10: Articular Cartilage

types of cartilage

elastic, hyaline, fibrocartilage

elastic cartilage

protein: elastin
ex: epligottis, layrnx, ear
has the MOST ECM, very elastic!

hyaline

primary component of articular cartilage

fibrous cartilage

ex: has the LEAST ECM and MOST collagen
ex: IVD, pubic symphysis, meniscus

articular cartilage development begins to develop around the ___ week of gestation

5th

_______ stem cells producing cartilage are _______________

mesenchymal ; pluripotent

limb development is called what considering articular cartilage?

endochondral ossification

steps of limb development

1) cartilage scaffolding
2) chondrocytes form at the articular and transient cartilage and transient cartilage at the end of the opposing bones
3) chondrocytes undergo hypertrophic differentiation in the middle of the limb bud
4) limb bud layers mesenchyme over layer of ectodermal cells forming a ridge (AER)

AER

apical ectodermal ridge

AER has what 2 functions

1) allows the mesodermal cells to replicate
2) protects the cells allowing for limb growth

AER is controlled _ dimensionally... explain

3
proximal & distal
anterior & posterior
dorsal & ventral

zone of ________________________ - controls the anterior -> posterior (formation of the digits)

zone of polarizing activity

zone of polarizing activity is controlled from what gene

the sonic hedgehog gene

role of articular cartilage

covers articular surfaces (except TMJ)

4 functions of articular cartilage

1) distribute joint load over wider area (cushioning/shock absorption)
2) allow relative movement of the opposing joint surfaces with minimal friction
3) improve fit of articular surfaces
4) provide lubrication of articular surfaces

characteristics of articular cartilage

avascular
no lymph drainage
not innervated
very few cells (chrondrocytes)

main cells of articular cartilage

chondrocytes

chondrocytes make up less than ____-% of the tissue volume

10

role of chondrocytes

manufacture, secrete, organize, and maintain the organic component of ECM

matrix is composed of dense network collagen (type ?)

type II

how is collagen in articular cartilage distributed and layered

inhomogeneously distributed and layered

superficial zone of articular cartilage

densely packed fibers randomly woven in parallel planes to the articular cartilage

what % of weight is the superficial zone

85% of dry weight

superficial zone is the lowest concentration of

proteoglycans

superificial zone - resists ____ component of compressive load

tensile

middle zone of articular cartilage

greater distances between the collagen

middle zone - _____________ concentration of PG; _________ of cartilage

highest; workhorse

deep zone of articular cartilage

the fibers come together forming larger, radially oriented fiber bundles

deep zone - cross the _____________ insert on calcified cartilage and subchondral bone

tidemark

proteoglycan

protein polysaccharides with GAGs attached

aggrecans purpose

is to aid in structural stability

aggrecans have an affinity with ___________

hyaluronan molecules (hyluronic acid) --> attracts water

aging causes water content and car/protein ratio ______

decreases

water content in articular cartilage- what %

80%

what cations does articular cartilage contain

Na+ K+ Cl-

water in cartilage allows for ________

waste, gases, and nutrients to flow back and forth in the cartilage

how do materials move in articular cartilage

passive diffusion

the___________________ is crucial to joint lubrication

movement of water with loading

compressive loads lead to _________ controlled by PGs

deformation

fluid flows out of collagen, which leads to inc concentration of PGs, which leads to _________ negative charge, which leads to attracting _____ which ____the tissue

inc
water
stiffens

other ____________improve the structural ingrity and and provide additional stiffness

PGs (biglycan, decorin)

the compressive force will lead to little deformation or volume changes -->

cells are protected and no mechanical damage to the tissue is observed

the ability of PGs to resist compression comes from (2 things)

1) the donnan osmotic swelling pressure associated with the tightly packed anionic group
2) the bulk of stiffness of the collagen PG complex

weeping

fluid exudation under compressive loads

weeping causes loss of ____-% of original fluid content

50%

tissue is very ______ = the measure of ease with which fluid can flow through a porous material

permeable

permeability is inversely proportional to the _________ of fluid flow, implying how much force does it take to get fluid moving through tissue

frictional drag

permeability changes with changes in _______ and ______________ loading

magnitude and rate of compression

permeability decreases ______ while load increases and rate increases

exponentially

once yield is quickly reached, failure occurs _____ and fracture ________

quickly, patterns vary

toe region

small because it is not reflective of de-crimping (should be nonlinear)

elastic region

linear region (wavy)

plastic region

fracture point occurs very soon after plastic region is met

what are the 3 viscoelastic behaviors

creep
stress relaxation
hysteresis

the viscoelastic properties are all _____ than in tendon/ligament

less

takes _________to reach equilibrium on creep and stress relaxation

longer

over time fluid is redistributed and allows load to spread out over __________________________________

greater surface area

takes _______ for hysteresis to reduce but the area between the curves is not any bigger than ligament/tendon

more reps

during stress relaxation ...

weeping occurs initially followed by fluid redistribution

during creep....

only weeping appears to occur... takes hours to reach relative equilibrium point during creep and stress relaxation

rate of time dependent behaviors depend upon __________________

fluid exudation rate (related to the permeability of the tissue)

aligment of collagen along the axis of tension. there is a resistance of tension by the collagen strands = ?

articualr cartilage under tension

no change in volume=no intersititial fluid flow. collagen is responsible for the tension restriction = ?

articular cartilage under shear

biofilms

Colonies of bacteria that adhere together and adhere to environmental surfaces.

synovial fluid plays significant role in

lubrication

fluid film interaction

thin film of fluid that creates a surface separation like oiling

fluid film interaction probably develops as a result of ___________ of articular cartilage

weeping

part of the compressive load is supported by the pressure developed in the

fluid film layer

cartilage can carry _____ loads for _____ durations

high loads, short durations

fluid film lubrication

Movement increases the amount of fluid between articulating surfaces, thus increasing their separation

fluid film lubrication is the

first responder to compressive loads - especially fast rates of loading

over time the fluid film layer ______ with pressure application leaving high load areas _____________

thins out, unprotected

fluid film flayer is important for _________, but likely most important for ___________ as it allows nutrients in and out of articular cartilage

reducing friction
nutrition of articular cartilage

_____ is not as good as the boundary layer

coefficient of friction

boundary layer lubrication

considered a monolayer of lubrication directly on top of the articular cartilage

boundary layer consists of ________

hyaluronan

what is considered a concentrated fluid

boundary layer

boundary layer handles ____ loads, ____ speeds, ____ duration

high, low, long

boundary layer prevents _____________contact and eliminates most of the surface wear

surface to surface contact

boundary layer contains ______

independent physical properties of the lubricant and the bearing material only

boundary layer is dependent upon

chemical properties of the lubricant

boundary layer can reduce friction ______times

3-6

the boundary layer is the best ________ of all lubricating systems in the body

coefficienct of friction

both types of lubrication exist, and a shift occurs from ______ early on during activity to ____________ with sustained loading activity

fluid/film
boundary

the middle layer is the

working layer

injury leads to the __________ of random collagen fibrils

disruption

disruption causes more swelling pressure to expand the collagen network --> forms ________

vertical columns (instead of random)

injury disrupts the orientation of ____ and cells which lessen the mechanical strength of tissue

aggrecan

breakdown defined by volume of load being too high

single insult

breakdown defined by being applied too often

fatigue failure

both types of loading cause what?

unwanted removal of material from the articular cartilage by mechanical action occurring

during breakdown of articular cartilage, _____ is unable to keep up with these loads and cannot prevent tissue damage

lubrication

2 types of wearing

interfacial wearing
fatigue wear

interfacial wearing

interaction of surfaces related to friction

fatigue wear

related to deformation over time under load

interfacial wear has to do with what layer

superficial ; weight bearing surfaces come into direct contact with no lubrication

adhesions

pieces stick to each other and pull off original surface

abrasions

soft material is scraped by a harder one; leads to shredding

once injured, will adhesions or abrasions occur?

both

interfacial wear increases ________ and softening of cartilage

permeability