- Bone matrix- haversian system are made up of collagen fibres and Ca phosphate salts, containing blood vessels
- Bone Cells- osteoclasts (destroy old bone tissue), osteoblasts (create new bone matric), osteocytes (former osteoblasts- controlling/signalling function
What is bone remodelling?
- bone reabsobed (osteoclasts)
- new bone formation (osteoblasts)
- bone may or may not change its density and thickness
- purpose: repair micro damage; supply calcium to serum
in adults- equilibrium; in
in children- formation > resorbtion
Aging- bone loss accentuated (resorbtion> formation)
How is bone remodelling controlled?
- mechanical stress (weight bearing or mm contraction); osteoblastic vs osteoclastic activity
- hormones: lengthening via growth plate- growth hormone and sex hormone: parathyroid hormone or cortisol
- RANK ligand
What is local tissue signalling factors?
- rank ligand- RANKL- a regulatory cytokine expressed by osteoblasts. It bins to RANK receptor on osteoclast and activates them. RANKL overproduction> degenerative bone disease
-osteoprotegerin- OPG- a glycoprotein decoy receptor to which RANKL binds and thereby prevents RANKL binding to RANK
- bone remodelling
How does bone grow?
- chondrocytes (produce cartilage)
- osteoblasts (produce bone matric and facilitate its mineralization
- action of GH on bone is indirect, via IGF-1. By binding to its specific recptor, IGF- 1 causes mitogenic effects in chondrocytes (hypertrophy and proliferation), activated osteoblasts and inhibits of osteoclasts.