Joints and Synovial Fluid and Cartilage

Question 1

What are the types of joints? Brief description of each

Answer 1

Fibrous - 2 bones held together by collagen fibres

Cartilaginous - 2 bones held together by cartilage (less regularly arranged, lower tensile strength)

Synovial

Question 2

What are some examples of fibrous joints?

Answer 2

• Periodontal ligaments (teeth)
• Cranial sutures
• In arms and legs: interosseous membranes

Question 3

What are the 2 types of cartilaginous joints? Brief description of each

Answer 3

1. Synchondrosis / Primary: composed of only hyaline cartilage (in growing long bones)
2. Symphysis: composed of both hyaline and fibrocartilage (eg. intervertebral disc: layer of hyaline cartilage over vertebrae, fibrous cart. in middle)

Question 4

What are the general features of a synovial joint?

Answer 4

• Fibrous capsule encapsulating the joint
• Lines the inner surface of synovial capsule
• Articular cartilage covers the bone
• Synovial fluid fills the capsule

Question 5

What are some less common features of synovial joints?

Answer 5

• Articular discs (fibrocartilage)
• Ligaments
• Bursae (fluid filled capsules)

Question 6

What are the types of synovial joints?

Answer 6

• Plane
• Hinge
• Ball and socket
• Saddle
• Pivot
• Condylar

Question 7

What are some important factors in determining the stability of a joint?

Answer 7

• Shape of the articulating surfaces
• Capsule and ligaments
• Muscles

Question 8

What type of cartilage is articular cartilage?

Answer 8

Hyaline cartilage

Question 9

Is fibrocartilage or hyaline cartilage stonger?

Answer 9

fibrocartilage

Question 10

What are the two layers of articular cartilage? How do the chondrocytes differ in each of the layers?

Answer 10

1. Superficial / tangential layer: flat chondrocytes that produce collagen and glycoproteins (lubricin)
2. Transitional layer: round chondrocytes that produce proteoglycans such as aggrecan

Question 11

How does the orientation of collagen fibres change from the tangential layer deeper towards the bone?

Answer 11

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

Question 12

Why are the collagen fibres orientated as they are in the articular cartilage?

Answer 12

Different forces predominate at different points in the cartilage

• At articular surface: shearing forces pulling cartilage apart
• At bone: compression forces

Question 13

What component of articular cartilage is particularly good at binding water? What percentage of articular cartilage is water? Why is this important?

Answer 13

• Aggrecan
• AC is >75% water (when healthy)
• Because water is incompressible, takes force off the tissue

Question 14

What are glycoproteins? Example of one involved in cartilage?

Answer 14

Proteins with oligosaccharides attached to them

• Lubricin

Question 15

What are proteoglycans? Example of one involved in cartilage?

Answer 15

proteins that are heavily glycosylated (protein core with one or more GAGs attached)

• Aggrecan

Question 16

What are GAGs? Characteristics making them important in cartilage?

Answer 16

Glycosaminoglycans - long unbranched polysaccharides

• Highly polar and thus attract water

Question 17

What are three characteristics of cartilage that make it quite different from other body tissues?

Answer 17

• Avascular
• Aneural
• Alymphatic

Question 18

What type of tissue makes up the synovial membrane? What is the function of this tissue?

Answer 18

• 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

Question 19

What are the two types of synoviocytes? Characteristics of each?

Answer 19

Type A:

• Macrophage like, remove debris
• Contribute to synovial fluid production

Type B:

• Fibroblast like
• Main producers of synovial fluid

Question 20

Since cartilage is avascular and alymphatic for the most part, how does it receive nutrients and remove waste/

Answer 20

Via synovial fluid

Question 21

What are some components and characteristics of synovial fluid?

Answer 21

• Hyaluronic acid, lubricin & fluid component from blood plasma
• Present in small volumes
• Rapid turnover (~2 hours)

Question 22

Functions of synovial fluid?

Answer 22

• Lubrication
• Removal of waste
• Supply nutrients to cartilage

Question 23

What are the three types of lubrication via fluid in synovial joints? Brief description of each?

Answer 23

• 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

Question 24

What are bursae? Where do they tend to be located?

Answer 24

• Fluid filled sacs composed of synovial membrane (pillows)

- Function to reduce friction, so present at joints where high friction may be likely

Question 25

What are some changes that occur within synovial joints with age?

Answer 25

• Viscosity of synovial fluid increases (slower movement and reduced lubrication)
• Water content of cartilage decreases (reduced shock absorption)