Physiology 3 Flashcards
how are synovial joints supported?
extra-articular structures
- ligaments
- tendons
- bursors
give 2 functions of joints
structural support
purposeful movement
give roles of joints in movement
distribute stress (often through muscles over joint)
confer stability via shape, ligaments and synovial fluid
joint lubrication
- cartilage interstitial fluid
- synovium derived hyaluronic acid
- synovium derived lubricin
how does a joint confer stability?
shape of articular component
ligaments
synovial fluid (acts as adhesive seal that permits sliding motion)
what are the functions of synovial fluid?
- lubricates joint
- facilitates movement by reducing friction
- minimises wear and tear via lubrication
- aids nutrition of articular cartilage
- supplies chondrocytes (cartilage cells) with O2 and nutrients and removes CO2 and waste products
how much synovial fluid is in the knee?
<3.5 ml
is synovial fluid static?
no
continuously replenished by synovial membrane
is synovial fluid thin or viscous?
viscous
due to presence of hyaluronic acid (mucin) produced by synovial cells
is synovial fluid always the same?
no
viscosity and elasticity varies with joint movement
rapid movement = decreased viscosity and increased elasticity
where are constituents of synovial fluid derived from?
dialysis of blood plasma
how many cells are contained within synovial fluid?
only a few
mainly mononuclear leucocytes
what changes occur in synovial fluid in osteoarthritis?
the ability of synovial fluid to change viscosity and elasticity is defective
what does synovial fluid look like?
clear and colourless
high viscosity
what is the cell count of synovial fluid?
<200/mm3 WBC
- polymorphs make up <25/mm3
WBC count will increase in inflammatory and septic arthritis
when can synovial fluid be red?
traumatic synovial tap
haemorrhagic arthritis
how does clarity/colour of synovial fluid change in septic arthritis?
becomes opaque due to high number of WBCs
variable colour
less viscous
what does articular cartilage do?
mainly prevents wear and tear of joints by providing low friction, lubricated gliding surface
distributes pressure to bone
what determines the mechanical properties of articular cartilage?
determined by composition of ECM and interaction between solid and fluid phase of cartilage
what are the zones of articular cartilage?
superficial
middle (biggest)
deep
calcified
how do zones of articular cartilage differ?
organization of collagen fibres and relative content of cartilage components
what type of cartilage is articular cartilage?
hyaline
what properties of articular cartilage have?
elastic
sponge-like
what are the components of articular cartilage?
special ECM made of water, collagen (mostly type 2) and proteoglycans
what is the function of water in cartilage?
maintains resiliency of tissue and contributes to nutrition and lubrication
70% of cartilage net weight (unevenly distributed)
what is the function of collagen in cartilage?
provides tensile strength and stiffness and maintains architecture
20% of cartilage net weight (mainly type 2)
what is the function of proteoglycans in cartilage?
compressive properties associated with weight bearing
10% of cartilage weight
what are proteoglycans composed of and where are they found?
glycosaminoglycan
highest concentration in middle and deep zone of cartilage
what happens to cartilage components with age?
they all decrease with age
what makes up most of the total cartilage volume in the body?
ECM (98%)
what maintains the ECM?
chondrocytes
they synthesise, organise and degrade
how do articular cartilage cells receive nutrients and O2?
articular cartilage is avascular so they get nutrients from synovial fluid
how do the rates of ECM degradation and synthesis match up?
degradation never exceeds synthesis
how do chondrocytes break down ECM components?
metalloproteinse proteolytic enzymes
- collagenase
- stromelysin
how does ageing affect articular cartilage?
changes in relative amounts of the 3 components of cartilage changes the mechanical properties of the cartilage
how might ECM cause joint disease?
if rate of ECM degredation exceeds synthesis rate
what are the catabolic factors of cartilage matrix turnover and what do they do?
TNF alpha, IL-1
stimulate proteolytic enzymes and inhibit proteoglycan synthesis
what are the anabolic factors of cartilage matrix turnover and what do they do?
TGF beta and IGF 1
stimulate proteoglycan synthesis and counteract effects of IL1
what are the markers of cartilage degredation?
serum and synovial keratin sulphate
- increase = cartilage breakdown
type 2 collagen in synovial fluid
- increase = cartilage breakdown
give 4 examples of problems that can arise in a joint?
osteoarthritis - cartilage and synovial composition deteriorate
rheumatoid arthritis - synovial cell proliferation and inflammation cause rheumatoid arthritis
what causes rheumatoid arthritis?
synovial cell proliferation and inflammation cause rheumatoid arthritis
what causes gouty arthritis?
deposition of salt crystals (e.g uric acid)
what causes tendonitis?
injury and inflammation to periarticular structures causing soft tissue rheumatism - injury to the tendon
3 changes in subchondral bone in osteoarthritis?
cyst formation
osteophyte formation
sclerosis
what are the 3 types of joint?
synovial
fibrous
cartilaginous
describe fibrous joints
syanthrosis unites bone (e.g skull sutures) doesn't allow any movement
describe cartilaginous joints
AKA amphiarthrosis
bones united by cartilage
allows limited movement
e.g - IV discs, pubic symphysis
what are synovial joints?
diarthrosis
bones separated by a cavity containing synovial fluid and united by a fibrous capsule as well as extra-articular structures
what lines the inner aspect of fibrous capsule of synovial joints?
synovial membrane
- vascular connective tissue with capillary networks and lymphatics
what is the function of the synovial membrane?
contains synovial cells which produce synovial fluid
what covers the articular surfaces?
hyaline cartilage
what are the 2 types of synovial joint?
simple (one pair of articular surfaces)
compound (more than one pair of articular surfaces - eg. elbow)
