joints Flashcards
ttypes of joins
synovial
fibrous
cartilaginous
accessory structures- ligaments and tendons
synovial joint structure + components
joint capsule- fibrous tissue
synovial membrane-lines joint capsule,
- intima- inner celluar layer of macrophages and fibroblasts
- deeper layer- loose connective tissue + capillaries, no basement membrane
synovial fluid- small volume, protein content ~30% of plasma, hyaluronate (viscosity) and glycoproteins (lubrication) secreted by cells in synovial initima
fibroblasts respond to inflammation in joint
articular cartilage constituents
chondrocytes (<10%)- matrix producing cells + secrete proteolytic enzymes to allow slow cartilage turonver
collagen- (15-22%) - predominantly type 2, forms network providing tensile strength
proteoglycans (4-7%)- hyaluronan backbone- chondroitin suplhae side chains + keratin sulphate side chains, bind water forming jelly like material allowing shock absorption
water = 60-85%
articular cartilage structure
superficial layer-thin collagen fibres parallel to surface
middle layer- randomly orientates collagen fibres and chondrocytes in matrix
deep layer- thicker collagen fibres + chondrocytes in colums
tidemark- border between calcified and uncalcified cartilage
calcified cartilage- fibres interlaced with bone, some capillary infiltration
top layers of cartilage dont have capillaries
chondrocyte- ageing
mitochondrial dysfunction
changes with ageing
-increased ROS production
- impaired responsiveness to growth factors eg IGF1
- reduced gene expression and matrix protein synthesis
chrondrocyte- ageing
cellular senescence
senescence associated secretory phenotype
- increased production of enzymes that break down matrix
- matrix metalloproteinases (MMP) break down type 2 collagen, aggrecanases breakdwon protoeglycans- response to injury- good normally but detrimental in ageing
fibrous tissue- ageing
includes collagen, elsatin and reticular
age changes include glycation
- non enzyme reactions of sugars with lysine and arginine residues–> advanced glycation end products
- crsoss linking of collagen- increases strength and rigidity but reduced elasticity and increased risk of damage
proteoglycans + ageing
shorter hylauronic acid backbone
molecules become less branched
lower KS and CS content
less ability to bind water
affects protein composition of collagen and water content
synovial
artic cartilage + ageing
may become thinner/altered protein content
- occurs as damage occurs to cartilage
decreased strength and elasticity- increased forces acting on cartilage, increased risk of damage
less anabolic response to damage- less responsiveness to IGF1 so cant repair damage as efficiently
synovial fluid canreduce in quantity/protein content
fibrous joints + ageing
eg intervertabral discs
reduction in ground substance proteins- reduction in height
increased stiffness
increased risk of injury eg herniated disc
cartilaginous joints + ageing
continued calcification may occur in some cartilage eg costal cartilages- reduced elasticity
ligaments and tendons
ligament- bone to bone
tendon- muscle to bone
consituents of L+T
cellular matrix- 20%- fibroblasts
extracellular matrix- 80% incl:
water- 60-80%
solids- 20-40%- includes collagen 70-80% (more in tendons)
- type 1-90% in ligaments and 95-99% in tendons
- type 3 remainder
ground substance- 20-30% includes proteoglycans and glycoproteins
metabolism
limited blood supply
slow collagen turnover (half life 300-500 days)
metabolic activity greater in ligaments than tendons
activity increased in growth/injury
L+T and ageing
elasticity declines with age
reduced ROM and increased risk of damage
