The skeletal system, a remarkably diverse arrangement of bones and joints, combines strength with mobility, providing structural support for the body and, in conjunction with the nervous system and muscle, movement and locomotion.

Thick, encasing, and virtually indestructible, bones are fitted to protect vital organs, but appearances can be deceptive. Although the bone's shape and form remain after death, the features necessary for life are lost. It is the cells of bone that are required for its continued existence and its mutability during life.

The cells of bone also provide the mechanism for the other major function of bone, that of a mineral reservoir. The body's requirement for mineral is constant, but the dietary availability is not. During periods of deprivation, mineral can be extracted from bone. Because of the absolute requirement of the rest of the body for minerals, particularly calcium, bone is subservient to these needs. Bone therefore is structurally strong, but also dynamic. In normal adult bone these two needs are balanced by continual remodeling. There is, in the adult animal, little net loss or gain, but a continual turnover of the components of bone.

In growing animals there is an additional need for the net accumulation of bone. In this regard, any dietary deficiency of minerals or vitamins necessary for adequate bone growth will lead to a more rapid development of structural deformity. This chapter discusses the diseases that interfere with the strength and mobility of the skeletal system, and bone as a protector and mineral reservoir.