Synovial Fluid Flashcards
What is the synovium?
Synovial membrane
What makes up the epithelium of the synovium?
Synoviocytes
How thick is the epithelium of the synovium?
1-3 cells thick
What are the 2 types of synoviocytes and what is the difference between them?
Type A bone marrow derived macrophage
Type B fibroblast-like connective tissue cell
What do the synoviocytes sit on?
Directly on loose CT as there is no basement membrane so synovial fluid freely moves into cavity and there is continual production
What is the subintima?
Loose CT
Dense network of fenestrated capillaries allowing filtrated blood to enter cavity
What does the synovial fluid contain?
Hyaluronic acid
Ultrafiltrate of blood
How much synovial fluid is in the cavities?
1-2ml approx.
Why are type A synoviocytes needed?
No basement membrane so bacteria can easily enter and don’t want any in synovial fluid
What do Type B synoviocytes do?
fibroblasts - make proteoglycans to be added to synovial fluid, and hyaluronic acid
What colour should synovial fluid be?
Clear, transparent, no cells inside
What is a haemartherosis?
Dense network of fenestrated capillaries are torn/damaged so bleed into the cavity, no basement membrane so not impeded, makes synovial fluid red
What is the general composition of blood plasma?
Hyaluronate - gives viscosity
Lubricin - glycoprotein
rest same as plasma (WBCs, glucose, albumin & globulin proteins, ions lactate, 7.38 pH)
How far are the articulating surfaces from each other?
50um with synovial fluid between
Where does water in the articular cartilage come from
articulating cartilage is made up of 80% water
comes from the synovial fluid
What is the articular cartilage reliant on?
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
At rest what does the hyaluronic acid do?
At joints which aren’t being used tangles together to form a gel
What does hyaluronic acid do during movement?
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)
What is thixotropy?
tomato ketchup
gels at rest
movement ungels
What are Newtonian characteristics?
No gel/viscosity change during resting vs. movement
What is hyaluronic acid an example of?
GAG
How does hyaluronate change?
With age, get older get shorter fragments and chains
How does the synovial fluid respond to different movements?
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
What is lubricin?
Soluble glycoprotein
protein gives negative charge
sugar allows it to be soluble
What is lubricin produced by?
produced by chondrocytes and synoviocytes
What does lubricin form?
forms protective barrier for outside articular cartilage
How does the protein in lubricin allow it to do?
2 negative charges repel so articular cartilages are pushed apart preventing damage to it
What is the 2 directional movement between the synovial fluid and the articular cartilage?
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
What is articulating cartilage made up of?
Hyaline cartilage Collagen type II (Fibres) Polysaccharide glycosaminoglycans (GAGs) usually covalently linked to protein forming proteoglycans. chondrotin sulphate keratan sulphate
What forms the hydrating gel-like substance in articulating cartilage?
GAGs and proteoglycans
What does the structure of articulating cartilage allow?
Allows diffusion of nutrients, metabolites and hormones between blood and cartilage cells.
What is the role of articulating cartilage?
Shock absorber to underlying bone
Low friction movement
Attachment to subchondral bone
Which areas are less compressible in the articular cartilage?
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
What are the properties of the 3 layers of the articulating cartilage?
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
What are in the pockets formed by the collagen?
water, GAGs and Proteoglycans
aggrecan is major proteoglycan
core protein with GAG side chains
What forms these pockets
collagen type 2
