There are alterations in the rates of bone resorption and bone formation at different stages during life (Fig. 18.6). During adolescence, bone formation is relatively greater than bone resorption so that there is an increase in skeletal mass. In young adult life there is a perfect balance between bone resorption and bone formation, and skeletal mass remains constant. After the middle of the third decade, however, there is usually an increase in bone resorption relative to bone formation and bone is progressively lost.
