| [ Summary ] |
Mesenchymal stem cells differentiate to immature osteoblasts, which further differentiate to mature osteoblasts, and osteocytes are considered to be finally differentiated cells. In the transition of osteoblasts to osteocytes, immature osteoblasts are randomly embedded into woven bone, while mature osteoblasts are embedded into lamellar bone in a regular pattern. It is proposed that mature osteoblasts are regularly embedded into the bone matrix due to the inhibition of osteoblast function by osteocytes. Oxygen, nutrition, and survival signals are supplied to osteocytes through gap junctions and canaliculi, and interruption of this communication causes osteocyte death. The number of osteocytes decreases with aging and osteocyte death causes microfractures. Parathyroid hormone, bisphosphonate, calcitonin, and sex hormones inhibit osteoblast death as well as osteocyte death. |