Joints and Synovial Fluid

Question 1

What are the 3 types of joints?

Answer 1

Fibrous, cartilaginous, synovial

Question 2

Give three types of fibrous joints

Answer 2

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

Question 3

What are the two types of cartilaginous joints? What are they made up from? Give examples of each

Answer 3

Primary/synchondrosis (ONLY HYALINE) - epiphyseal growth plates
Secondary/symphysis (HYALINE and FIBROCARTILAGE), these usually occur in the midline, e.g. pubic symphysis

Question 4

What are the 6 types of synovial joints and give examples of each?

Answer 4

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

Question 5

What are the constituents of a synovial joint?

Answer 5

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.

Question 6

Upon what 3 things does joint stability depend on?

Answer 6

Shape of the articular cartilage
Supporting ligaments and capsule
Muscles

Question 7

What are the layers of articular cartilage?

Answer 7

Superficial/tangenital layer: consists of flattened chondrocytes that produce collagen and glycoproteins
Intermediate/transitional layer: consists of round chondrocytes that produce proteoglycans
Deep layer

Question 8

How does the collagen fibre orientation change as you go from the superficial layer of articular cartilage to the deep layer?

Answer 8

Collagen fibres initially are horizontally arranged and they become oblique in the transitional layer and finally, vertical in the deep layer

Question 9

What is the major constituent of articular cartilage?

Answer 9

> 75% water - this is good because water is incompressible

Question 10

What are glycoproteins? Give an example

Answer 10

Proteins to which oligosaccharides are attached
(protein > carb)
E.g. lubricin

Question 11

What is lubricin?

Answer 11

A glycoprotein that is secreted into synovial joints and lubricates them

Question 12

What are proteoglycans? Give an example

Answer 12

Proteins that are heavily glycosylated (carb > protein) (i.e. a protein to which more than one GAG attaches)
Aggrecan for e.g.

Question 13

What is aggrecan?

Answer 13

Proteoglycan that forms a hydrated gel structure in the joint and provides load bearing properties

Question 14

What are glycosaminoglycans? Give an example

Answer 14

Long unbranched polysaccharides which are very polar and therefore attract water
E.g. hyaluronic acid

Question 15

What is hyaluronic acid?

Answer 15

GAG that has elastic shock absorbance properties

Question 16

The more force a joint must take, the thicker/thiner the articular cartilage is.

Answer 16

THICKER

Question 17

What are 3 properties of cartilage?

Answer 17

Avascular, aneural, alymphatic

Question 18

What is the average thickness of articular cartilage?

Answer 18

2-3mm

Question 19

How are nutrients transported to articular cartilage and how are wastes removed?

Answer 19

Via synovial fluid

Question 20

Does the synovium directly have a capillary network?

Answer 20

Has a rich capillary network

No epithelial lining so there is direct exchange of gases and nutrients between blood and synovial fluid

Question 21

What cells produce synovial fluid?

Answer 21

Synoviocytes

Question 22

What are the two types of synoviocytes and how do they differ?

Answer 22

Type A - look like macrophages, remove debris and produce synovial fluid

Type B - look like fibroblasts, MAIN producer of synovial fluid

Question 23

What is synovial fluid?

Answer 23

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)

Question 24

What are the functions of synovial fluid?

Answer 24

Nutrition of cartilage (articular, menisci/discs)
Removal of waste products
Lubrication –> less friction –> less wear and tear

Question 25

What are the three ways in which joints are lubricated?

Answer 25

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)

Question 26

Define friction

Answer 26

Force that resists surfaces from sliding against each other

Question 27

What is the co-efficient of friction?

Answer 27

Used to measure friction (higher coefficients are given to rougher surfaces)

Question 28

What are bursae?

Answer 28

Fluid filled sacs lined w. synovial membrane

Question 29

What is the function of bursae?

Answer 29

Reduce friction

Question 30

What is bursitis?

Answer 30

Inflammation of bursa

Question 31

What happens to our joints as we age?

Answer 31

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