Extracellular matrix

Question 1

What is the ECM?

Answer 1

Any substance produced by cells & secreted into the extracellular space within the tissues

Question 2

Why is the ECM important?

Answer 2

> 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

Question 3

Describe the structure of connective tissue

Answer 3

Scattered cells e.g. fibroblasts

Predominantly ECM

Question 4

Describe the composition of ECM in connective tissues

Answer 4

Collagen fibres cross-linked by accessory proteins in a matrix of proteoglycans

Question 5

What are proteoglycans?

Answer 5

Proteins bound to polysaccharides

Question 6

Describe the structure of epithelial tissues

Answer 6

Layers of cells bound closely to form protective sheets

Minimal ECM

Question 7

Describe ECM in epithelial tissues

Answer 7

concentrated under epithelia (basal lamina)

- provides base for cells to sit on & acts as molecular sieve & substrate for migrating cells

Question 8

Describe the composition of ECM in plants

Answer 8

Cellulose fibres cross-linked w/ hemicellulose in matrix of highly branched polysaccharides

Question 9

Describe how ECM is arranged in plants

Answer 9

All plant cells surrounded by ECM

= cell wall

Question 10

What are cellulose fibres analogous to?

Answer 10

Collagen fibres

Question 11

How does the ECM differ between plants & animals?

Answer 11

Plant ECM contain polysaccharide fibres

Animal ECM contains fibres made of protein
- collagen & elastin

Question 12

What is the function of collagen?

Answer 12

Resists tensile force

Question 13

How many different collagen genes are there in mammals?

Answer 13

42

Question 14

How are collagen fibres formed?

Answer 14

1. 3 single-stranded collagens cross-link
   = collagen fibrils
2. Collagen fibrils link to form collagen fibres

Question 15

In what orientation are collagen fibres organised?

Answer 15

In 2 orthogonal directions

= 90 degrees to each other

Question 16

Give an example of a fibril forming collagen

Answer 16

Type II collagen

Question 17

Give an example of a cross-linking collagen

Answer 17

Type IX collagen

- has a kink in molecule so can bind along the side of 2 fibres at diff angles

Question 18

What is the function of elastin?

Answer 18

Provides tissues with elasticity

Question 19

What is elastin composed of?

Answer 19

Large filaments w/ lots of random spring-like coils

Question 20

What is elastin cross-linked by?

Answer 20

Lysine

Hydroxylysines

Question 21

How is the ECM in plants similar to in animals?

Answer 21

Matrix consists of polysaccharides

Plants: pectin (forms hydrated gel)

Animals: glycosaminoglycans = GAGS
(e.g. hyaluronan)

Question 22

What are the features of GAGS?

Answer 22

> highly -ve charge
hydrophilic
linked to proteoglycans

Question 23

Why is a -ve charge in GAGS significant?

Answer 23

Carboxyl group creates
 -ve charge
--> attracts water
= swells up 
= cushioning affect

Question 24

What is GAGS made up of?

Answer 24

Repeating disaccharides of glucoronic OR iduronic acid
+
N-acetylglucosamine OR N-acetylgalactosamine

Question 25

What is formed when GAGS chains are covalently linked to proteins?

Answer 25

Proteoglycans

Question 26

What is there variation in that enables many types of connective tissue?

Answer 26

> 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

Question 27

What are the 3 main cell types?

Answer 27

Fibroblasts Macrophages Mast cells

Question 28

What are the 4 specialised cell types?

Answer 28

> osteocytes (bone) > chondrocytes (cartilage) > adipocytes (adipose/fat) > blood cells

Question 29

What was different in the 'rubber skin man'?

Answer 29

Collagen not properly assembled - doesn't resist tensile force (Elastin = good as skin springs back to normal)

Question 30

What were the 2 possible causes of the 'rubber skin man's' condition?

Answer 30

Failure of conversion of lysine to hydroxylysine by lysol hydroxylase OR failure to cleave off propeptide termini --> fibrils & fibres don't form

Question 31

Which cell type is found in areolar connective tissue? What fibre types are found in the tissue?

Answer 31

Fibroblast Elastin Collagen

Question 32

What cell type is found in adipose tissue? Which fibre type is found in the tissue?

Answer 32

Adipocytes Reticular fibres

Question 33

Which cell type is found in tendons & ligaments? Which fibre type is found in the tissue? How are the fibres orientated?

Answer 33

Fibroblast Collagen Parallel orientation along the line of force

Question 34

Which cell type is found dermis of skin & organ joint capsules? Which fibre type is found in the tissues?

Answer 34

Fibroblast Collagen

Question 35

Which cell type is found in elastic cartilage? Which fibre type is found in the tissue?

Answer 35

Chondrocyte in lacuna Elastin

Question 36

Which cell type is found in bone?

Answer 36

Osteocytes in lacuna

Question 37

Give examples of conditions where there are defects in the ECM

Answer 37

Scurvy | Fibrodysplasia ossificans progressiva

Question 38

What are the causes of scurvy?

Answer 38

Vitamin C deficiency | --> defective collagen synthesis

Question 39

Why is Vit C essential for collagen synthesis?

Answer 39

Vit C = cofactor for propyl hydroxylase --> forms hydroxyproline = stabilises triple stranded collagen

Question 40

What are the symptoms of Scurvy?

Answer 40

Skin fragility & bleeding Tooth loss (Due to lack of normal fibrils)

Question 41

What does Fibrodysplasia ossificans progressiva cause?

Answer 41

Muscle & connective tissue (e.g. tendons) gradually replaced by bone