Bone

90% of protein in bone is type I collagen

Type I collagen is also the major structural protein in tendons and skin

Calcium in bone turns over 100% per year in infants

Calcium in bone turns over 18% per year in adults

Bone resorption by osteoclasts

--> New bone formation by osteoblasts

Cycle takes ~ 100days

Renewal rate for bone

4% per year for compact bones

20% per year for trabecular bones

PTH accelerates bone resorption

Oestrogen slows bone resorption
* Inhibition of cytokines (e.g. IL-1, IL-6, TNF-alpha) which stimulates osteoclasts
* Stimulates TGF-beta which increase apoptosis of osteoclasts