3 - Tissue Mechanics and Injury

Question 1

What is the definition of a tissue?

Answer 1

It is an aggregate of cells that have a similar structure and function

Question 2

What are the 4 types of tissues?

Answer 2

Connective Tissue
Epithelial Tissue
Muscle Tissue
Nervous Tissue

Question 3

What is another name for connective tissue?

Answer 3

Inert Tissue

Question 4

True or false: all joints in the body are made up of connective tissue?

Answer 4

True

Question 5

What are some examples of connective tissue?

Answer 5

Bones, Bursae, Capsules, Cartilage, Discs, Meniscus, Ligaments, Tendons

Question 6

What is the extracellular matrix (ECM)?

Answer 6

It attracts and binds water, supporting substances for fibrous and cellular components
Contributes to the overall strength of the connective tissue

Question 7

What are the different components of the ECM?

Answer 7

Fibrous component (collagen and elastin)
Collagen Type 1
Collagen Type 2

Question 8

What is collagen?

Answer 8

a white fibrous tissue with steel-like strength. It is very rigid

Question 9

What is elastin?

Answer 9

It is a yellow fibrous tissue with elastic properties

Question 10

What is collagen type 1?

Answer 10

Thick fibers with little elongation

They resist tensile forces quite well

Question 11

What is collagen type 2?

Answer 11

thinner less stiff fibers, they resist compression and shear forces

Question 12

What makes up the cellular component of tissues?

Answer 12

Resident cells and circulating cells

Question 13

What are resident cells?

Answer 13

Depends on what type of tissue they are in but they are cells that are always present
Examples: Fibroblasts (collagen) Osteoblasts (bone) and Chondroblasts (cartilage)

Question 14

What are circulating cells?

Answer 14

They appear when a tissue is inflamed or damaged

Question 15

What are some examples of circulating cells?

Answer 15

Lymphocytes

Macrophages

Question 16

What is the ECM to Cell component ratio in ligaments?

Answer 16

Cells make up 10-20%

ECM makes up 80-90%

Question 17

What is the make up of a ligament? Like what type of fibers is it composed of?

Answer 17

Primarily Type 1 Collagen fibers
They are densely packed
Arranged in the line with the applied tensile force (may have varying directions of the ligament depending on the direction of the force ex. MCL)

Question 18

What is the ECM to Cell component ratio in tendons?

Answer 18

Similar to ligaments, 10-20% cells and 80-90% ECM

Question 19

What is the make up of a tendon? Like what type of fibers is it composed of?

Answer 19

Has more type 1 collagen fibers than ligaments as it has to withstand stronger tensile forces
Its fibers are aligned in one direction

Question 20

What is the fibrocartilaginous junction?

Answer 20

It is the gradual change in tendon structure which is divided into 4 zones.
It diffuses the load at the tissue-bone interface to help prevent injury

Question 21

What are the four zones of the fibrocartilaginous junction?

Answer 21

Zone 1 - Tendon
Zone 2 - Uncalcified fibrocartilage
Zone 3 - Calcified fibrocartilage
Zone 4 - Bone

Question 22

What is the musculotendinous junction?

Answer 22

It is where muscles intertwine with the tendon

It is very sensitive to mechanical conditions and becomes flatter with low load

Question 23

What is hyaline cartilage?

Answer 23

It is composed of type 2 collagen and compresses the proteoglycan molecules that hold onto water during loading
It also lines articulating bones and distinguishes synovial joints
It is avascular and gets nutrients with compression

Question 24

What are the three zones of articular cartilage?

Answer 24

Zone 1 - parallel fibers, smooth, reduced friction, distribute forces
Zone 2 - mesh like to hold water and helps absorb compression forces
Zone 3 - Perpendicular fibers to zone 1, it securely holds the calcified cartilage

Question 25

What are the features of fibrocartilage?

Answer 25

Mostly type 1 collagen fibers. has a limited blood supply and relies on compression for nutrient diffusion.

Question 26

What are the features of bones

Answer 26

Primarily type 1 collagen. Supplied by calcium Has 2 layers: cancellous (spongy) and compact (cortical) Has both osteoblasts (lay down new bone) and osteoclasts (break down bone)

Question 27

What are the different types of loads you can place on a tissue?

Answer 27

``` Compression Tension Bending (tension and compression) Torsion Shear ```

Question 28

True or false: only some connective tissues are viscoelastic?

Answer 28

False, ALL connective tissues are viscoelastic

Question 29

What is creep?

Answer 29

A continuous change in shape with prolonged force application

Question 30

What is stress relaxation?

Answer 30

a tissue is stretched to a fixed length and held constant; the force needed to maintain that length reduces over time

Question 31

What is strain-rate sensitivity?

Answer 31

That more force is required to deform a tissue rapidly versus slowly

Question 32

True or false: cortical bone withstands greater force with less deformation than cancellous bone?

Answer 32

True

Question 33

True or false: the amount of strain required to reach failure is more in cortical bone than cancellous bone?

Answer 33

False it is less in cortical bone

Question 34

What defines a stress fracture?

Answer 34

Frequent loading of low magnitude

Question 35

What can lead to complete failure of bone?

Answer 35

A single load of high magnitude

Question 36

What determines the amount of force that a tendon can resist and the amount of elongation it can undergo?

Answer 36

It's cross sectional area, material and tendon length

Question 37

What does continuous compression do to tendons?

Answer 37

It modifies the composition to more resemble cartilage. It creates a shift from type 1 collagen to type 2 reducing its tensile strength resistance

Question 38

How do you increase thickness and strength of a ligament?

Answer 38

By loading it with intermittent tensile loads

Question 39

What three things does cartilage have to do to resist load?

Answer 39

Stress developed in the fibrillar portion of the ECM Swelling pressures developed in the interstitial fluid Frictional drag resulting from fluid flow through the ECM

Question 40

A contractile unit is also known as a ______?

Answer 40

Sarcomere

Question 41

What starts the cross bridge cycle?

Answer 41

An action potential releases Ca2+ and that exposes the binding sites between actin and myosin

Question 42

How is active tension developed?

Answer 42

By the active contractile elements of the muscle

Question 43

What are the factors that affect if more cross bridges form or not?

Answer 43

Frequency of motor unit firing Number of motor units firing Size of motor units firing Diameter of the axon

Question 44

How is passive tension developed?

Answer 44

By the non-contractile components of the muscle

Question 45

What are the parallel elastic components that help contribute to the tension

Answer 45

Epimysium Perimysium Endomysium

Question 46

What are the series elastic components of passive tension?

Answer 46

Tendons (when the muscle is stretched the tendon is pulled as well)

Question 47

True or false: there is a direct relationship between the tension development and the muscle length?

Answer 47

True

Question 48

What does optimal length mean?

Answer 48

Means the muscle is capable of developing a maximal tension