This document provides an overview of healing and repair processes. It describes the cell cycle and growth factors that drive proliferation during healing. The stages of healing - hemostasis, inflammation, proliferation, and remodeling - are outlined. Factors that affect wound healing like nutrition, infection, and drugs are also discussed. Complications from both deficient and excessive scar formation are mentioned. The goal is to describe cellular and tissue regeneration during injury response and restoration of structure and function.

1. HEALING AND REPAIR

2. Objectives
At the end of this session every student should
be able to:
To describe healing processes and cell cycle
To describe growth factors and their functions
To describe factors affecting wound healing
and its complications.
To describe recent researches and
developments in wound healing

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

4. INTRODUCTION
Healing - the body response to injury in an
attempt to restore normal structure and
function.
It occurs by two types of reactions:
Regeneration
Scar formation/Repair

5. INTRODUCTION CONT’S
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.

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.
Cells of these tissues are continuously being lost and
replaced by maturation from stem cells and by
proliferation of mature cells
These include hematopoietic cells in the bone marrow
and epithelia.

11. 2. Stable tissues.
Cells of these tissues are quiescent and have
only minimal replicative activity in their normal
state. However, these cells are capable of
proliferating in response to injury or loss of
tissue mass.
Stable cells constitute the parenchyma of most
solid tissues, such as liver, kidney, and pancreas.

12. • 3. Permanent cells
These cells lose their ability to proliferate
around the time of birth. These include: neurons
of nervous system, skeletal muscle and cardiac
muscle cells.

13. Growth Factors
Are proteins that stimulate the survival and
proliferation of particular cell and may also,
promote migrations, differentiation, and other
cellular response.
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)

14. Signaling Mechanisms of Growth Factor
Receptors
Most growth factors function by binding to
specific cell- surface receptors and triggering
biochemical signals in cells.
Signaling may occur;
Directly in the same cell that produces the
factors( Autocrine signaling)
Between adjacent cells (Paracrine signaling).
Over a great distance (Endocrine signaling)

16. Receptor Signaling
Class Ligands mechanism
Receptors with
intrinsic
tyrosine kinase
activity
EGF, VEGF, FGF, HGF
Activates tyrosine kinase on the
other chain, resulting in activation of
multiple downstream signaling
pathways and activation of various
transcription factors.
G protein
coupled
seven-
transmembrane
receptors
(GPCRs)
Multiple inflammatory
mediators,
Hormones,
All chemokines
Induces switch from GDP-bound
inactive form of associated G
protein to GTP-bound active form;
activates cAMP; Ca2+ influx
leading to increased cell motility;
Multiple other effects.
Receptors
without
intrinsic
enzymatic
activity
Many cytokines
including interferons,
growth hormone,
CSFs, EPO
Ligand binding recruits kinases (e.g.,
Janus kinases [JAKs]) that phosphorylate
and activate transcription factors (e.g.,
signal transducers and activators of
transcription [STATs]).

17. 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

18. 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

19. 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.

20. 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

21. • 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;

22. 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.

23. 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

24. 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.

26. • 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

27. 2. Inflammation
• Platelet activation is followed by an influx of
inflammatory cells within the first 1 to 2 days,
led by polymorphonuclear leukocytes (PMN).
• Neutrophils, as well as monocytes, fibroblasts,
and endothelial cells, deposit on a fibrin
scaffold formed by coagulation system.

28. • 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.
• Monocytes come to the wound bed after PMN
and transform into macrophages, which are
abundant during day 2 and 3 but remain there
for weeks.

30. 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,
Granulation tissue formation,
Collagen deposition.
Re-epithelialization.

31. 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

33. 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.

34. • 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

35. • 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.

36. • 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

37. 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)

38. 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.
CONTACT INHIBITION

39. 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

40. 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
3. Granulation tissue formation
4. Collagen synthesis
5. Extracellular matrix formation
REMODELLING 1. Collagen remodeling
2. Vascular maturation and regression

42. 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)

43. 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.

44. • 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

45. • 2nd week; angiogenesis and granulation
significantly decreases, fibroblast proliferation
and collagen synthesis increases.
• 1month; no inflammatory cells, normal
epidermis has forms, but the appendages are
lost permanently. There is cellular connective
tissue

46. 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.

47. • 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

49. Wound strength
• Carefully sutured wounds have approximately
70% of the strength of normal skin
• 10% strength of unwounded skin when sutures
are removed (usually around 1weeks) but rapidly
increases.
• Tensile strength continues to build up for 2
months
• Wound strength reaches approximately 70% to
80% of normal by 3 months and usually does not
improve substantially beyond that point

50. 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

51. 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)

52. 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.

53. 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.

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

57. 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.

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

59. Proud flesh

60. 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

61. contracture

62. 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.

63. Research and Developments in wound
healing
• Wound healing is a complex process, usually
results in satisfactory repair of damaged site.
• However, disruptions caused by tissue loss,
inadequate blood flow and comorbid diseases
may result to chronic wounds -> difficult to treat.
• Many strategies applied to treat wounds in the
past.
• Over the past two decades, advancements in the
clinical understanding of wounds and their
pathophysiology have commanded significant
biomedical innovations in the treatment of
wounds

64. Research and Developments cont…
Latest advancements in wound healing includes;
• Biologics, skin substitutes, biomembranes and
scaffolds
• Stem cells and cellular plasticity
• Scarless wound healing
• Cancer and wound healing

65. Biologics for wound healing
• Biologic wound healing therapies are those that
are intended to facilitate the re-establishment
of the innate repair mechanisms
• May involve the application of active biological
agents, such as plant-derived active
biomolecules which exhibit antioxidant,
antimicrobial, or anti-inflammatory attributes.

66. Biologics for wound healing cont…
• Biologic dressings prevent evaporative water
loss, heat loss, protein and electrolyte loss,
and contamination.
• They also permit autolytic debridement and
develop a granular wound bed.
• Biological skin equivalents, epidermal growth
factors, stem cell therapies, and tissue
engineering might also be utilized.

67. Skin Substitutes
• Skin substitutes are tissue-engineered
products designed to replace, either
temporarily or permanently, the form and
function of the skin.
• Often used in chronic, non-healing ulcers
eg; pressure ulcers, diabetic neuropathic
ulcers and vascular insufficiency ulcers.

68. Skin substitutes cont…
Skin substitutes can be acellular or cellular .
• Acellular products Eg; cadaveric human
dermis with removed cellular components,
contain a scaffold or matrix of hyaluronic acid,
collagen, or fibronectin.
• Cellular products contain living cells such as
keratinocytes and fibroblasts within a matrix.
• These cells can be autologous, allogeneic, or
from another species

69. Goals of skin substitutes
• Provide temporary coverage or permanent
wound closure
• To reduce healing time
• To reduce post-operative contracture
• To improve function
• To decrease morbidity from more invasive
treatments such as skin grafting.

70. Categories of skin substitutes
• Skin substitutes can be divided into three
major categories:
(i) Dermal replacement
(ii) Epidermal replacement
(iii) Dermal/epidermal replacement (full
thickness skin substitutes)

71. Biomembranes
• Biocompatible vegetal biomembranes of
natural rubber/latex, amniotic, polyurethane
and poly-DL-lactic acid (PDLLA) comprise a
class of versatile interventions for the
treatment and healing of wounds.
• Additionally, biomembranes may be
impregnated with a wide range of bioactive
compounds to further facilitate and promote
wound healing.

72. Biomembranes cont…
• Human amniotic membranes ;
• Has been claimed to be one of the most
effective biological skin substitutes used in
burn wounds, with efficiency of
maintaining low bacteria count.
• It also has advantages of reducing loss of
protein, electrolytes and fluids, decreasing
the risk infection, minimising pain,
acceleration of wound healing and good
handling properties..

73. Scaffolds
• Polymeric biomaterials made to provide
structural supportive for cell attachment and
subsequent tissue development
• Acts as ECM substitute for an engineered
tissue.
• Eg ; hydrogels in wounds

74. Stem cells and cellular plasticity
• Stem cells are those cells that have the
capability of self renewal and differentiation.
• Cellular plasticity ability of one cell to adopt
characteristic of another cell
• Eg Mesenchymal stem cells in treatment of
cutaneous wound, embryonic stem cells in
tissue regeneration.

75. • However,the use of embryonic stem cells remains
controversial, as ethical concerns exist regarding
the harvest of cells from live embryos.
• Moreover, the potential for immune rejection
and teratoma formation remains as other
concerns.
• Hence, focus has been redirected towards adult
stem cells as an alternative source with potential
to apply in various disease conditions.

76. Scar-less wound healing
• Skin wounds on early mammalian embryos heal
perfectly with no scars whereas wounds to adult
mammals form scars.
• Thus, embryonic wounds that heal without a scar
have low levels of TGFb1 andTGFb2, low levels of
platelet-derived growth factor and high levels of
TGFb3.
• Different pharmaceutical have been invented to
reduce scar formation based on those
differences,

77. Cancer and wound healing
• Mechanism of healing in normal wounds and
cancerous wound is quite different
• Some mechanism in wound healing provide
way forward in cancer therapeutic
development.
• Also because of the multitude of shared
mechanisms any drug that might improve one
condition might also have unexpected
consequence on the other.

78. References
1.Journal of dental research 89: 219-229, 2010
2. Plastic and Reconstructive Surgery 117: 12s -34s, 2006
3. Cellular aspects of wound healing 84: 257-262, 2009
4. Atlas Oralmaxillofacial Surgery Clinics of North
America 21: 37-47, 2013
5. Advances of stem cell therapetics in cutaneous wound
healing. Mediators of inflammation, 2017-
hindawi.com. E-publication2017, Oct 29.

79. 6. The role of stem cells in wound healing; an
overview. Todays Woundclinic 12: July 2018
7. Hyperbaric oxygen effects on sports injuries.
Therapeutic Advances musculoskeletal Diseases 3:
111-121, 2011.
8. Harsh Mohan Pathology Text Book 6th Edition
9.Robbins textbook of Pathology 9th Edition