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INFLAMMATION & REPAIR
Lecture 9 Repair, Fibrosis & Healing
Winter 2013
Chelsea Martin Special thanks to Drs. Hanna and Forzan
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REPAIR
• Definition = process by which lost or necrotic cells are replaced by vital cells
• involves regeneration &/or fibrosis.
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REPAIR – by Regeneration
• replacement of cells by those of an identical type
• requires: - tissue capable of parenchymal regeneration
- maintenance of the architectural (CT) framework/ basement membranes
eg, Parvoviral enteritis
• necrosis of intestinal epithelium (crypts)
• regeneration of epithelium = recovery
Note: not all animals survive to see this
regeneration!
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• repair starts early in the inflammatory process
• mediators often both pro-inflammation and pro-repair
REPAIR – by Regeneration
Fig. 9-11 Normal and injured mucosa, nasal conchae, rats. Normal ciliated epithelium composed of tall columnar cells with numerous cilia. Day 1. Nasal
epithelium following exposure to air containing an irritant gas (hydrogen sulfide). Note detachment and exfoliation of ciliated cells, leaving a denuded basement
membrane (arrows). This same type of lesion is seen in viral or mechanical injury to the mucosa of the conducting system. Two days after exposure, the
basement membrane is lined by rapidly dividing preciliated cells, some of which exhibit mitotic activity (arrow). Ten days after injury, the nasal epithelium is
completely repaired. H&E stain.
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REPAIR – by Fibrosis
• when replacement by original tissue is impossible
• see increase in fibrous CT within the tissue
fibroblasts synthesize collagen & proteoglycans
• new blood vessels are necessary (neovascularization)
• granulation tissue = fibroblasts / collagen & neovascularization
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Disorganized, early-stage, granulation tissue
Organized, maturing, granulation tissue
REPAIR – by Fibrosis Granulation tissue
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ability of the host to eliminate the inciting agent
how much tissue damage / necrosis (CT framework, basement
membranes)
how much of the exudate is removed / resolved
nature of injured cells (labile / stable vs permanent)
REPAIR – Regeneration vs Fibrosis
• since so many requirements for a return to normality, some degree of scarring
is more common than complete resolution for most significant lesions
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Tissue Proliferative Capability
• Labile (continuously dividing)
• Stable (quiescent)
• Permanent (non-dividing)
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Labile Cells - usually repairs by regeneration
• Continuously dividing
• after injury (if not severe) see rapid regeneration.
• >1.5% cells in mitoses
Examples:
Skin / mucosal epithelium
Lymphoid Cells
Hematopoietic Cells
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Stable Cells – repair by regeneration &/or fibrosis
• low level of replication
<1.5% of normal adult cells in mitosis
• can rapid divide in response to injury
Examples:
Hepatocytes
Renal tubular epithelium
Endothelium
Mesenchymal cells (fibroblasts)
Smooth muscle cells
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Need intact basement membranes for renal
tubules or hepatocytes to regenerate.
Glomeruli do not regenerate.
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Permanent Cells – repair by fibrosis
• Cells don’t divide
• No regenerative ability
• 0.0% cells are in mitoses
Examples: Neurons Cardiac myocytes Lens epithelium
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Repair by Fibrosis
Timeline:
• begins within 24 hours of injury!
• fibroblasts & endothelial cells migrate to the site of injury & proliferate
• 3-5 days see early granulation tissue (fibroblasts / collagen & neovascularization)
• wks to months see collagen and decreased vessels (scarring)
Figure 3-21 (Robbins) A, Granulation tissue showing numerous blood vessels, edema, and a loose ECM containing occasional
inflammatory cells. Collagen is stained blue by the trichrome stain; minimal mature collagen can be seen at this point. B,
Trichrome stain of mature scar, showing dense collagen, with only scattered vascular channels.
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Fibrosis Repair by Connective Tissue Replacement
4 components
1) Angiogenesis (neovascularization)
2) Migration & proliferation of fibroblasts
3) Deposition of extracellular matrix
4) Maturation and reorganization of fibrous tissue
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1) Angiogenesis
VEGF
Figure 3-15A In angiogenesis
from preexisting vessels,
endothelial cells from these vessels
become motile and proliferate to
form capillary sprouts. Regardless
of the initiating mechanism, vessel
maturation (stabilization) involves
the recruitment of pericytes and
smooth muscle cells to form the
periendothelial layer.
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2) Migration/Proliferation of Fibroblasts
• starts within 3-5 days; esp due to TGF-β & PDGF
3) Deposition of ECM (mainly collagen)
• due to growth factors: PDGF, TGF-β, FGF
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• development of granulation tissue and subsequent scar tissue formation
4) Maturation and reorganization of fibrous tissue
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Wound Healing
• process of fibrous replacement and
regeneration (varying amounts of each)
• results in restoration of tissue
continuity, with or without function.
The Wound Man, 16th century http://images.wellcome.ac.uk/
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Wound Healing
1. Injury → inflammation (necrosis)
2. Parenchymal cells regenerate (if possible)
3. Migration/proliferation
fibroblasts & endothelial cells
parenchymal cells
4. Synthesis of ECM (collagen / proteoglycans)
5. Remodeling of parenchymal cells
(restore function)
6. Remodeling of connective tissue
(wound strength)
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What might impair Wound Healing?
• infection
• nutrition
• glucocorticoids
• mechanical factors
• poor perfusion
• foreign bodies
• type & amount of tissue injured
• location of injury
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Cutaneous Wound Healing by First Intention
• possible when tissue elements in close
proximity (eg surgical wound).
• a primary union where regeneration
predominates over fibrosis
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24 hours
• neutrophils migrate into fibrin clot
• basal epidermal cells at edges increase mitotic activity
Cutaneous Wound Healing by First Intention
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24-48 hours
• epithelial cells migrate and proliferate
• deposition of basement membrane
Cutaneous Wound Healing by First Intention
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Day 3 • macrophages replace neutrophils
• fibroblasts & collagen fibers at margins (vertical)
• epithelial cells continue to proliferate
Day 5 • neovascularization peaks
• collagen fibers bridge wound (horizontal)
Cutaneous Wound Healing by First Intention
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Day 14
• fibroblasts and collagen accumulation continue
• decreased leukocytes & edema
• vascular channels regress
Cutaneous Wound Healing by First Intention
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4 weeks
• scar (fibroblasts and collagen)
• few inflammatory cells
• tensile strength increases with time
Cutaneous Wound Healing by First Intention
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• where there is poor apposition (eg ragged cuts)
• more complex repair process
more inflammation (fibrin & leukocytes)
more granulation tissue
contraction due to myofibroblasts
often an irregular scar
Cutaneous Wound Healing by Second Intention
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3-7 days 24 hrs
(weeks)
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Figure 3-20 (Robbins) Healing of skin ulcers.
The histologic slides show: B, a skin ulcer with a
large gap between the edges of the lesion; C, a thin
layer of epidermal re-epithelialization and extensive
granulation tissue formation in the dermis; and D,
continuing re-epithelialization of the epidermis and
wound contraction
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Wound Strength
• immediate (if sutured) ~70%
• if not sutured:
1 week ~10%
3 months ~ 70-80%
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Granulation tissue
• pink, soft, granular tissue on wound surface
• histologically see proliferation of new small blood vessels and fibroblasts
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Granulation tissue
Red fox with snare injury, 3 weeks duration
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Granulation Tissue (4 zones)
1) Necrotic debris and fibrin
2) Zone of macrophages and
in-growing capillaries
3) Zone of capillary and
fibroblast proliferation
4) Zone of fibrous connective
tissue
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Exuberant Granulation Tissue “Proud Flesh”
• due to:
severe and prolonged tissue injury
loss of tissue framework (BM’s)
large amounts of exudate
• hypertrophic scar – precludes epithelization
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• humans can also get exuberant
granulation tissue
• one type is called keloid = excessive
amount of scar tissue that grows beyond
the boundaries of the original wound and
does not regress.
Exuberant granulation tissue
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Fibrosis and/or Exuberant Granulation Tissue Consequences
• loss of functional parenchymal tissue
• alteration of physical properties of tissue
skin with scar more prone to tearing
pulmonary fibrosis decreases compliance
requiring more respiratory effort.
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Repair in Specific Tissues
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HEALING - LIVER
• healing can vary from complete
parenchymal regeneration to
extensive scar formation
• depends on how much damage to
the CT framework
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HEALING - LIVER
• healing can vary from complete
parenchymal regeneration to
extensive scar formation
• depends on how much damage to
the CT framework
Fibrosis (blue areas)
Nodules of proliferating / regenerating
hepocytes (ie nodular hyperplasia, red
areas); these nodules representing
hepatocytes trying to regenerate in liver with
damaged CT framework
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HEALING - KIDNEY
• variable regenerative capacity
cortical tubules – good
medullary tubules – minimal
glomeruli - none
• note, tubular regeneration requires intact BM’s
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HEALING - KIDNEY
Normal Chronic interstitial nephritis with fibrosis
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HEALING - LUNG
• Alveoli with intact BM’s
regenerate by type 2 pneumocyte
• Unresolved exudate
organized by fibrosis
• Alveoli with damaged BM’s
fibrosis / scarring
Chronic inflammation in the lung:
1) chronic inflammatory cells (*)
2) Destruction of parenchyma, ie normal type 1
pneumocytes replaced by type 2 pneumocytes
(arrowheads)
3) Replacement by fibrous connective tissue
(black arrows)
* Normal alveoli
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Heart, cougar. Myocardial
abscesses (mycotic infection)
Q: If cougar had lived, how
would repair occur?
A: by fibrosis (myocardial scarring)
HEALING - HEART
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HEALING - BRAIN
• Fibroblasts and glial cells proliferate along vasculature
neurons are permanent cells – can’t proliferate / regenerate
astrocytes & fibroblasts proliferate – form fibrous network
microglial cells are phagocytic - clean up debris
Pig brain: Cerebellar abscess with associated cerebellar atrophy
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BONE REPAIR - STAGES
Hematoma – 1-2 days
Inflammatory phase – up to 7 days
Reparative phase – wk 1 to many wks
Remodeling phase – several wks to months
soft callus = organizing fibrocellular
tissue before calcification.
hard callus = hard bony tissue that
develops around the ends of
fractured bone during healing
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BONE REPAIR - Callus
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INFLAMMATION & REPAIR
The End!
Chelsea Martin Special thanks to Drs. Hanna and Forzan