Joints and Synovial Fluid and Cartilage Flashcards
What are the types of joints? Brief description of each
Fibrous - 2 bones held together by collagen fibres
Cartilaginous - 2 bones held together by cartilage (less regularly arranged, lower tensile strength)
Synovial
What are some examples of fibrous joints?
- Periodontal ligaments (teeth)
- Cranial sutures
- In arms and legs: interosseous membranes
What are the 2 types of cartilaginous joints? Brief description of each
- Synchondrosis / Primary: composed of only hyaline cartilage (in growing long bones)
- Symphysis: composed of both hyaline and fibrocartilage (eg. intervertebral disc: layer of hyaline cartilage over vertebrae, fibrous cart. in middle)
What are the general features of a synovial joint?
- Fibrous capsule encapsulating the joint
- Lines the inner surface of synovial capsule
- Articular cartilage covers the bone
- Synovial fluid fills the capsule
What are some less common features of synovial joints?
- Articular discs (fibrocartilage)
- Ligaments
- Bursae (fluid filled capsules)
What are the types of synovial joints?
- Plane
- Hinge
- Ball and socket
- Saddle
- Pivot
- Condylar
What are some important factors in determining the stability of a joint?
- Shape of the articulating surfaces
- Capsule and ligaments
- Muscles
What type of cartilage is articular cartilage?
Hyaline cartilage
Is fibrocartilage or hyaline cartilage stonger?
fibrocartilage
What are the two layers of articular cartilage? How do the chondrocytes differ in each of the layers?
- Superficial / tangential layer: flat chondrocytes that produce collagen and glycoproteins (lubricin)
- Transitional layer: round chondrocytes that produce proteoglycans such as aggrecan
How does the orientation of collagen fibres change from the tangential layer deeper towards the bone?
At articular surface: collagen fibres are parallel to articular surface (flat)
Moving deeper to transitional layer fibres become more oblique
Right next to bone surface: fibres are perpendicular to articular surface
Why are the collagen fibres orientated as they are in the articular cartilage?
Different forces predominate at different points in the cartilage
- At articular surface: shearing forces pulling cartilage apart
- At bone: compression forces
What component of articular cartilage is particularly good at binding water? What percentage of articular cartilage is water? Why is this important?
- Aggrecan
- AC is >75% water (when healthy)
- Because water is incompressible, takes force off the tissue
What are glycoproteins? Example of one involved in cartilage?
Proteins with oligosaccharides attached to them
- Lubricin
What are proteoglycans? Example of one involved in cartilage?
proteins that are heavily glycosylated (protein core with one or more GAGs attached)
- Aggrecan
What are GAGs? Characteristics making them important in cartilage?
Glycosaminoglycans - long unbranched polysaccharides
- Highly polar and thus attract water
What are three characteristics of cartilage that make it quite different from other body tissues?
- Avascular
- Aneural
- Alymphatic
What type of tissue makes up the synovial membrane? What is the function of this tissue?
- Synovium
- Produces synovial fluid
- Since it has no epithelial lining and a rich capillary supply, there is direct exchange of oxygen, carbon dioxide & metabolites between blood and synovial fluid
What are the two types of synoviocytes? Characteristics of each?
Type A:
- Macrophage like, remove debris
- Contribute to synovial fluid production
Type B:
- Fibroblast like
- Main producers of synovial fluid
Since cartilage is avascular and alymphatic for the most part, how does it receive nutrients and remove waste/
Via synovial fluid
What are some components and characteristics of synovial fluid?
- Hyaluronic acid, lubricin & fluid component from blood plasma
- Present in small volumes
- Rapid turnover (~2 hours)
Functions of synovial fluid?
- Lubrication
- Removal of waste
- Supply nutrients to cartilage
What are the three types of lubrication via fluid in synovial joints? Brief description of each?
- Boundary: glycoproteins such as lubricin bind receptors on articular surfaces to form a thin film
- Hydrodynamic (like aquaplaning): contact is lost between two bones and joint fluid takes on force
- Weeping: under pressure fluid present in joint cartilage is squeezed out to increase lubrication volume
What are bursae? Where do they tend to be located?
- Fluid filled sacs composed of synovial membrane (pillows)
- Function to reduce friction, so present at joints where high friction may be likely
What are some changes that occur within synovial joints with age?
- Viscosity of synovial fluid increases (slower movement and reduced lubrication)
- Water content of cartilage decreases (reduced shock absorption)
