Osteoblasts__B -> Osteocytes__S 0 -> Pre_Osteoblasts__P 0 -> Pre_Osteoblasts__P Pre_Osteoblasts__P -> Osteoblasts__B Pre_Osteoblasts__P -> 0 Osteoblasts__B -> 0 0 -> Osteoclasts__C Osteoclasts__C -> 0 Bone_volume__z -> 0 0 -> Bone_volume__z