Bone

Cortical bone - hard outer layer Trabecular bone - spongy inner layer

Osteoblasts - create and replair new bone $\rightarrow$ become osteocytes Osteoclasts - breakdown old bone in response to PTH

• Normal bone in constant state of turnover and remodelling

Bone biomarkers

Alkaline phosphatase

• Specific to bone and liver usually
• Phosphatase involved in mineralisation - released by osteoblasts
• Released more in increased bone remodelling

Procollagen type 1N propeptide (P1NP)

• Synthesised by osteoblasts
• Low dinurnal and intra-individual variation, not affected by food
• Increased with increased osteoblast activity and v.v

Collagen cross-links (NTX, CTX)

• Cross-linking molecules are released with bone resorption - increased in peroids of high bone turnover - hyperthyroid, etc
• Dinural variation
• Do not predict bone density

Bone density T-scores

• -1 and above normal
• -1 to -2.5 osteopenia
• -2.5 and below osteoporosis