Bone remodelling (or resorption) is a life-long process. This is a process where old or mature bone tissue is removed from the skeleton and new bone tissue is formed (called ossification). In fact, in the first year of life almost 100% of the skeleton is replaced!!
How does this happen?
The cells responsible for bone metabolism are called osteoblasts (which secrete new bone), and osteoclasts (which break bone down).
The structure of bones, in conjunction with an adequate supply of calcium requires close cooperation between these two types of cells. It is a highly complex activity requiring several different hormones and signalling pathways to achieve proper rates of growth.
Throughout our lives these cells are constantly working to renew and repair the bones. At millions of different sites throughout the skeleton, bone destroying cells break down old bone and bone builder cells are responsible for making the new bone.
If there is an imbalance in the regulation of the two sub-processes of bone remodelling – bone resorption and bone formation – this can result in many metabolic bone diseases such as osteoporosis.