Postgraduate

1. HEALING AND REPAIR
Post graduate

2. Objectives
By the end of this session every student should be able to:
Describe healing processes and cell cycle
Describe growth factors and their functions
Describe factors affecting wound healing and its complications.

3. Outline
Introduction
Cell cycle and Growth factors
Stages of healing
Healing in specialized tissues
Factors affecting healing
Complications of wound healing

4. INTRODUCTION
Healing
– is the body response to injury in an attempt to restore normal
structure and function.
– Ability of the body to repair from tissue insultations and effects
of inflammation.
– Inflammatory process is also the crucial stage in tissue healing

5. INTRODUCTION CONT’S
It occurs by two types of process:
Regeneration
Scar formation/Repair
Regeneration: Is proliferation of residual (uninjured) cells that retain the
capacity to divide, and by replacement from tissue reserve cells.
Results in complete restoration of original tissues.
Scar formation/repair: Occurs by the laying down parenchymal and
connective (fibrous) tissue.
At some time they occur simultenously

6. CELL AND TISSUE REGENERATION
• The regeneration of injured cells and tissues involves cell
proliferation, which is driven by growth factors and is critically
dependent on the integrity of the extracellular matrix.
• The key processes in the proliferation of cells are DNA
replication and mitosis. The sequence of events that control
these two processes is known as the cell cycle

7. CELL AND TISSUE REGENERATION
Cell numbers can be altered by increased
or decreased rate of
Stem cell input,
Cell death via apoptosis, or
Changes in the rates of proliferation or
differentiation

8. CELL CYCLE
Period between two successive cell divisions is divided into 4
unequal phases.
G0 (gap 0) phase: This is the quiescent or resting phase of
the cell after an M phase.
G1 (gap 1) phase: The daughter cell enters G1 phase after
mitosis.
S (synthesis) phase: During this phase, the synthesis of
nuclear DNA takes place.
G2 (gap 2) phase: After completion of nuclear DNA
duplication, the cell enters G2 phase.
M (mitosis) phase: Phase of mitosis.

9. CELL CYCLE

10. Depending upon their capacity to divide, the cells of
the body can be divided into 3 groups:
1. Labile (continuously dividing) tissues.
These include hematopoietic cells in the bone marrow
and epithelia.
2. Stable tissues.
Cells of these tissues are quiescent state, they include
parenchyma of solid tissues, such as liver, kidney, and
pancreas.
3. Permanent cells
These cells lose their ability to proliferate around the
time of birth. These include: neurons of nervous
system, skeletal and cardiac muscle cells.

11. Requirements for Healing Process
1. Growth factors
Major activity is to stimulate the function of
growth control genes, many of which are
called proto-oncogenes because mutations in
them lead to unrestrained cell proliferation
characteristic of cancer (oncogenesis)

12. Growth factors for regeneration and
repair
Growth Factor Source Functions
Epidermal growth
factor(EGF)
Activated macrophage
,salivary gland,
keratinocytes and other
many cells
Mitogenic for keratinocytes
and fibroblast stimulates
keratinocytes migration
,formation of granulation
tissues,
Platelate derived growth
factor (PDGF)
Platelates,macrophages,
endothelial cells,smooth
muscles cell and
keratinocytes.
Chemotactic for neutrophil
macrophages fibroblast and
smooth muscles cells.
Activate and stimulates
proliferations of fibroblasts,
endothelia and others cells.
Vascular endothelia growth
factor (VEGF)
Mesenchymal cell Stimulate proliferation of
endothelia cells and
increase vascular
permiability

13. Growth factor Source Functions
Trans forming growth
factors α (TGF-α)
Activated macrophages,
keratinocytes ,many other
cells
Stimulates proliferation of
hepatocytes and many other
epithelial cells
Transforming growth
factorβ (TGF-β)
Platelates ,macrophages, T-
lymphocytes, endothelial
cells smooth muscle cells,
Fibroblast cells
Chemotactic for fibroblast
and leucocytes, stimulates
ECM protein thynthesis
and suppress acute
imflammation
Keratinocytes growth
factor (KGF)
Fibroblasts Stimulates keratinocytes
migration ,proliferation and
differentiation
Fibroblast growth factor
(FGF ) including (FGF 1
acidic and basic(FGF 2)
Macrophages Mast cells ,
endothelial and other many
types
Chemotactic and mitogenic
for fibroblast stimulates
angiogenesis and ECM
protein syntyhesis

14. Requirements for Healing Process Cont..
2. Extracellular Matrix
The ECM is a complex of three dimension several proteins,
fibers and molecules that assembles into a network that
surrounds cells and constitutes a significant proportion of any
tissue.
Tissue repair depends not only on growth factor activity but
also on interactions between cells and ECM components.

15. Components of the Extracellular Matrix
There are three basic components of ECM:
1. Fibrous structural proteins such as collagens and elastins,
which confer tensile strength and recoil;
2. Water-hydrated gels such as proteoglycans and hyaluronan,
which permit resilience and lubrication; and
3. Adhesive glycoproteins that connect the matrix elements to
one another and to cells

16. • In adult humans, optimal wound healing
involves the following the events:
(1) rapid hemostasis;
(2) appropriate inflammation;
(3) mesenchymal cell differentiation,
proliferation, and migration to the wound site;

17. Functions of the ECM
Mechanical support for cell anchorage, cell migration, and
maintenance of cell polarity
Control of cell proliferation
Scaffolding for tissue renewal. An intact ECM is required for
tissue regeneration, and if the ECM is damaged, repair can be
accomplished only by scar formation.
Establishment of tissue microenvironments.

18. STAGES OF WOUND HEALING
Although wound healing occurs on a time continuum, division of
the process into stages allows for ease description and evaluation.
These include:
1. Hemostasis
2. Inflammation
3. Proliferation and migration
4. Remodeling and maturation

19. 1. Hemostasis
It begins immediately after wounding, with vascular constriction and
fibrin clot formation.
It’s mechanisms include:
1. Vascular constriction,
2. Formation of a platelet plug,
3. Formation of a blood clot (fibrin) as a result of blood coagulation,
and
4. Fibrin acts as scaffold on which fibroblast, endothelial cells etc,
move into a defect.

21. • The clot and surrounding wound tissue release
pro-inflammatory cytokines and growth
factors such as transforming growth factor
(TGF)-β, platelet-derived growth factor
(PDGF), fibroblast growth factor (FGF), and
epidermal growth factor(EGF).
• Once bleeding is controlled, inflammatory
cells migrate into the wound (chemotaxis) and
promote the inflammatory phase

22. 2. Inflammation
• Platelet activation is followed by an influx of inflammatory
cells within the first 1 to 2 days, led by PMN
• Neutrophils, as well as monocytes, fibroblasts, and endothelial
cells, deposit on a fibrin scaffold formed by coagulation system.
• These PMNs are the major source of proinflammatory
cytokines, such as IL-1α, IL-1β, IL-6, and TNF-α, and exert
cascades of inflammatory reactions and prevent infection.

24. 3. Proliferation
Is a broad term for a group of key steps that occur during this
phase. Although they begin at various time periods in wound
healing, collectively,
Angiogenesis and granulation tissue formation
Collagen deposition.
Re-epithelialization.

25. Angiogenesis
• The process of new blood vessel development from existing
vessels, primarily venules and the fibrin.
• Initiated on day 2 of post wounding and stimulated by VEGF,
FGF, angiopoietins, and Transforming Growth Factor-β

27. Process involves;
• Vasodilation in presence of NO
• Basement membrane degradation of the parent
vessel occurs and formation of capillary
sprout.
• Directional migration toward the stimulus
• Proliferation of the endothelial cells behind the
leading edge of stimulus
• Remodeling into capillary tube formation.

28. • Maturation by recruitment of periendothelia cells, (pericyte
for capillaries and smooth muscle cell for larger vessels)
• Suppression of endothelial proliferation and migration and
deposition of the basement membrane
NB; growth factors involved; VEGF,FGF(1&2),Angiopoetins
1&2, PDGF, TGF-beta

29. • The newly formed vessels are leaky, and this leak contributes to
the edematous appearance of tissue undergoing repair.
• As healing is completed, the nonfunctional vessels are
degraded, leaving few blood vessels in mature scar tissue.

30. Granulation tissue formation
• The tissue formed has an appearance of a reddish granular layer
and is therefore referred to granulation tissue
• Histologically the main cellular components of granulation
tissue are endothelial cells and the fibroblasts, although some
inflammatory cells are also commonly present

31. Collagen synthesis & ECM formation
• As healing progresses, fibroblast and new vessel proliferation
decreases, ECM deposition and collagen synthesis increases.
• Eventually the granulation tissue is covered by a scar largely
composed of dense collagen, inactive fibroblasts and fragments
of elastic materials
• TGBbeta, PDGF, cytokine (IL-1,IL-13)

32. Re-epithelialization:
Is wound recovery with new epithelium and consists in both
migration and proliferation of keratinocytes from the lesion
periphery.
These events are regulated by three main agents: growth factors,
adhesion molecules and enzymes.

33. 4. Remodeling
• Transition from granulation tissue to scar involves shifts in the
composition of the extracellular matrix
• Even after its synthesis and deposition, scar ECM continues to
be modified and remodeled
• Can take years as the skin first produces collagen fibers, which
are broken down and rearranged to withstand stress

34. PHASE CELLULAR AND BIO-PHYSIOLOGIC EVENTS
HAEMOSTASIS 1. Vascular constriction
2. Platelet aggregation, degranulation, and fibrin formation (thrombus)
INFLAMMATION 1. Neutrophil infiltration
2. Monocyte infiltration and differentiation to macrophage
3. Lymphocyte infiltration
PROLIFERATION 1. Angiogenesis
2. Re-epithelialization and granulation tissue formation
3. Collagen synthesis
4. Extracellular matrix formation
REMODELLING 1. Collagen remodeling
2. Vascular maturation and regression

36. Selected clinical example of wound healing.
Healing of skin wounds provides a classical example of
combination of regeneration and repair which can be
accomplished in one of the following two ways:
a) Healing by first intention (primary union)
b) Healing by second intention (secondary union)

37. Healing by First Intention
This is defined as healing of a wound which has the following
characteristics:
Clean and uninfected;
Surgically incised;
Without much loss of cells and tissue;
Edges of wound are approximated by surgical sutures.

38. • 24hrs ; neutrophil migrates towards the fibrin clot, there is
mitotic activity is increased at the basal cells
• 48hrs epithelial cell starts to proliferate towards to the wound,
from both edges- re-epithelialization occurs
• 3rd day; neutrophils are replaced by macrophages, granulation
tissue invades the gap, collagen deposition begins no bridging
• 5th day; neovascularization peaks and granulation fills the gaps,
collagen starts bridging the incision

39. • 2nd week; angiogenesis and granulation significantly decreases,
fibroblast proliferation and collagen synthesis increases.
• 1 month; no inflammatory cells, normal epidermis has forms,
but the appendages are lost permanently. There is cellular
connective tissue

40. Healing by Second Intention
This is defined as healing of a wound having the following
characteristics:
Open with a large tissue defect, at times infected;
Having extensive loss of cells and tissues; and
The wound is not approximated by surgical sutures and is left
open.

41. • With extensive tissue injury, inflammation is more intense
• There is abundant and exuberant granulation tissue which
impedes epithelialization . Also result in greater mass of scar
formation
• There is wound contraction as a result of myofibroblasts from
the excessive granulation

43. FACTORS AFFECTING WOUND HEALING
Local Factors
• Local infection
• Blood supply (perfusion & oxygenation)
• Foreign bodies (including sutures)
• Mechanical stress
• Type of tissue, size and location of injury
• Ionizing radiation - delays granulation tissue formation

44. Factors affecting wound healing cont...
Systemic Factors
• Age (poor blood supply in aged and debilitated)
• Nutrition ( Protein, vitamin C, zinc, magnesium)
• Systemic infection
• Diabetes
• Smoking (nicotine, CO, hydrogen cyanide)
• Drugs (steroids, cytotoxic medications, intensive antibiotic
therapy)

45. COMPLICATION OF WOUND HEALING
• Can arise from abnormalities in any of the basic components of
the repair process.
• These aberrations can be grouped into three general categories:
1.Deficient scar formation
2.Excessive formation of the repair components
3.Formation of contractures.

46. 1. Defects in healing: chronic wounds
• Venous ulcers: due to chronic venous hypertension. Fail to heal because
of poor delivery of oxygen
• Arterial ulcers: in individuals with atherosclerosis of peripheral arteries -
> ischemia-> atrophy and necrosis of skin and underlying tissues.
• Pressure sores: skin ulceration and necrosis of underlying tissues due to
prolonged compression of tissues against a bone
- lesions caused by mechanical pressure and local ischemia
• Diabetic ulcers : Tissue necrosis and failure to heal are the result of small
vessel disease causing ischemia, neuropathy, systemic metabolic
abnormalities, and secondary infections.

49. Defects in healing cont...
Dehiscence (wound rupture)
• Most frequently after abdominal surgery
• A result of increased abdominal pressure

50. Complications of wound healing cont...
2. Excessive formation of the repair components
• Accumulation of excessive amounts of collagen may give
rise to a raised scar- hypertrophic scar
• If the scar tissue grows beyond the boundaries of the original
wound and does not regress- Keloid
• Exuberant granulation/ proud flesh- formation of excessive
granulation tissue which protrudes above the level of the
surrounding skin and blocks reepithelialization.

51. Complications of wound healing cont...
Hypertrophic scar Keloid

52. Proud flesh

53. Complications of wound healing cont...
3. Contractures
• Wound size contraction is a normal healing process.
• Exaggeration leads to contractures
• Common in palms, soles, anterior aspect of the thorax
• Can compromise joint movement

54. Contracture

55. Other complications of wound healing
4. Neoplasia
• Scar may be site of
development of carcinoma
(rare)
Eg; Marjolin’s ulcer -
Squamous cell carcinoma
arising from burn wound.
-Takes 15-20 years to
develop at the site of
injury.

56. References
Harsh Mohan Pathology Text Book 6th Edition
Robbins textbook of Pathology 9th Edition