Hormonal factors: PTH, Insulin, Glucocorticoids, Vitamin D.
Growth Factors: see below.
Bone Morphogenetic Proteins (BMPs)
in the TGF-b family, effects on many cells, induce ectopic endochondral ossification.
Coupling of Resorption and Formation
As OCs break down the bone cytokines that were trapped in the matrix get released (matricrine) and activate OBs.
But how do the OBs know where to act? Some lysosomal enzymes released by OCs have mannose-6-phosphate sugar residues on them. These enzymes now coat the newly destroyed surface. The receptors on the OB cells mistake these residues for IGF molecules, bind them, and proceed with their action.