Bone - Biological Properties and Remodelling
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What are (3) functions of bone?
• Calcium regulation • Mechanical support and locomotion • Protection of vital organs
What is the general composition of bone?
• Protein - organic osteoid matrix (25%) • Mineral (75%) • Cells (osteoblasts/clasts, lining cells, osteocytes, bone marrow)
What makes up the organic (osteoid) protein matrix and what is its purpose?
Mainly type 1 collagen, allows for flexible + tensile strength.
What is osteogenesis imperfecta?
AKA brittle bone disease - to do with genetic defect in type I collagen. Predisposes to bone fractures throughout skeleton.
What makes up the mineral part (75%) of bone? Why do we need mineralisation?
Hydroxyapatite (hydrated calcium and phosphate), function is to make bone rigid and brittle - for high compressional strength.
What happens in osteomalacia and osteoporosis in terms of mineralisation and bone quantity?
• Osteomalacia - not all of bone is mineralised (due to lack of Vit D), about 50% mineralised • Osteoporosis - Correct amount (80%) mineralised but lower bone quantity
What are the differences between trabecular and cortical bone?
• Trabecular • lower density • high SA • high remodelling rate • struts + plates • Cortical • higher density • low SA • low remodelling rate • haversian systems
Do we find osteoblasts and osteoclasts in trabecular bone or cortical bone?
Trabecular bone - very metabolically active.
What do osteocytes do?
Important as mechanoreceptors, talk to osteoblasts/clasts. Important in bone turnover.
Osteoblasts synthesise matrix proteins and form bone material. What type of cell are they derived from?
Derived from mesenchymal stem cells
How do osteoclasts resorb bone?
• Produce acid for dissolution of mineral • Produce proteolytic enzymes for digestion of matrix • Transcellular removal of calcium/phosphate/matrix - pathogen like cells
How does menopause lead to decrease bone mass in women?
Menopause -> less oestrogen Ostrogen is important for decreasing bone resorption, so without the oestrogen you have increased bone resorption, can even cause osteoporosis.
How is Pagets disease different from osteoporosis?
Pagets is localised problem in bone cells whereas osteoporosis is generalised.
What is Paget’s disease?
Overactive osteoblasts and osteoclasts resulting in weak bone resulting in deformaties.
When does a fracture occur?
Fracture occurs when force exceeds bone’s strength. Bone’s have good compressional and tensile strength but weak torsional (twisting) strength.
What does stage 1/3 of fracture healing involve?
• Macrophages remove debris • Granulation tissue • Fibrous tissue - vascularised
What does stage 2/3 of fracture healing involve?
Have to somehow reform bone • Osteoblasts produce soft callus (type1 coll matrix) • Woven bone (hard callus) formed by mineralisation - woven means it’s not organised
What does stage 3/3 of fracture healing involve?
Can take months • Lamellar bone formation and remodelling