Skeletal Tissue Flashcards
Name the 4 principle types of tissue in MSK?
epithelial
connective
muscle
nervous
Name 4 types of connective tissue
bone
articular cartilage
tendon
ligament
Which tissue is the most abundant in the body?
connective tissue
What is remarkable of connective tissues?
their ability to withstand repeated loading over multiple years
Name the 4 types of bones
long
short
flat
irregular
What are bone cells called?
osteocytes
What is the non-cellular organic component of bone made from?
strong collagen fibres in a jelly-like matrix called ground substance
Can collagen fibres be stretched?
no - but they are flexible
What is the inorganic component of bone made from?
calcium phosphate crystals deposited within the matrix
What substance gives bone its characteristic hardness and rigidity?
calcium phosphate crystals
What are the two types of bone tissue called?
compact (cortical)
cancellous (trabecular)
How does the quantity of compact bone vary between different areas of bones?
areas of high stress have a higher density of compact bone i.e. femoral shaft
How do cells in cancellous bone align themselves?
in line with directions that will best support the loadings
what is the basic structural unit of compact bone?
Haversian System
What is the basic structural component of cancellous bone?
Trabecula
Describe a Haversian System
They are arranged longitudinally in columns of around 200 micrometers in diameter.
in these units, the bone tissue is arranged in layers called lamellae forming concentric rings around a central canal - the Haversian canal.
This canal contains blood vessels and nerve fibres
Between the lamellae there are small cavities called lacunae that connect osteocytes.
Each osteocyte is links to others and the Haversian canal via cannaliculi - along which nutrients are carried.
Collagen fibres connect layers of lamellae.
Each haversian system is surrounded by ground substance - the weakest part of a bones microstructure.
Describe the structure of cancellous bone
a latticework of branching sheets and columns. Trabeculae are similar to Haversian systems except they do not contain Haversian canals. Haversian canals are not needed in cancellous bone as blood vessels pass through the marrow filled spaces between trabeculae, supplying nutrients to osteocytes through the canaliculi
Why does cancellous bone not need Haversian canals?
Blood vessels pass directly through the marrow filled spaces between trabeculae and supply osteocytes with nutrients via canaliculi
What happens to an object in tension?
it is being stretched like a rope
What happens to an object in compression?
a load is acting to compress the material
What is stress?
Force/cross-sectional area
What are the units for stress?
N m*-2
What is strain?
Change in length/oringinal length
How is strain expressed?
as a ratio
What is elastic behaviour?
if an object is not deformed beyond its yield point then it will resume its original shape on removal of the load
What is the boundary between the elastic region and the plastic region called?
yield point
What happens in the plastic region?
the bone yields to the applied load and for a mall increase in stress the bone deforms a lot. It will not recover its original shape and is permanently deformed.
What is the ultimate strength?
the point at which fracture will occur
What is young’s Modulus?
the relationship between stress and strain. Describes how stiff or flexible a material is
Name materials with a high young’s modulus.
What does this mean?
Diamond
A large amount of stress is required to produce a small strain.
Name a material with a low Young’s Modulus.
What does this mean?
Rubber
A small stress is required to produce a large strain i.e. it is flexible
What happens in shear loading?
two forces acting in opposite directions cause layers within the materials to slip or shear.
Under what type of loading is bone weakest?
Shear
Rank tension, shear and compression loading in order of bones ability to withstand stress
compression
tension
shear (lowest strength)
What are 2 types of bending?
cantilever
3 point
In cantilever bending, one side is compressed and the other is elongated, what happens in the middle?
neutral axis where no deformation occurs
Along which surface will a fracture most likely occur when an excessive bending force is applied to a long bone?
the side under tension
What is torsional loading?
When a bone is twisted about its longitudinal axis
What kind of fractures occur from torsional loading?
spiral fractures
In a structure subject to torsional loading, where is distortion greatest?
on the outer surface - the centre is a neutral axis.
How are long bones designed to withstand torsional loads effectively?
they are hollow with strong cortical bone making up the outer layer.
the hollow structure maximises their strength to weight ratio.
A bone of the same size completely solid, would greatly increase the weight with only a small increase in ability to resist stress
What is combined loading?
the presence of more than one type of loading
What influence does muscle activity have on bone stress?
Muscles can contract to alter the distribution of load on a long bone to prevent fracture by producing an overall compressive load where bone is stronger
What is Wolff’s law?
bone is laid down where it is needed and reabsorbed where not needed
What does bone do in response to the mechanical demands placed on it?
alters its size, shape and structure
What is it called where inactivity and lack of exercise leads to resorption of bone tissue?
bone atrophy
What is stress shielding?
Where bone weakness underneath a fixation plate as the plate absorbs all of the load on the limb. This is why plates should be removed as soon as possible
What is the name given to increase in bone tissue?
bone hypertrophy
How is a fatigue fracture caused?
A fatigue fracture occurs when the repetitions of an exercise are too frequent and happen quicker than bone can remodel to cope with the stress.
What begins to happen to bones around the ages of 35-40?
bone tissue resorption begins to exceed formation.
thinning of the trabeculae and loss of some transverse trabeculae = reduced cancellous bone
bones become slightly weaker and much more brittle
How are children more prone to greenstick fracture than adults?
Greater proportion of collagen in childrens bones mean they are more flexible.
greenstick fractures are incomplete fractures where one side is bent and one side is buckled
