Synovial Fluid

Question 1

Describe the composition of the synovial membrane

Answer 1

Membrane 1-3 cells thick and has two types of cell:
Type A cells - bone marrow derived macrophages (immune surveillance)
Type B cells - fibroblast-like connective tissue cells which make proteoglycans to be added to fluid
There is also no basement membrane

Question 2

Describe the composition of the subintima of the synovial membrane

Answer 2

Contains a dense network of fenestrated capillaries (allows large amount of fluid flow)

Question 3

How does the synovial fluid work to reduce friction between articulating bones?

Answer 3

Synovial fluid also seeps into articular cartilage to create slippery, weight-bearing film to reduce friction between cartilages, distribute force across surface, and helps nourish articular cartilage (which is avascular and aneural)

Question 4

What type of non-ordinary flow does synovial fluid demonstrate?

Answer 4

Non-newtonian

Question 5

What happens to the water in synovial fluid when it is compressed and then relaxed?

Answer 5

Water is forced out of articular cartilages (weeping lubrication) then this seeps back into cartilage micro-cavities and irregularities in articular cartilage on relaxation.

Question 6

Describe the thixotropic flow of synovial fluid

Answer 6

At rest the synovial fluid ‘gels’ whereas with movement it becomes less viscous

Question 7

Describe the response of synovial fluid to low frequency exercise

Answer 7

Molecules of hyaluronic acid align in the direction of movement so energy is dissipated as the viscous fluid flows.

Question 8

Describe the response of synovial fluid to high frequency exercise

Answer 8

Molecules of hyaluronic acid form an entangled molecular network which resists deformation and acts as shock absorption, storing the energy as elasticity.

Question 9

What is ‘lubricin’?

Answer 9

Water soluble glycoprotein which contains equal proportions of protein and oligosaccharides and is produced by synoviocytes and chondrocytes.

Question 10

Describe the role of lubricin in synovial fluid

Answer 10

Forms the thin superficial barrier that repels joint surfaces and prevents contact between articular surfaces

Question 11

Describe the composition of the articular cartilage at the ends of bone

Answer 11

Hyaline cartilage containing type II collagen fibres, GAGs and proteoglycans (these two work to form the hydrated gel-like substance which allows diffusion of nutrients, metabolites and hormones between blood and cartilage cells)

Question 12

Describe the extracellular matrix of articular cartilage

Answer 12

Up to 80% water, had mainly type II collagen fibres which form a network that give the overall framework/shape of the cartilage as well as making water-filled pockets. Avascular and aneural and requires diffusion of nutrients into matrix to survive.

Question 13

What are ‘proteoglycans’?

Answer 13

Special class of glycoprotein that are heavily glycosylated. Consist of core protein with one or more covalently attached glycosaminoglycan chains

Question 14

What is the main proteoglycan present in articular cartilage?

Answer 14

Aggrecan

Question 15

Briefly outline the 5 histological zones of the articular cartilage

Answer 15

1) Superficial zone - flat cells with parallel collagen
2) Middle zone - more rounded, fat cells with random, oblique and thick collagen fibres (haphazard)
3) Deep zone - spherical cells in columns, vertically arranged collagen fibres, (then tidemark)
4 Calcified zone - has smaller cells
5) Bone osteoblasts

Question 16

How do GAGs contribute to the lubricating properties of the synovial joint?

Answer 16

negative charge draws water into the cell, which creates a gel-like substance that works to reduce friction

Question 17

How is synovial fluid produced?

Answer 17

By the synovial membrane as it is an ultrafiltrate of blood with added hyaluronic acid