Synovial fluid Flashcards
the articular cartillage is avascular, so what supplies it with nutrients
the synovial fluid bathes the articular cartillage and supplies it w nutrients
n.b.articular cartilage is also aneural (no nerve supply)
what are the 2 types of synoviocytes + what is their role in the synovial fluid
- Type A - (rarer) bone marrow derived macrophage for immune surveillance (CD68+ macrophages)
- Type B - (more common) fibroblasts-like connective tissue cell for proteoglycan production - makes synovial fluid viscous (CD55+ fibroblasts)
- No _____ _____ between synoviocytes and subintima (where all blood vessels are(
- No ___ for fluid movement into joint cavity from subintima
- No basement membrane between synoviocytes and subintima (where all blood vessels are(
- No barrier for fluid movement into joint cavity from subintima
what is the subintima of the synovial membrain (synovium)
subintima=
* Loose connective tissue - type II collagen
* Contains dense network fenestrated capillaries (also found in kidneys and exocrine glands)
* Endothelia have pores
Fenestrae are 60-80 nm in diameter - lets out fluid, blood plasma, some albumin but not big macromolecules
* Capillaries surrounded by basement membrane
* Synovial fluid is an ultrafiltrate of blood with added hyaluronic acid - forms thin film over surfaces within articular capsule (1-2 ml only)
So RBC/WBCs don’t cross - some proteins like albumin just about gets through it
Not a lot of synovial fluid - in biggest joint of body, knee joint, only has 5ml - all that is needed
what is the composition of synovial fluid
synovial intimal cells, termed synoviocytes produce synovial fluid components.
Synovial fluid is produced as an ultrafiltrate of blood plasma, has a pH of about 7.38 (SAME AS BLOOD pH) is primarily composed of;
* hyaluronate (glycosaminoglycans aka GAGs, forms long chains, highly -vely charged to attracts/trap water, makes synovial fluid viscous - long chains interact with proteins, wraps around forming proteoglycotic gel)
* lubricin (coats articular cartilage + synovial membrane- has -ve charge so helps repel articular cartilages from each other)
* proteinase
* collagenases
* prostaglandins
* glucose
* some WBCs (/mm3) partly since type A cells are there being active but should be acellular
what is haemarthrosis and what will the synovial fluid look like as a result
Hemarthrosis is bleeding into joint cavity
the synovial fluid will look blood tinged, or red reflecting trauma (cld be much more)
but remember when u take sample u can get blood tinged synovial fluid cuz u could nick one of the capillaries in there
n.b. healthy synovial fluid; small volume of clear slightly yellow viscous fluid
what colour is synovial fluid of a patient with rheumatoid arthritis
Rheumatoid arthritis inflammatory - synovial fluid not as viscous so don’t protect joint as well; fluid will be yellow+ cloudy cuz of presence of WBCs in the synovial fluid
synovial fluid is thixotropic, what does this mean
thixotropic= the viscosity not constant * Viscosity decreases with movement - at rest, its more gel
=Movement detangles hyaluronic acid chains ;
With movement is less viscous
* u redilute the hyaluronic acid
* movement itself detangles the hyaluronic acid + protein
what is the function of lubricin in synovial fluid
Lubricin (aka PRG4) it is a water soluble glycoprotein
= Produced by chondrocytes and synoviocytes
function:
* Forms thin superficial barrier on both articular cartilages - repels joint surfaces, preventing contact of articular surfaces; REDUCES FRICTION and reduces stress on the most superficial layer of chondrocytes
Big head bends over so repulsive sides repels surface from other articular cartilage
what type of cartillage is articular cartilage and what type of collagen is it made up of
- Caps the ends of bones in synovial joints
- Hyaline cartilage
- Collagen type II fibres - forms scaffold for aggrecans to attach onto
Polysaccharide GAGs usually covalently linked to protein forming very large proteoglycan aggregates (aggrecan) - GAGs and proteoglycans form hydrated gel-like - -ve charges attracts water from synovial fluid
Allows diffusion of nutrients, metabolites and hormones between blood and cartilage cells
composition of articular cartilage:
* ECM is ~ 1% chondrocytes
* ECM
* ~ 70-80%
* Collagen type II 15%
* Fibril networks that give overall framework/shape of cartilage
* Makes pockets that are filled with water binding proteoglycans complexes - regulate compressibility
Proteoglycans 15% have lots of -ve charges that attract water
* Lacks blood/lymphatic vessels - survival and synthetic activity depends on diffusion of nutrients and metabolites through matrix
Chondrocytes also sits in ECM
why do we have articular cartilage?
- Elastic, resilient structure acts as shock absorber protecting the underlying bone
- Bone is only 5% water so very brittle
- Articular cartilage is 80% water
- Smooth, slippery and very low coefficient of friction
- Deeper layer merges with calcified layer (tidemark) that attaches it to subchondral bone
Superficial layers are compressible
where do u find chondrocytes and what is their role
Chondrocytes are specialised types of cells that are responsible for forming, and are only found in,** cartilage**. Cartilage is a soft, firm, flexible, and resilient connective tissue that serves as an important structural component in the body. It functions in covering and protecting the bones at the joints.
Chondrocytes are mainly responsible for the production of collagen and the extracellular matrix that will lead to the maintenance of cartilaginous tissues within joint
what are the 3 layers of chondrocytes
in articular cartilage
- Chondrocytes come in 3 layers - similar to epiphyseal growth plate
- Superficial - resting chondrocytes
- Middle - proliferating
- Deep - hypertrophy layer
- Then die and calcification can happen - make up holes for osteocytes to move in
what is the major proteoglycan/GAG in cartilage
aggrecan
- Proteoglycans special class of glycoproteins that are heavily glycosylated - lots of -ve charges
Core protein with 1/more covalently attached GAGs chains (chondroitin/keratan sulphate) - then many of these attached to long strand of hyaluronic acid
n.b. Aggrecan amount and complexity changes with age!
Young = bigger and longer complexes
Older ppl= smaller + fewer side branches
what cartilage does osteoarthritis affect
- Affects articular cartilage
- The older you are the more likely the development of osteoarthritis
*At young age the articular cartilage is smooth but if stress it a lot then it dries out, cracks and breaks causing loss of articular cartilage - bone rubs on bone causes pain (sine bone has neurovascular supply while articular don’t so don’t feel it before)
pain comes from bone rubbing on bone! more bone formation rubs on articular capsule causing pain all because all of this is innervated. In healthy ppl, our articular cartilage is in tact and since the articular cartilage has no nerve supply when we move we are not in pain
