Lecture 19 - Bones

• support • protection from mechanical trauma • sites of muscle attachment via tendons • movement • site of blood cell formation - bone metabolically active [white blood cells] • fat storage - yellow bone marrow • calcium and phosphorous reserve - maintain minerals

• bone is made of cells and extra cellular matrix (ECM). Cells inside the ECM in concentric circles • there are two types of cells: • osteoblasts - produces new bone tissues • osteoclasts - digests bone tissue • ECM is made of inorganic matter [50% hydroxyapatite and organic matter 25% collagen matter and the remaining 25% is water] note: collagen holds the bone together

• the concurrent process of new bone tissue for formation and digestion of existing bone is called bone remodelling • it helps to reshape bone in response to mechanical loading and also repair bone following fractures • Calcitonin, dietary Ca2+, mechanical stress, oestrogen in females promote bone formation • the lack of these and parathyroid hormone promote bone resorption (bone breakdown)

Compact Bone • Dense (porosity 5-10%) • Makes up 80% of total bone weight • Provides strength yet lightweight Spongy Bone • Porosity greater than 70% • Found in shaft and around surfaces • Capability to accommodate RBM and YBM

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the bone is an anisotropic material which means it responses to load changes depending on direction of load.

• The playing arm of professional tennis players have cortical thicknesses 35% greater than the opposing arm • Astronauts experience bone density loss following space flight (decreased loading) • Weight lifters develop thickening of the bone at the insertion of active muscles, where stress applied is greatest

Tension - bone pulled from different sides, by pulling tendons e.g. marathon running could result in transverse fractures Compression - likely to occur in fast bowlers for cricket. Landing on a single foot causing hairline fractures. it is an oblique movement Bending - Likely to occur in football or rugby tackles - this is where the bone bends but does not break. it causes a BUTTERFLY FRACTURE Torsion - It is twisting of the bone, can happen in any sport that involves changing direction in a short space of time

DIRECT - injury at the site of force application INDIRECT (avulsion fractures) - bone ie pulled out from insertion site by a tendon or a ligament

Osteo-necrosis - Death of bone cells resutling from cessation of blood flow (interruption in blood flow due to long term steriod use, excessive alcohol intake, radiation therapy Osteo-porosis - Decrease in bone mineral density - more susceptible to fractures in the bones. Need to ensure enough calcium in diet and Physical activity [functions as a stimulus to maintain or increase bone density]

• Regular physical activity • Adequate supply of > Calcium > Phosphorous > Vit C, D, K • DEXA scans to help show which part of the bones are weaker