Lecture 3 Flashcards
What are the 5 functions of bones?
- Support
- Leverage
- Protection of organs
- Storage of minerals and lipids (calcium)
- Blood cell production (red and white cells are produced in the red marrow)
Flat bones?
Scapula, sternum, cranium
Long bones?
Femur, humerus, tibia
Short bones?
Carpals, tarsals
Irregular bones?
Vertebrae, mandible
Sesamoid bones?
Patella
Sutural bones?
Small, flat irregular bones of the skull
Trabecular, cancellous or spongy bone?
- Network of trabecular struts
- Commonly found at the end (epiphyses) of long bones
Compact or cortical bone?
- Solid bone
- Forms the solid outer shell and shaft (diaphysis) of long bones
What are the two main components/phases of bone?
Organic phase:
- Type 1 collagen. Very pliable (easily bent
Inorganic phase:
- Calcium Hydroxyapatite crystals. Offer compressive strength to the bone
What is the composition of a bone?
- Bone material (inorganic)
- Collagen (organic)
- Water and ground substance
- Bone is a living tissue which has a blood supply and nerves
Osteoporosis?
A disease which compromises the matrix structure of bone, significantly reducing its mechanical strength.
Are vertebrae able to resist compression, tension and torsion associated with various movements?
They are able to resist compression, tension and torsion associated with various movements. This is in part due to the orientation of the trabeculae within the vertebrae.
What does the spine offer support for?
For the head, upper limbs and thoracic cage during movement and weight bearing activities
Femur?
The femur is a long, slightly curved, hollow (essentially) cylindrical shaped bone with compact bone around the centre of the shaft and trabecular bone at the ends.
What is the function/purpose of mechanosensing cells (osteocytes) in the body?
These cells detect changes in their physical and chemical surroundings and release chemicals in response causing bone to be removed or formed
Deformation?
Change fo shape
What does deformation depend on?
Depends not only on the size of the force but also the area over which the force is applied,
Force per Unit Area (N/m2
What are the three common types of stress applied to the bones and tissue within the human body
- unstressed object
- compression
- tension
- shear stress
Stress (action)?
The stress (σ) in a material with cross-sectional area (A) subjected to a force (F) is given by:
𝜎=𝐹/𝐴
Stress (reaction)?
- When a material of length (L) is subjected to a compressional or tensional stress, a change of length (ΔL) occurs. The resulting strain (Ɛ) is defined as the fractional change in length of the material (therefore Ɛ has no units).
- Measures the change un shape as a result of an action
𝜀=Δ𝐿/𝐿
Young’s modulus equation?
- Young’s Modulus (E) is the ratio (slope of graph) of Stress to Strain (Nm-2)
𝐸=𝜎/𝜀
Elastic region vs. Plastic deformation?
Elastic - bone will go back to original shape
Plastic - bone is permanently deformed
Tension?
In tension, bone undergoes less strain before reaching the yield point.
Compression?
Bone is stronger under compression
can withstand higher stress
Anisotropic material?
- What bone is
- Having a physical property which has a different value when measured in different directions
What does Young’s Modulus measure?
- Measure of stiffness or rigidity
High Young’s Modulus = Stiff material
When can you not measure Young’s Modulus?
On a curved line, bc it has to be linear
Bone bending?
- Hydrogen and covalent bonds hold bones together
- When bending a bone, you stretch and stress all of these bonds
When bending bone, where is the greatest change in length?
Along the surface, therefore the greatest resistance forces occur at the surface (Newton’s Third Law)
Neutral surface?
- When a bone is bending, the resistance forces decrease as you move towards the centre
- As you move from the outside of the bone (experiencing the most resistance/change in length) towards the inside of the bone, the change in length decreases, thus the resistance decreases until eventually there is no change of length/resistance…the neutral surface
Will there be more or less resistance to bending in a hollow or solid structure?
There will be more resistance to bending in a hallow structure, bc there isn’t any material in the centre (no bonds holding material together), therefore there is no change in length and no stress happening in the middle, so you’re only getting really big resistance forces and changes of length at the surface
When will resisting forces be the greatest?
When the material is distributed as far as possible from the neutral surface (hollow surfaces), but there must be a compromise, bc if the 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
What bone structures in the human body have an optimal biomechanical design due to their hollow nature with regards to bending?
- Femur
- Vertebrae
