Synovial Fluid

Question 1

What is the synovium?

Answer 1

Synovial membrane

Question 2

What makes up the epithelium of the synovium?

Answer 2

Synoviocytes

Question 3

How thick is the epithelium of the synovium?

Answer 3

1-3 cells thick

Question 4

What are the 2 types of synoviocytes and what is the difference between them?

Answer 4

Type A bone marrow derived macrophage

Type B fibroblast-like connective tissue cell

Question 5

What do the synoviocytes sit on?

Answer 5

Directly on loose CT as there is no basement membrane so synovial fluid freely moves into cavity and there is continual production

Question 6

What is the subintima?

Answer 6

Loose CT

Dense network of fenestrated capillaries allowing filtrated blood to enter cavity

Question 7

What does the synovial fluid contain?

Answer 7

Hyaluronic acid

Ultrafiltrate of blood

Question 8

How much synovial fluid is in the cavities?

Answer 8

1-2ml approx.

Question 9

Why are type A synoviocytes needed?

Answer 9

No basement membrane so bacteria can easily enter and don’t want any in synovial fluid

Question 10

What do Type B synoviocytes do?

Answer 10

fibroblasts - make proteoglycans to be added to synovial fluid, and hyaluronic acid

Question 11

What colour should synovial fluid be?

Answer 11

Clear, transparent, no cells inside

Question 12

What is a haemartherosis?

Answer 12

Dense network of fenestrated capillaries are torn/damaged so bleed into the cavity, no basement membrane so not impeded, makes synovial fluid red

Question 13

What is the general composition of blood plasma?

Answer 13

Hyaluronate - gives viscosity
Lubricin - glycoprotein
rest same as plasma (WBCs, glucose, albumin & globulin proteins, ions lactate, 7.38 pH)

Question 14

How far are the articulating surfaces from each other?

Answer 14

50um with synovial fluid between

Question 15

Where does water in the articular cartilage come from

Answer 15

articulating cartilage is made up of 80% water

comes from the synovial fluid

Question 16

What is the articular cartilage reliant on?

Answer 16

No own blood supply so:
synovial fluid soaks into articular cartilage making it a hydrating gel, takes with it glucose, oxygen, ions to nourish the cartilage and keep chondrocytes alive

Question 17

At rest what does the hyaluronic acid do?

Answer 17

At joints which aren’t being used tangles together to form a gel

Question 18

What does hyaluronic acid do during movement?

Answer 18

Stretches out, untangles, less viscous after initial point of movement
Fluid part of synovial fluid moves into articular cartilage and rehydrates it but then in movement articular cartilage i being compressed so moves back into the joint (weeping lubrication)

Question 19

What is thixotropy?

Answer 19

tomato ketchup
gels at rest
movement ungels

Question 20

What are Newtonian characteristics?

Answer 20

No gel/viscosity change during resting vs. movement

Question 21

What is hyaluronic acid an example of?

Answer 21

GAG

Question 22

How does hyaluronate change?

Answer 22

With age, get older get shorter fragments and chains

Question 23

How does the synovial fluid respond to different movements?

Answer 23

Low freq/low energy- molecules align in the direction of movement and is viscous so energy is dissipated
High freq/high energy - entangled molecular network resists deformation and acts as a shock absorber, energy is stored as elasticity

Question 24

What is lubricin?

Answer 24

Soluble glycoprotein
protein gives negative charge
sugar allows it to be soluble

Question 25

What is lubricin produced by?

Answer 25

produced by chondrocytes and synoviocytes

Question 26

What does lubricin form?

Answer 26

forms protective barrier for outside articular cartilage

Question 27

How does the protein in lubricin allow it to do?

Answer 27

2 negative charges repel so articular cartilages are pushed apart preventing damage to it

Question 28

What is the 2 directional movement between the synovial fluid and the articular cartilage?

Answer 28

oxygen, glucose, ion, hyaluronate, lubricin etc. is passed t chondrocytes as is aneural and avascular but then when there is movement it will pass back into synovial fluid

Question 29

What is articulating cartilage made up of?

Answer 29

Hyaline cartilage 
Collagen type II (Fibres)
Polysaccharide glycosaminoglycans (GAGs) usually covalently linked to protein forming proteoglycans.
chondrotin sulphate 
keratan sulphate

Question 30

What forms the hydrating gel-like substance in articulating cartilage?

Answer 30

GAGs and proteoglycans

Question 31

What does the structure of articulating cartilage allow?

Answer 31

Allows diffusion of nutrients, metabolites and hormones between blood and cartilage cells.

Question 32

What is the role of articulating cartilage?

Answer 32

Shock absorber to underlying bone
Low friction movement
Attachment to subchondral bone

Question 33

Which areas are less compressible in the articular cartilage?

Answer 33

First 2 layers are compressible
In deep layer, more columnar chondrocytes and bigger, collagen fibres are parallel to stacks so can’t be compressed as no pockets formed for GAGs

Question 34

What are the properties of the 3 layers of the articulating cartilage?

Answer 34

Superficial - flat chondrocytes, parallel collagen
Middle - fatter chondrocytes more rounded, collagen thicker and haphazard
Deep - stacked columns of chondrocytes, collagen vertical in right angle to columns

Question 35

What are in the pockets formed by the collagen?

Answer 35

water, GAGs and Proteoglycans
aggrecan is major proteoglycan
core protein with GAG side chains

Question 36

What forms these pockets

Answer 36

collagen type 2