bone structure and elastic properties of biological material Flashcards
what are the 6 functions of bone?
-support
-locomotion - joints
-protection of organs eg skull, ribs, vertebral column
-storage of minerals eg calcium
-nourishment - eg teeth breaking food
-sound transmission - eg ossicles in the middle ear
what are osteocytes?
bone cells that are responsible for the maintenance of the bony matrix
what is bone remodelling?
a continuous process of destroying old bone and building new bone
-carried out by osteoclasts (bone destroyers) and osteoblasts (bone builders)
what 2 important materials are in bone?
-collagen - gives bone elastic properties
-bone mineral- inorganic material
compare how easily ‘bendable’ collagen vs bone mineral is
-collagen - like rubber and very pliable - easily bent
-bone mineral is very fragile and can easily be crushed with finger
what are 5 different categories of bone according to their shape & give examples ?
-flat - plate like bones - eg scapula
-long - humerus , femur etc
-cylindrical bones eg vertebrae
-irregular shaped function specific joint bones eg wrist, ankle
-others eg ribs
what are the 2 different types off bone ?
-compact or solid bone
-spongy or trabecular bone
where is trabecular bone found?
-commonly found at the end of the long bones eg femur
why is there trabecular bone at the end of bones?
- can reduce impact force as the trabecular bone are resistant to compression
-light and not as dense and heavy
why is the femur hollow?
as it provides maximum strength for minimal weight
what do all materials undergo after a stress is applied to them?
they will undergo some deformation (ie change of shape)
what does the deformation of the material depend on?
the force per unit area
what is the formula related to stress in a material with cross sectional area A subjected to a force F?
stress (theta symbol) = F/A
what are the units of stress?
newtons per square meter
N/m^2
what are the 3 common types of stress applied to bone and tissues within the human body?
-compression
-tension
-shear stress
what is compression force ?
compression force is when something is being pressed or squeezed together
what is a tension force ?
-tension is the opposite of compression force
-it occurs when something is being stretched or pulled apart
-eg rubber band being pulled apart
what is a shearing force ?
-shearing force happens when 2 surfaces slide past one another in opposite directions
-eg like a scissor movement
what is a rotational stress?
- occurs when a force is applied to the bone in a twisting or rotating motion
eg common in activities that involve sudden changes in direction eg basketball
what happens when a material of length L is subjected to a compressional or tensional stress?
a change of length occurs - called STRAIN
what is star defined as?
the fractional change in length of the material
does strain have units?
no
how are stress & strain related - on graph?
-graph - y axis is stress and x axis is strain
- graph is a straight line up until point A- ie if you double the stress, you will double the strain
- A= the linear limit
-between the point A and B - increasing the stress still increases the strain more, but not linearly related
-point C = maximum strength
-point D = fracture point
what is the elastic region on the stress / strain graph?
in this area of the graph, if stress is applied to the material, the material will still be able to go back to its OG shape and size once the stress is removed
what law does the elastic region of the stress . strain curve follow?
Hookes law (stress = young modulus x strain)
what is the plastic deformation area of the stress / strain curve ?
- region of the curve where the material undergoes non linear deformation that is permanent ie it docent return to OG shape or size
what is young Modulus (E) defined as?
-ratio of stress to strain
-it is a measure of stiffness or rigidity of a material
-it is the slope of the stress / strain graph in the linear region
what does a smaller vs larger value of young modulus mean?
-smaller value = more elastic material
-larger value = more stiff material
what is an important point to note about bone and its elastic properties under compression vs tension stress?
-bone is more elastic under compression than it is under tension - ie slope is smaller for compression than tension
-ie lower youngs modulus
what is anisotropy?
-a material behaves differently depending on which direction you’re looking at or measuring it from. It’s like having a material that’s stronger or weaker depending on which way you try to stretch, squash, or do anything to it.
-this happens due to its make up
what is a greenstick fracture?
-fracture resulting from direct trauma
-incomplete fracture of a long bone eg radius or ulna with one side of the bone intact and the other is bent
why do greenstick fractures happen?
as bone is more elastic and stronger under compression than under tension
what factors determine how a material can resist bending?
-material composition -youngs modulus - measure of how stiff a material is
-crosss sectional shape and size
take a simple shaped object eg a cylinder… what happens when we bend it - think of top and bottom surfaces and forces applied to it?
-top surface is under tension and the intermolecular forces are tying to pull the surface back to its OG shape
-bottom surface is under compression and the intermolecular forces are trying to push the surface back into its OG shape
what is the surface in between the top and bottom surfaces of th cylinder that is being bent?
the neutral surface - which undergoes no change in length
where do the resisting intermolecular forces increase?
the further they are from the neutral surface
why do tendons not have the same stress strain curve as bone?
- they exhibit non linear behaviour at stresses well below their elastic limit
-due to presence of collagen fibres
describe the type of bone in a vertebrae
- body consists of a cylinder of cancellous bone w/ trabeuculae surrounded by a thin layer of cortical bone
what forces are vertebrae able to resist & why ?
compressional, tensional and torsional
-due to the orientation of the trabecular within the vertebrae
the femur is a long, hollow cylindrical shaped bone with compact bone around the centre of the shaft and trabecular bone at the ends… why?
- heads of the bone - trabecular - will act as shock absorbers
-trabecular bone is also resistant to compressional and tensional stresses
-also compact bone in centre to provide max strength to bone
