9 - Pathogenesis of Fibrosis Flashcards
(42 cards)
Two processes by which repair of injured tissue occurs
- Regeneration
- Scarring
Regeneration
- Growth of cells and tissues to replace lost/damaged structures
- Restoration of normal cells and cell function
Scarring
- Occurs in response to a wound, inflammation, necrosis
- Organs not able to regenerate
- Deposition of connective tissue
- ECM framework damaged
What are factors influencing repair of injured tissue based on
- Intrinsic capacity of cells within a tissue to proliferate (or presence of stem cells)
- Labile, stable or permanent tissue
Labile
- Continuously dividing cells
- e.g. Columnar epithelium GI
tract or hematopoietic cells in bone marrow
Stable tissue
- Quiescent cells (G0) that proliferate following damage
- e.g. parenchymal cells in liver
Permanent tissue
- Terminally differentiated cells
- eg. Cardiac myocytes in heart
Examples of factors influencing repair of injured tissue
- Extent of tissue damage
- Location of injury damage
- Duration of injurious agent
- Infection (delays healing, prolongs inflammation)
- Poor perfusion
- Mechanical stress
Requirements of regeneration
- Intact tissue scaffold
- Approptiate stem cells to be intact
Aberrant wound healing response
Fibrosis
Fibrosis
- Formation of excessive fibrous tissue
- Can adversely affect functional capacity
- eg. fibrosis following MI - compromised contractile function
Regulation of healing and repair
- Controlled by biochemical factors released in response to cell injury, death or trauma
- Cell responses regulated by intracellular signalling
Function of biochemical factors released in response to cell injury cell death, or mechanical trauma
- inducing resting cells to enter
cell cycle - Balance of stimulatory or inhibitory factors (determines overall effect)
- Shorten cell cycle
- Decrease rate of cell loss
Autocrine
Targets self
Paracrine
Targets nearby
Endocrine
Targets distant
Cellular source of TGF-β
- Platelets
- T cells
- Macrophages
Targets of TGF-β
- Chemotactic for many cells
- Stimulates angiogenesis
- TIMP synthesis
ECM
Non cellular component within all tissues and organs
Interstitial matrix
- Spaces between epithelial, endothelial and smooth muscle cells
- Connective tissue
- Fibrillar and non fibrillar collagen
- Elastin, Fibronectin, proteoglycans, hyaluronate
Basement membrane
- Produced by epithelial and mesenchymal cells
- Associated with cell surface
- Amorphous non-fibrillar collagen (type IV)
- Laminin, heparan sulfate, proteoglycan, glycoproteins
Major source of ECM components
- Fibroblasts
- As repair continues, proliferation decreases, increased collagen deposition
- Collagen synthesis starts 3-5 days after injury
Granulation tissue in scarring
- Becomes the scar (scaffold)
- Spindle-shaped fibroblasts
- Dense collagen
- Elastic tissue fragments
What causes scar to become pale
Vascular regression