LO: Describe the normal structure of bone and how it is maintained

Bone deformation

• Compression
• Tension
• Shear (torsion)
• Weight and gravity
• Muscles and tendons

Bone types

• Trabecular (spongey/cancellous) bone
  
• Corticol bone - hard

Composition of bone

• 22% organic: 90% Type I collagen, bone proteoglycan, cells
• 70% inorganic: Ca, P, Mg, Na, K
• 8% water

Bone cells

• Osteo - bone
• Osteoblast - formation
• Osteoclast - resorption
• Bone lining cell - protection and communication
• Osteocyte - communication
• Chondrocyte - bone growth

Bone remodelling

Activation

• Micro crack
• Deformation
• Osteocytes in bone
• Pre-ostoclasts - osteoclasts

Resorption

• Osteoclasts fuse with crack, breakdown of damage
• Osteoclast apoptosis
• Resorption cavity

Formation

• Osteoblasts release osteoid to fill in cavity with newly mineralised bone

Mineralisation

• Newly mineralised bone hardens and osteocytes embedded

Quiescence

• Bone resorbed - bone formed

Regulatory factors

• Bisphosphonates
• Sclerostin
• Oestrogen

Endochondral ossification

• Growth plates - long bones
• Grow from ends to centre - pushes bone out to grow
  

Intramembranous ossification

• Embryological development - flat bones

Bone imaging

DXA (DEXA) scan

• Diagnosis of osteoporosis
• Bone density

Peripheral Quantitative Computed Tomography (pQCT)

• Structure of bone
• Research tool

Techniques

• Bone biopsies and histomorphometry
• Caclification of osteoid
• Osteoblast, osteoclast and osteocyte number
• Trabecular connectivity

Biomarkers

• Pro-collagen 1 peptides - P1NP and P1CP
• Alkaline phosphatase
• Osteocalcin
• Collagen type 1 fibre components - telopeptides CTX/NTX