Extracellular matrix Flashcards
What is the ECM?
Any substance produced by cells & secreted into the extracellular space within the tissues
Why is the ECM important?
> structural - provides physical support for cells & a linkage between cells/tissues
> cell mobility - forms a substrate on which cells can move & provides cues that guide direction of movement
Describe the structure of connective tissue
Scattered cells e.g. fibroblasts
Predominantly ECM
Describe the composition of ECM in connective tissues
Collagen fibres cross-linked by accessory proteins in a matrix of proteoglycans
What are proteoglycans?
Proteins bound to polysaccharides
Describe the structure of epithelial tissues
Layers of cells bound closely to form protective sheets
Minimal ECM
Describe ECM in epithelial tissues
concentrated under epithelia (basal lamina)
- provides base for cells to sit on & acts as molecular sieve & substrate for migrating cells
Describe the composition of ECM in plants
Cellulose fibres cross-linked w/ hemicellulose in matrix of highly branched polysaccharides
Describe how ECM is arranged in plants
All plant cells surrounded by ECM
= cell wall
What are cellulose fibres analogous to?
Collagen fibres
How does the ECM differ between plants & animals?
Plant ECM contain polysaccharide fibres
Animal ECM contains fibres made of protein
- collagen & elastin
What is the function of collagen?
Resists tensile force
How many different collagen genes are there in mammals?
42
How are collagen fibres formed?
- 3 single-stranded collagens cross-link
= collagen fibrils - Collagen fibrils link to form collagen fibres
In what orientation are collagen fibres organised?
In 2 orthogonal directions
= 90 degrees to each other
Give an example of a fibril forming collagen
Type II collagen
Give an example of a cross-linking collagen
Type IX collagen
- has a kink in molecule so can bind along the side of 2 fibres at diff angles
What is the function of elastin?
Provides tissues with elasticity
What is elastin composed of?
Large filaments w/ lots of random spring-like coils
What is elastin cross-linked by?
Lysine
Hydroxylysines
How is the ECM in plants similar to in animals?
Matrix consists of polysaccharides
Plants: pectin (forms hydrated gel)
Animals: glycosaminoglycans = GAGS
(e.g. hyaluronan)
What are the features of GAGS?
> highly -ve charge
hydrophilic
linked to proteoglycans
Why is a -ve charge in GAGS significant?
Carboxyl group creates -ve charge --> attracts water = swells up = cushioning affect
What is GAGS made up of?
Repeating disaccharides of glucoronic OR iduronic acid
+
N-acetylglucosamine OR N-acetylgalactosamine
What is formed when GAGS chains are covalently linked to proteins?
Proteoglycans
What is there variation in that enables many types of connective tissue?
> relative proportion of fibres to cells in ECM
no. & proportion of diff cell types in ECM
proportion & arrangement of fibres in ECM
composition of non-ferrous component of ECM
What are the 3 main cell types?
Fibroblasts
Macrophages
Mast cells
What are the 4 specialised cell types?
> osteocytes (bone)
chondrocytes (cartilage)
adipocytes (adipose/fat)
blood cells
What was different in the ‘rubber skin man’?
Collagen not properly assembled
- doesn’t resist tensile force
(Elastin = good as skin springs back to normal)
What were the 2 possible causes of the ‘rubber skin man’s’ condition?
Failure of conversion of lysine to hydroxylysine by lysol hydroxylase
OR
failure to cleave off propeptide termini
–> fibrils & fibres don’t form
Which cell type is found in areolar connective tissue?
What fibre types are found in the tissue?
Fibroblast
Elastin
Collagen
What cell type is found in adipose tissue?
Which fibre type is found in the tissue?
Adipocytes
Reticular fibres
Which cell type is found in tendons & ligaments?
Which fibre type is found in the tissue?
How are the fibres orientated?
Fibroblast
Collagen
Parallel orientation along the line of force
Which cell type is found dermis of skin & organ joint capsules?
Which fibre type is found in the tissues?
Fibroblast
Collagen
Which cell type is found in elastic cartilage?
Which fibre type is found in the tissue?
Chondrocyte in lacuna
Elastin
Which cell type is found in bone?
Osteocytes in lacuna
Give examples of conditions where there are defects in the ECM
Scurvy
Fibrodysplasia ossificans progressiva
What are the causes of scurvy?
Vitamin C deficiency
–> defective collagen synthesis
Why is Vit C essential for collagen synthesis?
Vit C = cofactor for propyl hydroxylase
–> forms hydroxyproline
= stabilises triple stranded collagen
What are the symptoms of Scurvy?
Skin fragility & bleeding
Tooth loss
(Due to lack of normal fibrils)
What does Fibrodysplasia ossificans progressiva cause?
Muscle & connective tissue (e.g. tendons) gradually replaced by bone
