Joints and Synovial Fluid

Question 1

What are the three main types of joint?

Answer 1

Fibrous
Cartilaginous
Synovial

Question 2

Describe the mobility of the three main types of joint?

Answer 2

Fibrous- very immobile
Cartilaginous- slightly mobile but still not very mobile
Synovial- mobile

Question 3

What makes up the joints in fibrous joints?

Answer 3

Fibrous joints- collagen fibres and fibrous connective tissue

Question 4

What makes up the joints in cartilaginous joints?

Answer 4

Cartilage and some collagen fibres

Question 5

Where in the body are fibrous joints found?

Answer 5

Periodontal ligament
Cranial sutures
Interosseus membranes

Question 6

What are the two types of cartilaginous joints?

Answer 6

Primary cartilaginous or synchondrosis

Secondary cartilaginous or symphysis

Question 7

What makes up primary and secondary cartilaginous joints?

Answer 7

Primary- Hyaline cartilage only

Secondary- Hyaline cartilage and fibrocartilage

Question 8

Where are primary and secondary cartilaginous joints found?

Answer 8

Primary- growth plate

Secondary- intervertebral discs

Question 9

What are the common and rarer features of a synovial joint?

Answer 9

Common features:
-Synovial cavity (fluid filled)
-Articular cartilage
-Fibrous capsule
-Synovial membrane 
Rarer features:
-Articular discs
-Bursa
-Ligaments

Question 10

What are the different kinds of synovial joints?

Answer 10

Plane
Hinge 
Pivot
Condylar 
Ellipsoid
Ball and socket

Question 11

What are the factors contributing to joint stability?

Answer 11

Shape of articulating surfaces
Capsules and ligaments
Muscles

Question 12

What are the histological differences between hyaline cartilage and fibrocartilage?

Answer 12

Fibres are present in hyaline cartilage but not as densely packed as in fibrocartilage so the hyaline fibres do not show on histology.

Question 13

What are the characteristics of the superficial/tangential layer of articular cartilage?

Answer 13

Flattened chondrocytes that produce collagen and glycoproteins

Question 14

What are the characteristics of the transitional layer of articular cartilage?

Answer 14

Round chondrocytes that produce proteoglycans such as aggrecan

Question 15

Describe the orientation of collagen fibres in articular cartilage?

Answer 15

They lie parallel to the surface in the superficial layer, become more oblique in the transitional layer and lie perpendicular to the surface in the deep layers

Question 16

What is the water content of articular cartilage and how does it change with age?

Answer 16

~75%, decreasing with age

Question 17

What are glycoproteins?

Answer 17

Proteins to which oligosaccharide chains are attached

Question 18

What are proteoglycans?

Answer 18

Proteins that are heavily glycosylated

Question 19

What are glycosaminoglycans?

Answer 19

Long, unbranched polysaccharides that are highly polar and attract water

Question 20

What influences the thickness of articular cartilage?

Answer 20

Forces acting on the cartilage

Question 21

How do nutrients reach the cartilage within joints and why is this necessary?

Answer 21

Nutrients reach the joint through the synovial fluid. This is necessary because the cartilage is avascular, alymphatic and aneural, except from at the peripheries where there are some vessels

Question 22

Describe the characteristics of the synovium

Answer 22

Synoviocytes producing the fluid
Rich capillary network, through which exchange of nutrients between blood and synovial fluid
No epithelial lining so synovial fluid can enter joint easily

Question 23

What are the characteristics of the two types of synoviocytes?

Answer 23

Type A- look like macrophages, removes debris, contributes to synovial fluid production
Type B- fibroblast like, main producer of synovial fluid

Question 24

What are the contents of synovial fluid?

Answer 24

Viscous fluid
Hyaluronic acid
Lubricin
Fluid component (taken from blood plasma)

Question 25

What are the functions of synovial fluid?

Answer 25

Nutrition of cartilage
Removal of waste products
Lubrication to reduce wear

Question 26

What are the different kinds of lubrication?

Answer 26

Boundary- glycoproteins bind to receptors on articular surface to form a thin film
Hydrodynamic- surfaces kept apart by liquid pressure
Weeping- fluid that is present in the cartilage is squeezed out into the synovial cavity to increase fluid volume

Question 27

What are the characteristics of bursae?

Answer 27

Synovial membrane
Fluid-filled
Reduces friction

Question 28

What affects do ageing have on joints?

Answer 28

Viscosity of synovial fluid increases- slower joint movements and reduced lubrication
Water content of cartilage decreases- reduced shock absorption
Both cause less protection of articular surfaces and an increased risk of damage