Tendon Organisation

Question 1

Describe the hierarchical arrangement of collagen

Answer 1

Tropocollagen –> microfibril –> Fibril –> Fascicle –> tendon

Question 2

What is another name for microfibril

Answer 2

Pentafibril (groups of 5 collagen molecules bind together by intramolecular cross links)

Question 3

What results in the banding pattern seen in collagen fibrils?

Answer 3

Longitudinal arrangement of the collagen triple helices

In a quarter stagger pattern

Gaps of 40nm between the ends of each molecule

Question 4

What is critical for tendon mechanical strength?

Answer 4

The mediated assembly and cross-linking of collagen into microfibrils

This process depends on extracellular SLRPs which dictate overall thickness and quality of fibril assembly.

Question 5

Why are tendon fibrils crimped?

Answer 5

due to specific orientations of the microfibrils.

Question 6

What is the purpose of tendon crimping?

Answer 6

Contributes important mechanical properties

When extended stiffens and transfers force of muscle to skeleton efficiently, while remaining not stiff the rest of the time.

Question 7

Are tendon fascicles visible with the naked eye?

Answer 7

yes

Question 8

What is another name for endotenon?

Answer 8

Intrafascicular matrix

Question 9

What is endotenon?

Answer 9

A thin connective tissue layer separating and binding together the fascicles

Question 10

What type of tendon is the endotenon especially important for?

Answer 10

those that act as energy stores

Question 11

What is an epitenon?

Answer 11

Layer of connective tissue continuous with the endotenon, envelopes entire tendon

Question 12

What is the purpose of the endotenon and epitenon?

Answer 12

Permeate the tendon with vasculature, lymphatics, and nerves

Question 13

What is the paratenon

Answer 13

An additional loose connective tissue layer that surrounds the tendons in regions away from joints (e.g. Achilles)

Question 14

What is the purpose of the paratenon?

Answer 14

Facilitates movement of tendons below the skin

Question 15

What is a synovial sheath?

Answer 15

Covers other tendon which pass around a joint (e.g. flexor tendons) to ensure smooth gliding past surrounding structures

Question 16

What does the presence of a paratenon vs a synovial sheath depend on?

Answer 16

degree of gliding required

Question 17

Where is the ground substance found?

Answer 17

At each level of the hierarchy collagen

Ground substance = highly hydrated matrix

Question 18

What are fibre composits?

Answer 18

Materials with an arrangement of stiff fibres within a surrounding, softer matrix

Question 19

How do fibre composites stretch?

Answer 19

through a combination of extension of and shearing (sliding) between the fibrous components.

Question 20

What do the contributions of extension and shearing in fibre composite stretching depend on?

Answer 20

the mechanical properties of the fibres and surrounding matrix.

Question 21

What is the myotendinous junction?

Answer 21

Transition from muscle to tendon is abrupt rather than gradual (compared to enthesis)

Question 22

Describe the structure of the myotendinous junction

Answer 22

Composed of interdigitations of the end sarcomeres and connective tissue elements

Z-line (staggered organisation with next sarcomere) gives rise to myofilament bundles that insert directly onto collagen fibrils.

Question 23

Why do tendon collagen fibres and sarcolemma interdigitate via fingerlike projections?

Answer 23

to increase interface area

This arrangement minimizes stress to the myotendinous junction with forceful contractions

Question 24

What are myotendinous junctions prone to?

Answer 24

injury

Question 25

What is the enthesis?

Answer 25

Bone-tendon junction

Question 26

What are the two types of enthesises?

Answer 26

Indirect and direct

Question 27

What is a name for indirect insertion?

Answer 27

fibrous

Question 28

What is a name for direct insertion

Answer 28

fibrocartilagenous

Question 29

Describe the structure of fibrocartilagenous insertion

Answer 29

More complex than indirect - Four-layer transition from tendon to bone: Zone 1: Tendon Proper Zone 2: Fibrocartilage Zone 3: Mineralized fibrocartilage Zone 4: Bone

Question 30

Describe zone 2 of direct insertion

Answer 30

Rich in associated proteins including type II collagen and proteoglycans

Question 31

Describe zone 3 of direct insertion

Answer 31

Type X collagen (associated with endochondral ossification) Varying amount of bone mineral

Question 32

Where are direct insertions found?

Answer 32

in regions where tendon-bone unit is subject to high tensile loads (e.g. rotator cuff)

Question 33

Which kind of insertion is more common?

Answer 33

direct

Question 34

Describe fibrous insertions

Answer 34

Tendon fibres insert directly into the periosteum (metaphysis or epiphysis of a long bone) Have Sharpey fibres

Question 35

What are sharpey fibres?

Answer 35

Fibers that interdigitate with the periosteal tissue

Question 36

where are indirect insertions common?

Answer 36

Common in areas where tensile loading at the tendinous insertion does NOT predominate (e.g. distal head of rectus femoris)

Question 37

What is the tendon blood supply like?

Answer 37

hypovascular Fed primarily by vasculature that enters through the paratenon or bony insertions and continues through the endotenon

Question 38

What is the blood supply in sheathed tendons like?

Answer 38

Blood supply must enter via mesotenon in vincula

Question 39

What are vincula

Answer 39

A band of connective tissue, similar to a ligament, that connect a flexor tendon to a phalanx bone

Question 40

Other than blood supply where else do tendons get nutrition from?

Answer 40

Diffusion through synovial fluid

Question 41

What are avascular zones at higher risk for?

Answer 41

Ruptures (eg. Achilles)