The role of the vitamin D endocrine system in avian bone biology.

The involvement of vitamin D and its endocrine system is essential, both for the process of bone development and growth, as well as bone remodeling. Important bone cells participating in those processes include the osteoblast (bone formation), the osteoclast (bone resorption) and the growth plate chondrocyte (longitudinal bone growth). The hormonally active form of vitamin D3, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], generates many of the biological responses attributed to the parent vitamin D3, including actions on osteoblasts and chondrocytes and the stimulation of the production of osteoclasts. 1,25(OH)2D3 is able to generate biological responses via both genomic and nongenomic pathways. This review provides a summary of this area.