arthritis and ATH Flashcards
osteoarthritis
the most common type of joint disease. a degenerative joint disease - a breakdown of the cartilage matrix
structure of the synovial joint
-synovial membrane
-articular cartilage
-synovial fluid
-joint capsulesy
synovial membrane
a special type of biological membrane without an epithelium. Inner lining is provided by synovial lining macrophages and synovial fibroblasts (synoviocytes)
synoviocytes
synovial fibroblasts that produce synovial fluid
synovial fluid contains
- inflammatory and immune cells
- is high in glucose (3.5-5.5mm/l) to nourish and feed the avascular chondrocytes.
- hyaluronic acid makes the fluid viscous and slippery
synovial fluid functions
- provides nutrients for cartilage
- acts as a lubricant
- lessens the impact of mechanical forces exerted on the joint
Articular cartilage
- a hyaline cartilage
- contains chondrocytes that sit in lacunae
- avascular, and thus has no capacity to regenerate after damage
hyaline cartilage
allows a virtually frictionless movement of synovial joints as it is resistant to both tension and compression due to type II collagen and Proteoglycans respectively.
it has a relaxation and compression function promoting the movement of water in and out of the cartilage, allowing the survival of chondrocytes
collagen
collagens are extremely strong and resistant to normal shearing and tearing forces.
- it is the most abundant protein in the human body
proteoglycans
attached to long filaments of hyaluronic acid, attached by a link protein.
aggrecan
building structure of hyaline cartilage ground substance.
- Proteoglycans-link protein-hyaluronic acid
hyaline substance ground substance structure
the collagen fibres of type II collagen binds electrostatically to the sulphated side chains of the aggrecan.
- this forms a strong elastic material
primary (idiopathic) arthritis
no apparent initiating cause and mostly oligoarticular (only one or a few joints are affected)
- 95% of all cases
secondary osteoarthritis
occurs in younger individuals with some predisposing condition
steps in developing osteoarthritis
- chondrocyte injury (driven by genetic and biochemical factors) (early osteoarthritis)
- chondrocytes proliferate and secrete inflammatory mediators, collagens, and proteases -> cartilaginous matrix remodelling
- chondrocytes get hypertrophic and form clusters (cloning)
- matrix metalloproteinases degrade type II collagen
- chondrocytes continuously synthesize and secrete proteoglycans, but degradation exceeds synthesis, and the composition of proteoglycans also changes
- the water content of the matrix increases = concentration of proteoglycans decreases
- The physiologically horizontally arranged collagen fibres in the superficial zone are cleaved, producing fissures and clefts at the articular surface, making it soft and granular.
- repetitive injury and chronic inflammation lead to chondrocyte drop out, secondary inflammatory changes in the synovium and subchondral bone
step 1 osteoarthritis
chondrocyte injury (driven by genetic and biochemical factors)