Week 5: Connective Tissue 2 - Properties and Extracellular Matrix

Question 1

What types of fibres are in CT?

Answer 1

Collagen, fibres and reticular

Question 2

What are the morphological characteristics of collagen?

Answer 2

• Thickest fibre
• Each collagen fibre is composed of many collagen fibrils
• Fibrils cause a banding pattern in fibres formed
• Can form networks/ sheets
• Tropocollagen –> collagen bundles

Question 3

Describe the formation of collagen.

Answer 3

Collagen is a family of proteins that have alpha chain (polypeptide) subunits that interact in various ways to form fibrilar collagens (fibrils –> fibres –> fibre bundles), network or sheet forming collagens in basal laminae, and linking and choring collagens (link fibrillar collagens to each other and ECM)
Formation begins with intracellular synthesis in fibroblasts.
RER:
- Synthesis of procollagen alpha chains with propeptides at each end
- Hydroxylation and attachment of sugars to chains
- Assembly of chains into triple helix procollagen molecule (soluble)
Golgi:
- Packaging of procollagen into secretory vesicles
- Exocytosis of procollagen into extracellular space
Extracellular modification
- Cleavage of terminal proppeptides by procollagen peptidases; soluble procollagen –> insoluble tropocollagen molecules
- Tropocollagen molecules aggregate to form collagen fibrils
- Fibrils reinforced by covalent cross-links between molecules

Question 4

What are the properties of collagen?

Answer 4

• Extremely tough: resistant to normal shearing and tearing forces
• High tensile strength
• White when abundant, e.g., old scar, fresh tendons
• LM appearance: acidophilic (pink) fibres and fibre bundles

Question 5

What does the type of collagen depend on?

Answer 5

Amino acid sequence of tropocollagen varies and hence the amount of polymerisation varies.

Question 6

What is the structure of collagen type I?

Answer 6

Fibrils, fibres and bundles

Question 7

Where is collagen type I found?

Answer 7

Most CT has collagen type I, e.g., dermis, tendons, ligaments, bone, dentin

Question 8

What is the function of collagen type I?

Answer 8

Provides resistance to stress and tension; enables flexibility (movement) within tissue.

Question 9

What is the structure of collagen type II?

Answer 9

Fibrils only

Question 10

Where is collagen type II found?

Answer 10

Cartilage

Question 11

What is the function of collagen type II?

Answer 11

Provides resistance to pressure

Question 12

What is the structure of collagen type III?

Answer 12

Fibrils and fibres

Question 13

Where is collagen type III found?

Answer 13

Reticular fibres, cellular organs

Question 14

What is the function of collagen type III?

Answer 14

Provides delicate flexible framework

Question 15

What is the structure of collagen type IV?

Answer 15

Network sheet

Question 16

Where is collagen type IV found?

Answer 16

Basal lamina

Question 17

What is the function of collagen type IV?

Answer 17

Support of delicate structures, filtration

Question 18

What vitamin deficiency can inhibit collagen production?

Answer 18

Vitamin C

Question 19

How does a vitamin C deficiency cause scurvy?

Answer 19

Collagen has high levels of proline and lysine amino acids that undergo post-translational modification in RER to hydroxyproline and hydroxylysine.
vitamin C needed for activation of enzymes to modify proline and lysine to hydroxyproline and hydroxylysine.
Lack of vitamin C causes scurvy where there is a reduced amount of collagen that is also less stable
Tissues that have high turnover of collagen (periodontal ligaments) are severely affected, causing loosening of teeth.

Question 20

Describe the properties of reticular fibres.

Answer 20

• Form a flexible delicate support for cellular organs, e.g., spleen, bone, marrow, lymph nodes
• Special dyes needed to show reticular fibres clearly in LM
• Form an additional layer; reticular lamina below some basal laminae

Question 21

Describe the general properties of elastic fibres?

Answer 21

• Elasticity
• Taut (i.e., straight and tight) in tissues
• Branch
• Thinnest fibres

Question 22

Describe the distribution of elastic fibres.

Answer 22

• Large (elastic) arteries, e.g., aorta: passive stretch and recoil, which propels blood onwards and acts as a pressure
• Skin
• Lungs
• Passive stretch and recoil

Question 23

Describe the composition of elastic fibres.

Answer 23

• Elastin molecules are cross-linked with each other
• When relaxed: random coiled structure
• When stretched: elongated

Question 24

What is the composition of AGS.

Answer 24

• Carbohydrate and protein components: these complex together
• Glycoproteins: globular protein molecules to which branched chains of monosaccharides are covalently attached, bind components together, influence their interactions
• Proteoglycans: protein core with up to 200 glycosaminoglycans (GAGs, strong negative charge), which attract water to form solvation water

Question 25

What are the functions of AGS?

Answer 25

- Transportation of substances through CT: contains solvation water - Restricts penetration by bacteria etc.: viscosity acts as a defence mechanism - Mega molecules support cells and fibres

Question 26

What is oedema?

Answer 26

Abnormal accumulation of interstitial fluid