Connective Tissue Physiology Flashcards
connective tissues
fibrous connective tissue, adipose tissue, cartilage, bone, blood
functions of connective tissue
binds: ligaments (bone to bone) and tendons (muscle to bone)
supports: framework for organs and body as a whole (bone)
protects: protection against external environment and repairs (adipose)
insulates: adipose
transports substances: wastes and nutrients
major site of stored energy: adipose tissue (fatty acid can be mobilized and become pre-fatty acid and used as a big source of energy)
mesenchyme
precursore cell/origin
-blast
premature form of connective tissue that will differentiate into a -cyte
-cyte
mature form of connective tissue cells
can connective tissue cells de-differentiate?
yes!
mobilization=differentiation
immobilization=de-differentiate
3 primary germ layers
ectoderm, mesoderm, and endoderm
ectoderm
outer germ layer
nerve tissue
mesoderm
middle germ layer
muscle and connective tissue
endoderm
inner germ layer
inner lining of digestive system
what layer(s) do(es) epithelial tissue (mesenchymal cells) come from?
all 3 germ layers (ectoderm, mesoderm, and endoderm)
aging tissues
thinning epithelia
less effective tissue repair
tissue atrophy (smaller thinner mass)-osteoporosis
DNA mutation (greater cancer risk)
cartilage doesn’t repair well (even when young)
tendons
parallel arrangement
lower metabolism (limited vasculature=longer healing)
muscle to bone
unidirectional tension
less type 3 and more type 1 collagen than ligaments
- greater dynamic capabilities
- has to resist greater tensile force
has tendon sheath (tenosynovium)
- mostly type 3 collagen (cushion)
- protects tendon from friction
functions:
- shock absorption: dissipates forces from muscle to bone
- stabilize joints (compression or restriction of translation)
- contributes to length-tension relationship and maintaining optimal muscle length (stretched muscle can generate more force)
ligaments
interlaced arrangement
- densely packed fibers in multiple directions
fibers in line with tensile forces
greater metabolism (has vasculature)
bone to bone
most often joint surfaces
heterozygous:
- 10-20% cells (mainly fibroblasts)
- 80-90% ECM
–> mostly type 1 collagen (high tensile strength) and some type 3
–> amount of elastin=very little stretch
functions: mechanical stability, guide and restrain movement, prevents unnecessary translation by compressing joint surfaces
ligaments and tendons have an active or passive role in motion?
passive
myotendinous junctions
where muscles meet tendons
interdigitation b/w collagen fibers and muscles
-reduced load/immobilization=flatter and decreased=decreased function of transmitting tensile forces
–> start with low load/resistance
very sensitive to mechanical condition
function: transmitting/ dissipating tensile force from muscle to bone
entheses
insertion area for joint capsule, ligaments, and tendons on bone
direct attachment
via fibrocartilage
common site for degenerative change
perpendicular to bone=more likely a direct insertion
indirect attachment
via fibrous attachment
blend into periosteum (outer bone)
Sharpey’s fibers serve as “roots”
parallel to bones=more likely indirect insertion
direct insertion zones
zone 1: end of tendon/ligament
zone 2: uncalcified fibrocartilage
zone 3: calcified fibrocartilage
zone 4: merge into cortical bone
tidemark differentiates bone and fibrocartilage
ligament and tendon immobilization
water loss=shrinking
random arrangement of fibers
stiffer tissues=break easier w/little stress
stress
amount of force imparted on tissue
strain
amount of deformation of tissue upon stress
stiffness
ability to resist deformation (strain) when stress is applied
compliance
opposite of stiffness
tissue can be easily changed
stress strain curve
shows relationship b/w stress and strain as a curve
curve changes depending on material of tissue
- increased cross sectional area= thicker=stiffer=more vertical curve
- longer tissue=more compliant=more horizontal curve
toe region
initiation of the force
beginning of fibril stretch
elastic region
linear relationship b/w stress and strain
tissue returns to normal length when the stress is removed
normal day-to-day activities
yield point
some ruptures in some fibers begin
plastic region
microfailure of collagen fibers trigger synthesis of new components
no return to normal length when stress is removed
Therapeutic region
some pain, but no surgery required
ultimate stress/stress
beyond this point=rupture/fracture
macrofailure
macrofailure
complete failure of all tissues
tendon vs ligament stress strain curve
- tendon: more vertical=stiffer bc of more type 1 collagen (high tensile strength)
- ligament: more horizontal=more compliant
viscoelasticity
viscocity: resistance to deformation/flow
- honey=high
- water=low
- depends on proteoglycans and water composition
- time dependent: increase/decrease w/time
- rate and temp dependent: increase temp=decreased viscocity, slow load= decreased viscocity
elasticity:
- ability to return to og length/shape after removal of load
- depends on collagen and elastin content and organization
time and rate dependent properties
creep and stress-relaxation
creep
CONTINUED DEFORMATION of tissues over time with CONSTANT STRESS after initial elastic response has occurred
gradual return to shape once stress is removed
clinical: stretching shortened muscle-exert constant force and over time will feel less resistance
stress-relaxation
when tissue is stretched to FIXED LENGTH (CONSTANT STRAIN), the stress required to maintain the length decreases over time
feeling of resistance lessens over time
fast loading
increased creep and stress relaxation
stiff muscles (larger force needed to deform the tissues)
more vertical curve
hysteresis
when viscoelastic material is loaded/unloaded, the unloading curve is different from the loading curve.
the difference b/w the 2 curves=energy dissipated (usually heat)=decreased viscocity
as tissue changes length and is heated w/repeated stretches, higher loads are tolerated in subsequent reps
failure load (ultimate stress) increases giving more wiggle room b4 rupture which makes the exercises safer
factors that affect mechanical behavior
maturation and aging
- maturation: increased collagen=stiffer=can resist increased stress w/less strain
-aging: decreased collagen=more brittle=more susceptible to stress
pregnancy and postpartum
- increased laxity
mobilization/immobilization
- mobilization: stronger and stiffer w/stress
–> exercise increases tensile strength
- immobilization: decreased tensile strength=break with less stress
functions of articular cartilage
produce smooth, lubricious surface for decreased friction
transfer load to subchondral bone
nutrition of articular cartilage
avascular: relies on diffusion of synovial fluid for its nutrient supply and waste removal
compression=efflux
NWB=influx
no influx/efflux=no waste removal/nutrients incoming
to maintain cartilage health, you need to exercise for repetitive compression and relaxation
cartilage responses to compression
reduces cartilage volume and increases pressure=efflux of interstitial fluid
eventually the stress balances the applies load
thicker=more resistance to compression
responses to tension
dif zones behave dif
- stiffer in superficial (tangential) zone
responses to shear
no volume changes=no interstitial fluid flow
higher collagen=lower friction
types of cartilage growth
interstitial growth and appositional growth
interstitial growth
growth within
growth through mitotic division of existing chondrocytes (new matrix made within cartilage)
occurs in immature cartilage (high tissue mass at epiphyseal plates and articular surfaces)
appositional growth
growth on the surface
new cartilage laid down at the surface of perichondrium (chondroblasts for ECM and develop into mature chondrocytes)
occurs in mature cartilage
articular cartilage degeneration
magnitude of stresses
duration of stresses
changes in molecular and microscopic structures:
- loss of superficial cartilage fibers=increased permeability=lost fluid
changes in mechanical properties:
- lose ability to resist forces
interfacial wear of cartilage
bearing surfaces in direct contact
increased permeability, decreased lubrication
occurs in damaged/degenerated joints
fatigue wear of cartilage
low loads over long period
impact loading
rapid application of high loads
insufficient time for interstitial fluid redistribution to relieve the compacted region
opposite of fatigue wear
endochondral ossification
not degeneration
replacement of calcified layer of articular cartilage
maturation/growth
aging
calcification occurs w/in chondroid
aging of cartilage
abnormal mechanical stresses and inflammatory cytokines
thinning of superficial cartilage
- osteoarthritis: repetitive or high loads causing thinning of superficial layer of cartilage)
articular cartilage repair/regeneration
little to no repair capacity upon injury
depends on interstitial growth (division of chondryocytes w/in cartilage) and ability of chondrocytes to synthesize and maintain ECM
aging cartilage is even more limited in ability to repair
