Bone is not just an organ with a single supply of rejuvenating cells; it is a chimera of rejuvenation. It has at least two sources for two sites. There are growth-plate resident OCR (or OCHRE) cells, which form lengthening bone. They arise early in development and then gradually decay with age. And there are LR cells that arise later in adolescence and adulthood that participate in the maintenance of thickness of long bones, and bone fracture repair.
