Articular cartilage - structure and function Flashcards
What is articular cartilage composed of?
Collagen fibres
Proteoglycans
Chondrocytes
What does the synovium consist of?
1-3 layers of macrophages and fibroblast cells
It produces synovial fluid
What is the function of synovial fluid?
Lubricates tissue surfaces (i.e. joint) and supplies nutrients to articular cartilage
What is the joint capsule composed of and describe it’s structure?
Composed of collagenous fibres ad it is continous with the periosteum covering bone
Describe the characteristics of articular cartilage
Avascular
Aneural
Hypocellular
No lymphatics
No basement membrane
What are the cells of cartilage and where is their site?
Chondrocytes (specialised fibroblasts) secrete the cartilage which they become embedded in
Sit in lacunae (cavity)
What prevents nutrients entering from the bone?
Tide mark
=> cartilage must get its supply from synovium
Describe the structure of articular cartilage
Zones:
- superficial
- midzone
- deep zone
- tidemark
- calcified zone
- bone
What are beninghoff arcades?
Fibres arranged in arch formation, with chondrocytes sitting in lacunae between fibres
What collagen types makes up cartilage?
Type II (94%)
Type XI (3%)
Type IX (2%)
Type VI (1%)
What is the function of type II collagen?
Make up microfibrils (3 molecules in a triple helix) which prove tensile strength
What is the function of type XI collagen?
Glue microfibrils together into fibrils (5 microfibrils)
What is the function of type IX collagen?
Resist shear forces
By anchoring fibrils to other matrix constituents
What is the function of type VI collagen?
Forms meshwork around chondrocytes in lacunae
What is the major proteoglycan of articular cartilage?
Aggrecan
What is the structure of aggrecan?
Core protein
- anchors aggrecan molecule to hyaluronic acid at one end
- long chain binds to Glycosaminoglycans along its length
Glycosaminoglycans
- binds water due to high negative charge density
What are the molecues that make up glycosaminoglycans?
Chondroitin sulphate (65%)
Keratin sulphate (35%)
How are aggrecan formations formed?
Multiple aggrecans can bind to one hyaluronic acid chain
What is the function of aggrecan?
Absorbs compressive force through binding water
How is water pulled back into aggrecan after released by force?
Electronegative glycosaminoglycans pull water back in
What is the function of the smaller proteoglycans?
Multiple non-aggregating proteoglycans that control matrix growth
Give examples of smaller proteoglycans
Biglycan
Decorin
Fibromodulin
