FUNCTION OF BONES

1. FUNCTION OF BONES • 1. Support (body shape, structure, mass) • 2. Protection (brain, internal organs, marrow) • 3. Rigid levers (muscle force ---> torque) • lever: barlike body that can rotate around an axis

2. FUNCTION OF BONES • 4. Production of blood cells (red marrow), stem cells • platelets, erythrocytes (RBCs), leukocytes (WBCs) • * also bone cells, stem cells for heart

3. FUNCTION OF BONES • 5. Calcium storehouse • large Ca2+mineral deposits • reservoir to maintain blood [Ca2+] at 5 mEq

4. Bone is Dynamic! • • Hard (bone) and soft (tendons, ligaments, cartilage) have constant protein (and mineral) turnover - REMODELLING • • NET content a product of • > protein, mass gain • > protein, mass loss

5. BONE REMODELING • Bone remodeling • net content a reflection of both: > protein, mineral gain > protein, mineral loss • affected by mechanical stress, strain • hormones, prostaglandins, cytokines, nitric oxide

6. BONE CONSTRUCTION • Epiphysis – End of a bone. Separated from shaft epiphyseal plate (cartilage replaced by bone by adulthood) • Diaphysis – The shaft of a bone. • Articular Cartilage – slick hyaline cartilage on ends of bones - articulate w/ other bones.

7. articular cartilage Bone Construction (humerus)

8. Composition of bones by mass • 15-20% water • (helps - mechanical properties, nutrients, etc.) • 70 % minerals • (Ca2+ salts in crystal form - hydroxyapatite) • 5-10% organic • (cells, proteins like collagen)

9. How do bones detect mechanical stress and strain? • 1. ∆ in Charge distribution - piezoelectric • 2. Cytoskeleton (integrins, FAK, nitric oxide synthase) • 3. Nitric oxide synthase - produces •NO (nitric oxide) • cytoskeleton, blood vessels---> bone cell function • 4. Inflammation (prostaglandins) & Damage (micro, traumatic) • 5. Movement of blood, interstitial fluid (fluid shear) • • nitric oxide synthase • 6. Growth factors: IGF-1, TGF, VEGF

10. A. BONE MINERAL CONTENT • • 70% of bone mass • • form crystals called hydroxyapatite on protein matrix • > calcium phosphate • > calcium carbonate • Give bone its stiffness and strength • > especially compression, bending

11. B. NON-MINERAL BONE CONTENT(organic) • 1. water • • 15-20% of bone mass • • much in “gel-like” state • • allows diffusion of oxygen and nutrients • • increases ductility ( brittleness) • • interaction with proteoglycans and glycoproteins --> cement - stabilize bone • • mechanical stress & strain lead to “flow”or fluid shear past cell surfaces • (“mechanical action” while exercising)

12. BONE CELLS Osteoblasts – deposit new bone protein and minerals during growth & repair (remodelling) • small, oval shaped w/ single nucleus • receptors for hormones (ex. estrogen) • can detect mechanical stress or strain

13. BONE CELLS Osteoclasts – resorb old, damaged bone material • large, multinucleated cells • produced in red marrow, cousins of white blood cells • receptors for hormones (ex. estrogen)

14. Bone Remodeling Strong, healthy bone maintained through continuous bone remodeling. Two phases: resorption and formation. 1. Bone-resorbing cells (osteoclasts) remove old bone by releasing acids, enzymes, reactive species to remove minerals and collagen. 2. Once osteoclasts complete resorption, protein-secreting cells (osteoblasts) deposit new bone tissue.

16. http://www.youtube.com/watch?v=yENNqRJ2mu0 Repeated dynamic stress causes bone to remodel Source: National Geographic REMODELLING

17. BONE CELLS Osteocytes – Mature osteoblasts that have been trapped by bone material - help supervise function of osteoblasts & osteoclasts • projectiles detect the mechanical, chemical, and hormonal environment chemicals inflammation hormones stress growth factors microtrauma