L.3 - bones Flashcards
What are the 5 functions of bone?
- Support
- Framework for attachment of soft tissue and organs. - Leverage
- Bones function as levers that can change the magnitude and direction of force is generated by skeletal muscles. - Protection of organs
- skull, ribs, spine. - Storage of minerals and lipids
- calcium (the parathyroid gland releases hormones which cause bones to release calcium) - Blood cell production
- red and white blood cells are produced in the red marrow
How many bones are there in the adult human Skelton?
- 206
In how many broad categories can the 206 bones of the body be categorized? State them.
- 6 categories
- Flat bones
- Long bones
- Short bones
- Irregular bones
- Sesamoid bones
- Sutural bones
Give examples of flat bones?
- scapula
- sternum
- cranium
Give examples of long bones?
- femur
- humerus
- tibia
Give examples of short bones?
- carpals
- tarsals
Give examples of irregular bones?
- vertebrae
- mandible
Give examples of sesamoid bones?
- patella
Give examples of structural bones?
- small, flat, and irregular bones of the skull
What are the 2 types of bones?
Compact or cortical bone - solid bone
• forms the sold outer shell and shaft (diaphysis) of long bones)
Trabecular, cancellous, or spongy bone - network of trabecular struts
• commonly found at the end (epiphyses) of long bones
What are the 2 phases of bone composition?
Organic phase and inorganic phase
What are in the organic and inorganic phases on bone composition?
Organic
• type 1 collagen - in bone. like rubber (very pliable - easily bent)
• collagen - 25% of weight of bone
Inorganic
• calcium hydroxyapatite- crystals that offer compressive strength to the bone
• bone mineral - 60% of weight of bone
Water & ground substance is also part of bone composition !!!!!!
What is a bone?
- a living tissue which has a blood supply and nerves
What cells are distributed throughout the bone(bone cells)?
- mechanosensing cells called osteocytes
What are osteocytes and what do the do?
- bone cells
- these cells detect changes in their physical and chemical surroundings and release chemicals in response causing bone to removed or formed
What will happen to materials when force is applied?
- deformation (change of shape)
What does deformation depend on?
- size of the force
- area over which the force is applied
Force per Unit area (N/m^2)
What is the equation of force/stress on a material?
sigma symbol = F/A
Sigma symbol = stress in a material
A= cross sectional area
F = force
What are the 3 common types of stress applied to the bones and tissues within the human body?
- compression
- tension (stretching)
- shear stress
What is a strain (reaction)?
- when a material of length (L) is subjected to compressional or tension so stress, a change of length (🔺L) occurs.
- the resulting strain (ع) is defined as the fractional change in length of the material (therefore ع has no units)
What is elastic deformation?
- within the elastic region of the graph (up to point B) deformation is elastic and the material will still red your to its original shape when the force is removed.
What is Young’s Modulus? What is the equation?
- symbol = E
- is the ratio of stress to strain (Nm^-2)
- is the slope of the stress-strain graph in the linear region up to point A
- it is a measure of stiffness or rigidity.
E = o / ع
Ratio of stress to strain = stress / strain
What does high Young’s Modulus indicate?
- stiff material
For small values of stress and strain (up to point a) the graph is a straight line which means …?
- strain is linearly proportional to stress
- material obeys Hooke’s Law (F ~ 🔺L)
What does Young’s Modulus tell us?
- for the same value of stress:
- Material #2 will undergo a greater strain (change in length) than material #1
- Material #2 is more elastic than material #1
What is plastic deformation?
- for all stress beyond point B (yield point), the material will be permanently deformed.
- point ‘C’ corresponds to the max permissible stress. Beyond this, the material is destined to fracture.
- point ‘D’ is the fracture point (ultimate yeild)
- all deformation in the range from B to D is said to be plastic deformation.
Bone in compression Vs tensions
Compression
• bone is stronger under compression (that means it can withstand higher stress)
Tension
• bone undergoes less strain before reaching the yeild point
What is young’s module for bone?
~ 17 • 10^9 Pa
Bone is what type of material?
Anisotropic
What influences both the stiffness and the ultimate strength of the bone?
- the orientation of the load application
- the orientations are longitudinal, tilted 30 degrees, tilted 60 degrees, and transverse.
What are the approx values which bone fractures fractures make occur?
Ultimate compressive strength:
20 x 10^7 Nm^-2
Ultimate tensile strength:
15 x 10^7 Nm^-2
Stress-strain characteristics VS tendon, skin, and other musculoskeletal connective tissues characteristics?
- bone exhibits well-defined stress-strain characteristics
- Tendon, skin, and other musculoskeletal connective tissues exhibit non-linear behaviour at stresses well below their elastic limit
Strength of neanderthal femoral cross section VS human femoral cross section?
- neanderthal femoral : could bear much more weight in compression.
- human femoral : more bendable
What are forces (bonds) found in bending bones?
- hydrogen bonds & covalent cross links hold bone constituents together.
What happens to bending bonds during bending?
- the bonds are strained and they revisit the change in length taking place (Newtons Third Law)
Where does the greatest changes in length occur in bending bones? What does this indicate?
- occur in the compression and tension surfaces.
- Therefore, the greatest resisting forces occur at the surfaces.
- these resisting forces decreases as you move towards the centre.
- at the centre, there is a surface which undergoes no change in length and experiences no resisting forces (neutral surface)
Resistance in a solid Vs hollow bone?
- solid: resisting forces increase in magnitude moving from the centre (neutral surface)
- hollow: only largest resisting forces as no material in the centre
You will have more resistance to bending in a hollow tube than a solid structure
When will resisting forces be greatest?
- when the material is distributed as far as possible from the neutral surface
What is the bone available material is spread too far from the neutral surface?
- the walls will become too thin and there is a danger that the structure will buckle under compression. Therefore, you must reach a compromise.
What type of bones have a natural curvature?
- most long bones such as the femur
Which bone would be stronger under compression: straight column bone or a curved bone?
- a straight column bone
When the load is increased, what will happen to the curved bone?
- it will bend more
What will happen to the long bone when loaded in the longitudinal direction?
- the bone will deform in a predictable direction
What is a femur?
- a long, slightly curved, hollow cylindrical shaped bone with compact bone around the centre of the shaft and trabecular bone at the ends
What does the spine support?
- the head, upper limbs, and thoracic cage during movement and weight bearing activities
How many vertebraes does the spine consist of?
- 33
- each has a complex structure offering max load bearing support
What does the vertebral body consist of?
- a thin layer of cortical bone (tube) syringing a cylinder of cancellous bone (shock absorber)
What are vertebrae able to resist?
- compression, tension, and torsion associated with various movements. This is in part due for the orientation of the trabeculae within the vertebrae
Look at slide 30 for diagram & memorize
!!!
What is osteoporosis? (Look at slide 31 for diagram)
- a disease which compromises the matrix structure of bone, significantly reducing its mechanical strength.
