TENDONS Flashcards
what are the types of connective tissue
- muscle
2.bone - tendons - muscle to bone
- cartilage
- ligaments -connect bone to cone
what are the 2 types of musculoskeletal injuries(bone, muscle, tendons and ligaments)
- acute onset injuries- from a single overuse event
- chronic overuse injuries - repetitive overuse
what is the point of union between muscle and tendon
the myotendinous junction
what is the point of union between muscle and bone
the osteotendinous junction
what are the 2 properties of tendons
they are viscous and elastic
what are features of the viscoelastic tendon material
- hysteresis
- rate dependence
- creep
- load relaxation
what is hysteresis
this is when the loading an unloading of a tendon leads to energy loss as heat
what is rate dependence
this is when the faster we load a tendon leads to greater stress and strain compared to when it is loaded slower
what is load relaxation
this is when a constant load is applied to tendons kept at constant length we see a decrease in the force in the tendons
what is creep
when a constant load is applied to tendons we see their length deform over time
explain the stages of the tendon stress(load) strain(elongation) curve
1.the first step is the toe phase where we see uncrimpling of the collagen fibres
2. linear phase where we see the collagen backbone straightening aswell
3. failure where we see the fibres sliding past one another and crosslinks breaking and so the the tendons fail
=rupture if not healed properly
what is the structure of a tendon
- collagen molecule(proteins ie type 1)
- fibril-protein collagen molecules come together
- fibre-fibrils come together
- fascicle -fibers come together
5.tendon-fascicles come together
what is the smallest structural unit of collagen
the collagen fibril
what are the collagen proteins made of
alpha chain triple helices
-these are when 3 alpha chains come together to form a helix
-each alpha chain is made up of triplet repeats of GLY-X-Y
-X is usually lysine or proline
-Y is usually hydroxylysine or hydroxyproline
-the triple helices are glycosylated
what are the types of fibrillar collagens
- type 1 collagen - 2a 1 and 1a2 chains
-most abundant type
-heterotrimer
-confers rigidity - type 11 collagen- 3a1 chains
-homotrimer
-most common in cartilage
3.type 111 collagen
- 3a1 chains
-often found with type 1
-confers elasticity
what are the collagen types found in bone, tendons, muscle and ligaments
major: type 1 and 3
minor: type v
what are the collagen types found in cartilage
major: type 2
minor: type XI
how does a type 1 collagen molecule form
- 3 alpha helices come together
- to form a procollagen
- then procollagen peptidase will cleave off the loose ends to form collagen
how do we go from a collagen molecule to a collagen fibril
the collagen molecules will align in parallel and form crosslinks for tensile strength to form a fibril
-the crosslinks form between lysine residues and hydroxylysine
what are FACITS
non fibrillar collagen with interrupted triple helices
-these support the fibrillar collagens
-the FACIT types in bone, ligaments, tendons and muscle is types XIV and XII
-the main FACIT type is IX in cartilage
what is the function of FACITs
they mediate the connection between collagen fibres and cell surfaces and they stabilise the fibrillar collagens
what are the components of tendons
- proteins
2.ground substance - cells
what are the proteins found in tendons
- fibrillar proteins- elastin and collagen(60-80%)
2.non fibrillar proteins -glycoproteins
what is in the ground substance found in tendons
- water
- glycosaminoglycans
3.proteoglycans
what cells are found in the tendons
- tenoblasts
2.tenocytes( tendon fibroblast) - fibroblasts
what are glycoproteins
they are the non fibrillar proteins in tendons and they function in providing adhesion of cells to cells and cells to the ECM
what does the ground substance contribute to in tendons
- lubricance
- adhesion
- protective barrier
- strength and elasticity
what do proteoglycans do
they have a core protein with GAGs protruding off
-they secrete the gel like medium of the ECM in which the fibres are embedded
what do glycosaminoglycans do
they also secrete the gel like substance of the ECM
that embeds the fibers
-they are made of repeating disaccharides(sugars) that have negatively charged sulphate groups making GAGs negatively charged
thus; can bind to water to give it its gel like properties
what are large hyalectan proteoglycans
- versican
- aggrecan
- they help with load bearing properties
what is the function of the fibroblasts and tenocytes in the tendons
they produce all the components of the ECM ie; the collagen fibrils; the ground substance components etc..
explain the steps of how collagen is formed from a tenocyte
- alpha chain mRNA
2.this translates into alpha chain protein - then the alpha chain lysine and proline residues are hydroxylated
- the chain is glycosylated
- then the helix forms
- the helix is then secreted into the ECM
- then the procollagen is cleaved by procollagen peptidase to generate collagen
- the collagen molecules then come together in parallel forming cross links to form a fibril
how do tenocytes respond to force placed on a tendon
the force/mechanical trigger stimulates the integrin receptor on the membrane
-this activates the cell
-cell to cell contact
-produce and release new proteins into the ECM
- this can be a healing process or an adaptation
achilles tendon injuries risk factors
- INTRINSIC RISK FACTORS
-previous injury
-flexibility
-weight
2.EXTRINSIC FACTORS
- shoes
-training method
-occupation
-physical activity
what is the iceberg theory used to explain
tendinopathy pathogenesis
explain the first step of the iceberg theory: healthy load
when a healthy load is placed on a tendon it is not harmful but instead re-inforces the tendon by stimulating the production of new collagen fibers. the tendon increases in elastic stiffness and tensile strength as it becomes larger, stronger and more resistant to injury
explain the second step of the iceberg theory:overload
this is when the tendon is overloaded or overused then the collagen fibres are going to begin sliding past one another; causing the crosslinks to break and thus; failure of the tendon. this microtrauma also impacts the rest of the ECM
what would be the tip of the iceberg in the iceberg theory
pain
explain the third step of the iceberg theory: healing
the optimal conditions for good healing is optimal recovery time and rest without more overloading. if this is not met could lead to rupture
-remember every person has different intrinsic and extrinsic factors so they will respond differently to healing and overloading so it needs to be specific for each individual
