Mechanics: Unit 2 Skeletal tissue (online) Flashcards
1
Q
What is bone composed of?
A
osteocytes
non-cellular component: collagen and ground substance
inorganic component: calcium phosphate crystals
2
Q
Describe collagen fibres
A
strong and flexible but don’t allow stretching
3
Q
Describe ground substance
A
jelly-like cement
weak
4
Q
What gives bone its hardness and rigidity?
A
inorganic component
5
Q
What makes up
a) 25-30%
b) 65-70%
of bone’s dry weight?
A
a) collagen
b) inorganic component
6
Q
Name the 2 types of bone
A
compact
cancellous
7
Q
Give another name for
a) compact bone
b) cancellous bone
A
a) cortical
b) spongy
8
Q
What does compact bone form?
A
outer layer of bone as it is a dense structure
9
Q
What does cancellous bone form?
A
inner part of short, flat and irregular bones
liner inner part of long bones + metaphyses + epiphyses
10
Q
What is the basic structural unit of
a) compact bone?
b) cancellous bone?
A
a) haversion system
b) trabecula
11
Q
Describe cancellous bone
A
mesh-like
spaces have red bone marrow
12
Q
How is a haversion system formed?
A
laminae form cylinders around haversion canal
13
Q
Where are osteocytes found?
A
in lacunae ( the spaces between laminae)
14
Q
What does a haversion canal contain?
A
blood vessels and nerve fibres
15
Q
Which structure links lacunae to the canal?
A
canaliculi
16
Q
What connects lamellae?
A
collagen fibres
17
Q
What structures
a) do
b) don’t
trabeculae have?
A
a) lamellae, lacunae, canaliculi
b) canals
18
Q
Which type of bone tissue contains haversian canals and why are they needed?
A
cortical bone
contain blood vessels which are needed to supply the bone tissue with nutrients
19
Q
What is a tensile load? + example
A
a load that acts to stretch a material like in a rope
eg radius and ulna when lifting an object
20
Q
What is a compressive load? + example
A
a load that acts to compress a material
eg vertebrae carrying upper body weight
21
Q
What is stress?
A
a measure of the concentration of a load
22
Q
How do we calculate stress?
A
force/area
23
Q
What are the units for stress?
A
n/m2
24
Q
What is strain?
A
a measure of the amount of deformation a material has undergone.
25
How do we calculate strain?
change in length/ original length
26
What does a strain-stress curve show?
how a material deforms as it is loaded
27
What are the 2 regions of the strain stress curve? and what separates them?
elastic region and plastic region
| separated by yield point
28
Describe the elastic region of the stress-strain curve
linear ie. stress is proportional to strain
| will return to original shape/size once load is removed
29
Describe the plastic region of the stress-strain curve
small inc in stress = large deformity
| will not return to original
30
What is Young's modulus?
ratio of stress to strain tells us how flexible or stiff a material is
31
What does a small young's modulus indicate?
material is flexible
32
What is a shearing force?
when two forces act in the opposite direction
33
Give an example of a shearing force
screw on fracture fixation plate
| bone cement by hip prosthesis
34
Is cortical bone stronger in shear, compression or tension?
compression then tension then shearing
35
Give an example of a fracture caused by shearing
intra-articular fracture of the femoral condyle
36
Give the two types of bending force and an example of each
cantilever ie. one side fixed eg. diving board
| 3 point eg seesaw
37
describe the sides of a bent structure
one elongated side due to tension
one compressed side
and a neutral axis with no distortion between the two
38
Along which surface will a fracture most likely occur when an excessive bending load is applied to a long bone?
elongated side
39
Describe a torsion load
twist along a longitudial axis ie. one side of bone fixed and one twisted
40
What type of fracture results from an excessive torsion load?
spiral fracture
41
When considering torsional loads, do hollow or solid bars have the best strength-to-weight ratio?
hollow
42
How do muscles affect stress distribution of bones?
attach via tendons and change the loads when they contract
43
Why is it sometimes desirable for muscles to contract even when it is not to produce movement?
muscles contract when bone subject to large tensile load to make the overall load compressive
this is because the bone is stronger in compression
44
What is Wolff's law?
bone is laid down where needed and resorbed where it is not
45
What affect does
a) exercise
b) inactivity
have on bone?
a) increases stress so bone lays down more collagen and minerals and is stronger
b) bone is resorbed causing bone atrophy
46
How does fracture fixation affect bone remodelling?
plates cause bone immobility and stress shielding ie they take most of the stress, this makes bone weaker
47
How do screws affect bone remodelling?
increase the stress causing hypertrophy
48
What is a fatigue/stress fracture?
fracture caused by a repeated application of a load that is smaller than the ultimate strength of the bone over a short period of time
49
Why are children prone to greenstick fractures but not adults?
their bones contain a greater proportion of collagen than adult bones which gives their bones a greater amount of flexibility
50
How would you recognise a greenstick fracture?
an incomplete fracture with one side bent and the other buckled
51
How is cancellous bone tissue affected by ageing?
affected more so than cortical bone
| thinning of the longitudinal trabeculae and the resorption of some transverse trabeculae
52
What age is bone lost quicker than it is made? What qualities does this change make?
35-40
| bone only loses a little strength but becomes a lot more brittle
53
What does cartilage consist of?
cartilage cells, fibres and ground substance
54
Name the 3 types of cartilage and give an example of each
hyaline eg articular, tip of nose
elastic eg external ear, epiglottis
fibrocartilage eg pubis symphysis, intervertebral discs
55
In what type of joints is articular cartilage found?
synovial eg hip and knee
56
What are the two main roles of articular cartilage?
to cushion the bones and to provide a smooth, lubricated, bearing surface.
57
What consistency is articular cartilage and what function does this provide?
firm but pliable means shock is absorbed evenly to reduce contact stress
58
What is articular cartilage composed of?
organic matrix of non-cellular material (collagen)
chondrocytes
interstitial fluid (water)
proteoglycans
59
What forms the organic matrix of non-cellular material in articular cartilage ?
collagen structures in strong fibrils
60
Where are proteoglycans found in articular cartilage?
middle zone
61
Where are chondrocytes most densely packed?
deep layer
62
what function do chondrocytes have?
they maintain, manufacture and secrete the organic matrix
63
How many layers (or zones) does articular cartilage have?
| Name them
3: superficial tangential, middle and deep
64
How is articular cartilage attached to bone?
the collagen fibrils that extend from the deep zone into the underlying bone tissue
65
how are collagen fibrils arranged in
a) superficial zone of articular cartilage?
b) deep zone of articular cartilage?
a) parallel sheets
| b) large bundles anchored perpendicular to bone
66
What shape are chondrocytes in
a) superficial layer?
b) middle layer?
c) deep layer?
a) oblong
b) circular
c) circular in columns
67
What does the tidemark in articular cartilage divide?
deep zone from calcified cartilage
68
How does articular cartilage behave mechanically
viscoelastic
69
What is the difference between creep and stress relaxation?
Creep is an increase in strain under a constant stress whilst stress relaxation is a reduction in stress under a constant strain.
70
Will viscoelastic material return to its original size and shape when a load is removed?
yes but not immediately
71
Why does stress relaxation occur in articular cartilage?
initially as fluid is forced out there is a large frictional drag that needs a large force to compress the tissue but then once fluid is all in the surface layer which is the most compacted the stress needed to compress it is decreased
72
Give the 3 types of lubrication
elastohydrodynamic
boosted
boundary
73
What is elastohydrodynamic lubrication?
when 2 surfaces, one of which is deformable, are lubricated by a film of fluid so that they do not touch
74
Summarise the differences between hydrodynamic and squeeze film lubrication in terms of when they occur
hydrodynamic: when surfaces slide over each other
squeeze film: when surfaces are forced together
75
describe boosted lubrication
as two surfaces are forced together the gap between them decreases and the resistance to lubricant is greater than the resistance of small molecules like water flowing through permeations into articular cartilage
so solvent of synovial fluid is lost and leave behind a viscose gel that can withstand the increased load
76
Which type of lubrication stops direct contact of articulating surfaces when large loads completely deplete the fluid film?
boundary
77
describe boundary lubrication
molecules in lubricant attach chemically to the surfaces to stop them touching when the fluid is depleted completely
78
which molecule allows for boundary lubrication in humans?
lubricin
79
What are tendons and ligaments?
dense and fibrous connective tissues
tendons connect muscles to bones
ligaments connect bone to bone
80
What are the cells in tendons and ligaments called?
fibroblasts
81
How are the collagen fibres arranged in tendons and ligaments? why?
In tendons collagen fibres are aligned in parallel and in ligaments collagen fibres are aligned nearly in parallel.
tendons have one large load in one direction but ligaments have this and also smaller loads in other directions
82
What is the basic mechanical behaviour of tendons and ligaments?
viscoelastic
83
What tensile properties must
a) a ligament
b) a tendon
withstand?
a) the forces that could split joints
| b) muscle contraction
84
What happens when a tensile load is applied to move tibia and femur apart?
ACL elongates up to 7mm before it fails
85
If the compressive load on a bone is doubled, how will the stress and strain be affected?
the stress doubles
| the strain doubles if it is in the linear elastic range
86
What happens to the distribution of pressure in elastohydrodynamic lubrication when we consider the surface as deformable not rigid?
distribution of pressure increases so the magnitude decreases and the film of fluid remains relatively thick
