte–macrophage lineage in a process termed osteoclastogenesis. Osteoclasts are large multinucleated cells with a ruffled bottom in contact with the bone matrix (Figure 3.17d). They work in concert with osteoblasts in the constant turnover and remodeling of bone. They do this via their ability to secrete hydrochloric acid and other degradative enzymes, which, once activated, dissolve the bone matrix, creating a resorption pit underneath the cell. Osteoclasts are regulated by parathyroid hormone, calcitonin (from the thyroid gland), and pro‐inflammatory cytokines (Boyce & Xing, 2007; Brabnikova Maresova, Pavelka, & Stepan, 2013; Nakashima & Takayanagi, 2011). As mentioned earlier, osteoclast activation is also mediated by the binding of osteoblast or osteocyte produced RANKL (a protein that plays an essential role in the recruitment, differentiation, activation, and survival of osteoclasts) (Burgess et al., 1999). Estrogen has a dual effect: Its presence increases bone formation and reduces bone resorption by enhancing osteoblast proliferation and function (Ernst, Heath, & Rodan, 1989; Majeska, Ryaby, & Einhorn, 1994); it also reduces bone turnover by reducing osteoclast activity (Hofbauer et al., 1999).