Wound Healing and Repair

Susan and Allison

Define the following cell types, give examples:

O Labile

O Stable

O Permanent

Continuously dividing- Epithelia e.g. Skin, GI, cervix,

urinary tract

Infrequent divisions but rapid if needed:- Liver, kidney, fibroblasts, smooth

muscle cells, endothelial cells, chondrocytes, osteocytes

Never divide in adult life- Cardiac muscle cells, nerve cells, skeletal muscle cells

What are the 3 main outcomes following tissue injury?

O RegenerationO Scarring

O What do we mean by each of the terms?

Restitution of the normal structure and function

Loss of function but structural stability restored

Difference between scar and fibrosis is exposure to stimuli (short term vs long term)

RegenerationO Definition: Restoration of normal

structure and functionO Can be restored as long as there is

minimal damage to tissue architecture and parenchyma cells can proliferate from residual stem cells

O 2 possible outcomes of regeneration...

RegenerationO 2 possible outcomes of regeneration:

1. ResolutionO Restoration of normal structure and functionO Need intact parenchyma or ability to produce

parenchymal cellsO Labile cells

2. Compensatory growthO Compensatory growth of cells to restore normal tissue

functionO Need intact architecture or ability to produce

parenchymal cellsO Stable cells

Fibrous repairO Definition: Healing by deposition of

connective tissue (scar)O Occurs when the parenchyma AND stroma

are damaged in labile or stable tissuesO Associated with loss of function of tissues

O What is the main problem with scar tissue?O It does not have the same tensile strength

that normal tissue has

What 3 main processes are involved fibrosis repair?

1. Inflammation O Macrophages clear out dead tissue

2. Granulation tissue O Angiogenesis,O Fibroblasts proliferate/migrate

3. Scar formation O Connective tissue remodelingO Recovery of tensile strength

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What are the 7 steps in cutaneous wound healing?

1. Formation of a blood clot2. Formation of granulation tissue3. Cell proliferation and collagen deposition4. Scar formation5. Wound contraction6. Connective tissue remodeling7. Recovery of tensile strength

What important factors are involved?

1. Formation of a blood clot (day 1)2. Formation of granulation tissue (day 3-5)

O Angiogenesis

3. Cell proliferation and collagen deposition (day 3-10)

4. Scar formation5. Wound contraction6. Connective tissue remodeling (day 15+)7. Recovery of tensile strength (3 months)

VEGF

TGF-β

PDGF and MMPs

What are the features of granulation tissue?

O Hallmarks:O AngiogenesisO Fibroblast proliferation

O Other features:O Inflammatory cellsO Oedema

Types of healing

O Primary intention:O Wound is artificially closed e.g.

stitches, graft

O Secondary intention:O Wound is not closed (spontaneous

healing)

Initial contractionEschar formsEpidermis regenerates at base

Granulation tissue bed

More contractionMore scarring

Takes longer than primary

What are the differences between primary and secondary intention healing? [6]

Loca

l Fa

ctors

• Infection prolongs inflammatory stage

• Mechanical factors

• Foreign bodies impairs fibrous repair

• Size of wound• Location of

wound• Type of wound

Syst

em

ic

Fact

ors• Metabolic Status

• Nutritional Status

• Hormones• Circulatory

status

What local factors influence wound repair? [6] What systemic

factors influence wound repair? [4]

What 3 main things can go wrong with repair?

1. Inadequate formation O Rupture O Ulceration

2. Excessive formationO Keloid – scar spreads outside the

boundary of the linesO Hypertrophic – excessive scar within

boundaries of woundO Proud flesh (granulation tissue)

3. Formation of contractureO Secondary intention healing may result in

excessive contracture