Chapter 23 – Bone and Joints

The skeletal system (bones and joints) fulfills several needs in an animal. The skeleton serves as a scaffold on which muscles can act to produce locomotion, provides protection for vital structures, supplies an internal source for minerals, and harbors an environment that supports hematopoiesis. Due to slow and regimented turnover, the current state and the history of a bone coexist. The gross and microscopic structure of each bone depends on its location in the skeleton and the resulting profile of biomechanical forces, as well as on the species, sex, and age. Knowledge of how bone physiology varies due to each of these factors is key in recognizing and understanding bone pathology. In this chapter, basic bone and joint biology, including anatomy, physiology, recent advances in our knowledge of cell–cell signaling, and bone biomarkers are covered in the earlier sections. Animal models, both those found naturally and those generated by genetic or surgical manipulation, can offer great insight into a pathologic process as long as the strengths and limitations of the model are fully appreciated. A review of how bones and joints respond to injury is used to demonstrate the potential range of responses to injurious and restorative events, and the interrelationships between bone cells, is followed by a summary of mechanisms of bone toxicity by various prototypical substances. Many effects on bone in toxicity studies reflect the desired pharmacology of a therapeutic agent, even if the skeleton is not the intended site of action.