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LS2Lect19bone

LS2Lect19bone - Life Sciences 2 Musculoskeletal growth and...

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Life Sciences 2 October 20 , 20 10 Musculoskeletal growth and development Readings: Chap. 16 Professor Daniel E. Lieberman Office hours Tuesday 2-3 Peabody 53 and by appointment : [email protected]
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TODAY: The “problem” of the skeletal system Why have bones? How do bones function and change while growing? Bone structure Bone growth & adaptability Other connective tissues Osteoporosis FRIDAY: how it grows along with the rest of the body…
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Why have bones? Function #1 PROVIDE STIFFNESS! = resistance to deformation Oppose gravity Permit muscles to generate movement Protect organs (e.g. brain, thorax) ouch!
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ε = Strain ( L/L) σ =Stress (F/A)* Stiffness, E = slope of stress vs strain (y/x) AKA Modulus of Elasticity (or Young’s modulus) f y ε f ε y σ y σ f elastic plastic y = yield f = fracture *unit = Pascals (N/m 2 ) What is stiffness? y x
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Strain ( L/L) Stress (F/A) very stiff very flexible intermediate
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To stay stiff, bone must also be strong Stress to generate plastic deformation: σ y Stress to generate fracture: σ f Strain ( L/L) weaker stronger Strength = resistance to deformation or fracture σ =Stress (F/A) f y σ y σ f f y Function #2: be strong
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99% of body’s calcium in bone Function #3: store calcium
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Haematopoesis (in bone marrow) Function #4: make blood cells
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Function #5: permit muscle to generate movement at joints
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These functions pose an interesting problem: How do you stay stiff, strong, permit movement, store calcium & make blood while changing in size and shape?
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A thought experiment: How would you “grow” a robot while enabling the robot to function during growth? How would you enable its structure to change as its functions changed? Evolution’s answer = bone A stiff, strong, dynamic tissue that is highly modifiable Imagine you had to design a robot to G R O W
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The “problem” of the skeletal system Why have bones? How do bones function and change while growing? Bone structure Other connective tissues Bone growth & adaptability Osteoporosis
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To the naked eye (macrostructurally) there are two types of bone Compact (cortical) vs. Trabecular (spongy / cancellous)
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All made of the same tissue Bone = two phase substance – Organic: Collagen Mineral: Calcium phosphate – Also some H 2 O + NCPs (non-collagenous proteins)
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