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HUB3006F > Tendons > Flashcards

Tendons Flashcards

1
Q

What is a tendon?

A

A range of morphologically diverse structures that connect muscle to bone

Transmits force created within the muscle to the bone

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2
Q

What are the 2 categories of musculoskeletal injuries?

A
  1. Acute injuries:
    o Single macro traumatic event in which the tissue is acutely overloaded and fails
  2. Chronic (overuse) injuries:
    o Tissue eventually becomes painful when it is subjected to multiple repetitive stresses that it is not able to withstand.
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3
Q

What are the common causes of musculoskeletal injuries?

A
  1. Participating in physical activity

2. Specific activities in the workplace

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4
Q

What is tendon rupture?

A

Acute tendon injury

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5
Q

What is Tendinopathy?

A

Chronic overuse injury

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6
Q

What is the Iceberg Theory?

A
  • Model of Tendinopathy pathogenesis
  • Has 3 stages
  1. Healthy exercise -> healthy load (within physiological range)
    o Net increase in collagen synthesis
    o Tendons becomes larger, stronger, more injury resistance
    o Increased tensile strength & elastic stiffness
2.	Relative Overload -> micro ruptures
	o	Collagen fibers begin to:
		-	Slide past one another
		-	Break at crosslinks
		-	Causing tissue denaturation
	o	Cumulative microtrauma
  1. ECM Degradation
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7
Q

What is the Tendon Pathology Continuum Model?

A
  • Model of Tendinopathy pathogenesis
  • Has 2 stages
  1. An appropriate load within a physiological range lead to positive adaptation (e.g. increased proteoglycan production)
    o Called reactive tendinopathy
    o Is reversible if load is reduced
  2. If load exceeds healthy levels -> matric/collagen disruption by increased PG’s -> opportunity for vascular growth
    o Tendon disrepair
    o Not reversible
    o Can lead to degenerative tendinopathy
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8
Q

What are 2 models of tendinopathy pathology?

A
  1. The iceberg Theory

2. The Tendon Pathology Continuum Model

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9
Q

What are the predominant causes of chronic tendinopathy?

A
  1. Collagen disarray and degeneration
  2. Fiber disorientation and thinning
  3. Increased ground substance (Aggrecan)
  4. Neovascularization
  5. Areas of increased or decreased prominent of tenocytes
  6. Failed healing response
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10
Q

What are the mechanical properties of Tendons?

A
  1. Non-linear
  2. Viscoelastic:
    a. Has both elastic & viscous properties
    b. When force 1st applied, it stretches and returns to original length (elastic).
    c. If force is continually applied, it stops returning to original length (viscous)
  3. Anisotropic:
    a. Properties are directionally dependent
  4. Heterogeneous:
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11
Q

What is the general makeup of tendons?

A
  • ± 2/3 of tissue = water (Not liquid, bound in collagen structure)
  • 1/3 is tightly packed parallel bundles of predominately Type I Collagen fibrils
  • Fibrils aggregate into larger structural units  tendon
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12
Q

What is the hierarchical structure of a tendon?

A
  1. Collagen molecule
  2. Collagen fibril
    a. Smallest structural unit
  3. Collagen Fiber
    a. Endotenon: thin layer of loos connective tissue that surrounds the fiber which also has tenocytes
    b. Tenocyte: cells that make up the tendon
  4. Fascicle
    a. Innervated and has blood vessel supply
  5. Tendon
    a. Surrounded by peritendon (Paratenon & Epitenon)
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13
Q

What are the structural components of a tendon?

A 
-	Extracellular Matrix:
	o	Ground Substance:
		a. 	Proteoglycans (PG's)
		b.	Glycosaminoglycans (GAGs)
		c.	Inorganic components
	o 	Protein Fibers:
		a. 	Collagen
		b.	Elastin
	o	Non-fiber Proteins:
		a.	Glycoproteins
-	Cells:
	o	Tenocytes
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14
Q

What is the Extracellular Matrix?

A
  • Part of any tissue in the body
  • Proteins + ground substance
  • Space that surrounds the cell
  • Much higher amount of ECM in tendons than in other tissues
  • Is produced and maintained by cells (e.g. fibroblasts)
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15
Q

What are glycoproteins? And what are their role in tendons?

A
  • Non-fiber proteins, part of ECM
  • Don’t form fibers
  • Variety of shapes and functions & sizes:
    o Adhesive proteins: act as cement, holding fibers and cells together
    o Regulatory cell-matrix interactions:
    a. Repair & adaptation
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16
Q

What is Ground Substance?

A
  • Saline gel-like medium in which the protein fibers and cells are embedded
  • Consisting of:
    o Water (60-80% total weight)
    a. Therefore highly hydrophilic
    o Maj. Macromolecular components:
    a. Proteoglycans
    b. Glycosaminoglycans (GAGs)
17
Q

What does Ground Substances contribute to?

A 
-	Contributes to:
	o	Lubrication
	o	Protection
	o	Diffusion of mols & metabolites
	o	Strength & elasticity
18
Q

What is the basic structure of Proteoglycans?

A
  • Forms a highly hydrated, gel like substance, in which fibrous proteins are embedded
  • Basic structure:
    o Core protein
    o Carbohydrate chains = glycosaminoglycans
19
Q

Aggrecan

A

o Large hyalectan Proteoglycan

o Has lots of GAG’s so will bind lots of water – so lots in tissues that need to withstand lots of compressor forces

20
Q

What are Glycosaminoglycans?

A
  • Long unbranched (linear) polysaccharide chains formed from repeating disaccharide units
  • Disaccharide unit sugars:
    o Uronic acid
    o Either N-acetylglucosamine or N-acetylgalactosamine
  • 1 or both sugars contain sulphate groups (negative charge)
    o Therefore GAGs are HIGHLY negatively charged
    o Therefore they bind water – giving it resistance to deformation
21
Q

What is a Tenocyte?

A

Mature tendon cell – maintains tissue

22
Q

What is a Tenoblast?

A

Immature, synthetically active cell

23
Q

What are integrins?

A
  • Cell surface receptors
  • Part outside cell can bind to matrix
  • Part inside can bind to cytoskeletal components
    o Resulting in a physical link between ECM & cell
  • Any force applied to the matrix can be transmitted through integrins & cytoskeleton into the cell
  • Mechanical loading triggers fibers in the matrix to stretch
  • This stimulates the cell through the integrins
  • Cell-cell communication
  • The cell responds through protein synthesis
24
Q

What is Collagen?

A
  • Family of 28 proteins defined by structural component of amino acids not function
    o Therefore family has very diverse functions
  • Building blocks of several connective tissues
  • Type I fibril = basic building blocks of tendons, ligaments, bones
  • Type II fibril = basic building blocks of cartilage
25
Q

Describe Collagen alpha-chains

A
  • The basic structural unit of the collagens
  • Consists of repeating uninterrupted (1 repeating unit) or interrupted (>1 unit) Gly-X-Y sequence
  • 3 alpha-chains form a left handed triple helix
  • Every 3rd amino acid = glycine:
    o Gly has simplest side chain (-H)  allows it to twist gently into chain
  • X is often proline and Y is often hydroxyproline (Add -OH)
  • Some lysin residues are also hydroxylated
  • Molecule is glycosylated
26
Q

Type I Collagen

A

o Major fibrillar collagen in bone, tendon, ligament, muscle
o Most abundant type
o Confers rigidity
o Heterotrimer: 2x alpha-1 chains; and 1x alpha-2 chain

27
Q

Type II Collagen

A

o Major fibrillar collagen in cartilage and fibrocartilage

o Homotrimer

28
Q

Type III Collagen

A

o Frequently found with Type I
o Forms reticular fibers which crosslink to form a fine meshwork
o Confers elasticity
- Changing collagen type (e.g. from Type I to III) can change properties of tissue
o Found particularly in tissues with elastic property (blood vessels, lungs etc.)
o Homotrimer

29
Q

How are collagen fibrils formed (Type I)?

A
  1. Alpha-chains produced from cellular mRNA -> wrap into triple helix
  2. Triple helix starts where Gly-X-Y sequence starts and continues till it ends
  3. This forms Procollagen – ‘pro-‘ means it’s a precursor to collagen that must be cleaved
    a. Has a collagen domain AND 2 globular domains on either end
  4. Procollagen is exported out of cell and the globular domains are cleaved -> collagen
30
Q

How are fibrils assembled?

A
  • Fibrillogenesis:
    o Assembly of collagen molecules to form fibrils
  • The quarter-staggered array:
    o The last ¾ of the top molecule aligns with the 1st ¾ of the next molecule
  • Originally non-covalent interactions hold the molecules together
  • Over time they are replaced by covalent interactions
  • Lysyl oxidase forms covalent crosslinks between lysine and hydroxylysine
    o Crosslinks important for tensile strength, energy absorption & resistance to proteases
31
Q

What are the stages of the Tendon Stress-Strain Curve?

A
  1. 0-1% stretch = crimping. The crimps straightening out
  2. 1-3% stretch = Physiological region:
    o Elastic properties, will return to original length
    o Straight line graph of stress vs strain %
  3. 3-5% stretch = partial ruptures:
    o Microtrauma – intermolecular cross-links start to fail
  4. 5-8% stretch = overuse /chronic injury:
  5. > 8% stretch = Tendon rupture

HUB3006F (8 decks)

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