Joints and Synovial Fluid Flashcards
What are the 3 types of joints?
Fibrous, cartilaginous, synovial
Give three types of fibrous joints
Suture (cranial sutures)
Syndesmosis (two bones connected by fibrous tissue), e.g. interosseous membrane/radioulnar syndesmosis
Gomphosis - between the roots of the teeth and mandible/maxilla
What are the two types of cartilaginous joints? What are they made up from? Give examples of each
Primary/synchondrosis (ONLY HYALINE) - epiphyseal growth plates
Secondary/symphysis (HYALINE and FIBROCARTILAGE), these usually occur in the midline, e.g. pubic symphysis
What are the 6 types of synovial joints and give examples of each?
Pivot - alanto-axial joint Saddle - first carpometacarpal joint Condyloid - metacarpal phalangeal joint Hinge - elbow or knee Ball and socket - hip or shoulder Plane - acromioclavicular joint
What are the constituents of a synovial joint?
Synovial fluid in the synovial cavity
Articular cartilage on the articulating surfaces of the bones
Fibrous capsule lined internally by the synovial membrane
May also have: bursae, ligaments, articular discs etc.
Upon what 3 things does joint stability depend on?
Shape of the articular cartilage
Supporting ligaments and capsule
Muscles
What are the layers of articular cartilage?
Superficial/tangenital layer: consists of flattened chondrocytes that produce collagen and glycoproteins
Intermediate/transitional layer: consists of round chondrocytes that produce proteoglycans
Deep layer
How does the collagen fibre orientation change as you go from the superficial layer of articular cartilage to the deep layer?
Collagen fibres initially are horizontally arranged and they become oblique in the transitional layer and finally, vertical in the deep layer
What is the major constituent of articular cartilage?
> 75% water - this is good because water is incompressible
What are glycoproteins? Give an example
Proteins to which oligosaccharides are attached
(protein > carb)
E.g. lubricin
What is lubricin?
A glycoprotein that is secreted into synovial joints and lubricates them
What are proteoglycans? Give an example
Proteins that are heavily glycosylated (carb > protein) (i.e. a protein to which more than one GAG attaches)
Aggrecan for e.g.
What is aggrecan?
Proteoglycan that forms a hydrated gel structure in the joint and provides load bearing properties
What are glycosaminoglycans? Give an example
Long unbranched polysaccharides which are very polar and therefore attract water
E.g. hyaluronic acid
What is hyaluronic acid?
GAG that has elastic shock absorbance properties
The more force a joint must take, the thicker/thiner the articular cartilage is.
THICKER
What are 3 properties of cartilage?
Avascular, aneural, alymphatic
What is the average thickness of articular cartilage?
2-3mm
How are nutrients transported to articular cartilage and how are wastes removed?
Via synovial fluid
Does the synovium directly have a capillary network?
Has a rich capillary network
No epithelial lining so there is direct exchange of gases and nutrients between blood and synovial fluid
What cells produce synovial fluid?
Synoviocytes
What are the two types of synoviocytes and how do they differ?
Type A - look like macrophages, remove debris and produce synovial fluid
Type B - look like fibroblasts, MAIN producer of synovial fluid
What is synovial fluid?
Viscous fluid that consists of hyaluronic acid, lubricin and a fluid component (from blood plasma)
Present in v small volumes in joints and has a rapid turn-over (about 2h)
What are the functions of synovial fluid?
Nutrition of cartilage (articular, menisci/discs)
Removal of waste products
Lubrication –> less friction –> less wear and tear
What are the three ways in which joints are lubricated?
Boundary - glycoproteins (e.g. lubricin) bind to receptors on articular surfaces and form a thin film
Hydrodynamic (like aquaplaning) - surfaces kept apart by liquid pressure, viscosity changes with load and velocity of movement
Weeping - fluid in cartilage squeezed out into synovial cavity to increase fluid volume (during movement fluid is mechanically squeezed out)
Define friction
Force that resists surfaces from sliding against each other
What is the co-efficient of friction?
Used to measure friction (higher coefficients are given to rougher surfaces)
What are bursae?
Fluid filled sacs lined w. synovial membrane
What is the function of bursae?
Reduce friction
What is bursitis?
Inflammation of bursa
What happens to our joints as we age?
Viscosity of synovial fluid increases –> slower joint movements and less lubrication
Water content of cartilage decreases –> less shock absorption
–> less protection of articular surfaces –> risk of damage
