The major factors that stimulate osteoblasts to make new bone, however, may be peptide growth factors that are actually stored within the bone matrix and released as a consequence of bone resorption. These peptide growth factors include transforming growth factor b (TGF-b), the bone morphogenetic proteins and the insulin-like growth factors.
The cellular events of bone remodelling are highly co-ordinated so that a balance usually exists between the processes of bone formation and bone resorption. When an imbalance occurs between bone formation and bone resorption, such as with ageing, there is usually more bone lost by the activity of osteoclasts than can be replaced by the activity of osteoblasts.
