Osteoclast: The Leading Actor in Bone Disorders

Abstract

Bones are not inert, amorphous, rocklike substances, but are alive, sensible and dynamic like other tissues of the body. As indicated in the previous chapter, bone is subject to constant stress, maintenance, adaptation and repair. They get atrophic when they are not used, they die if they have no sufficient blood supply, they develop inflammations and tumours, they respond to various systemic and local influences and, especially, they can heal themselves. Considering the dynamic behaviour and pathologic consequences, one cell type of the osseous tissue is almost always involved and plays a major role both in normal and pathologic reactions: the osteoclast, belonging to the monocyte-macrophage-system. Anomalies and alterations in activity of this specific cell result in localised or systemic disorders of the bone and can manifest as: