HEALING_AND_REPAIR_-_MBchB_2.1p king Caesar University

Healing and repair

1. Tissue repair/
wound healing
By Dr. WaiswaAli
Department of Pathology

2. Definitions
Repair: replacement of the lost tissues
following an insult , it can be in form of regeneration or
healing.
Repair processes are critical for the maintenance of
normal structure and function and survival of the
organism.

3. The healing of skin wounds and various other conditions
such as regeneration of hepatocytes and epithelial cells
are just the most common examples of repair processes.
Repair, in the form of regeneration or healing, occurs
after practically any insult that causes tissue
destruction.

4. Regeneration
Regeneration:refers to growth of cells and tissues to
replace lost structures, such as replacement of surface epithelial tissue
following insult or injury.

5. Tissues with high proliferative capacity, such as the hematopoietic system
and the epithelia of the skin and gastrointestinal tract, renew themselves
continuously and can regenerate after injury, as long as the stem cells of
these tissues are not destroyed.
Regeneration requires an intact connective tissue scaffold.

6. Healing
Healingis usually a tissue response :
(1) to a wound (commonly in the skin),
(2) to inflammatory processes in internal organs, or
(3) to cell necrosis in organs incapable of regeneration.
Healing consists of variable proportions of two distinct
processes;

7. Regeneration, and the laying down of fibrous tissue, or
scar formation.
Superficial wounds, such as a cutaneous wound that
only damages the epithelium, can heal by epithelial
regeneration.

8. Steps of repair/healing
Induction of an inflammatory process in response to
the initial injury, with removal of damaged and dead
tissue.
Also, during this phase, injury to the tissue that result
in blood flow initiates the clotting cascade
Proliferation and migration of parenchymal and
connective tissue cells.


9. Formation of new blood vessels (angiogenesis) and
granulation tissue.
Synthesis of Extra Cellular Matrix proteins and
collagen deposition
Extracellular matrix protein (collagen, fibrin,
fibronectin) give support, make the cellular structure
and help in communication among cells

10. In 5-7 days fibroblasts that have migrated to the site of injury lay new
collagen (initially type III that is later replaced by type I)

11. Wound contraction.
This is a healing process that works to reduce the size of
the tissue defect and subsequently decrease the amount
of damaged tissue that needs repair
The process requires myofibroblast cells that are found
in the margins of the healing wound.

12. Acquisition of wound strength
The gain of tensil strength of wounds occurs over time
with maximun strength attained after about 4-6 weeks
especially for the post operative wounds
However, most wounds reach their peak tensil strength
by the 8
th
week. This may be affected by size of wound,
location and other factors that affect wound healing.

13. Tissue remodeling.
This involves re-organisation and restoration of the existing tissues
The wound water content reduces, the collagen laid down during
proliferation is gradually replaced by more stable interwoven collagen
For Bone, tissue remodeling is carried out by osteoclasts


14. Factors Influencing Wound
Healing
LOCAL
Infection/inflammation
Foreignbodies
Inadequatecirculation
Movement
Extentofdamage
Irradiation
Corticosteroids
Size,location,andtype
ofwound
SYSTEMIC
Age
Nutritionalstatus:
-proteindeficiency
-vitaminCdeficiency
-zincdeficiency
Chronic disease
conditions like Diabetes
mellitus, cancers

15. Outcome of wound healing
RESOLUTION: tissue completely restored to normal
structure and function
REGENERATION:proliferation of remaining cells
with some loss of normal
structure
ORGANISATION:replacement of lost tissue with
granulation tissue and fibrous repair

16. Cutaneous wound healing
Two types of healing:
Healing by first intention/primary intension
Clean, incised wound
If edges are held together
Healing by secondary intention
Separated edges
More severe damage and lost of
tissue.
More intense inflammation.
Slower, leaves a larger scar

17. Healing by First Intention/
primary intension
This refers to healing of a wound in which edges are
closely re-approximated
There is minimal granulation tissue and scar formation
Blood clot –immediate
Acute inflammation is at site of injury by 6-12 hrs
Epithelial cells proliferate from basal layers
Macrophages migrate to site of injury within–24 hrs
Minimal granulation tissue is seen in about 3 days

18. Healing by First
Intention/primary intension
Collagen deposition, decreased vascularity , decreased
inflammation–1-2 weeks
Contraction –complete by 6 weeks

19. Healing by First
Intention/primary intension
If a wound due to trauma is clean and the edges are
sharp, it should be closed within less than 6 hours to
enable healing by primary intension.
Earlier closing of the clean wound prevents colonization
by bacteria and also minimizes scar formation.
If the edges are not approximated the wound will heal
by secondary intension

20. Healing by Secondary
Intention
This occurs when the edges of the wound are not
apposed or approximated.
The wound healing takes place naturally to fill the
defect
It is characterised by visible granulation tissue and the
scar formed will be bigger than that from wounds
healing by primary intension.
This is seen in cases where there is extensive tissue loss
with need for considerable tissue regeneration like in
fourth degree burns
Can also be seen when a wound is considered dirty

21. Healing by Secondary
Intention
Wound is filled with clot –immediate
Contraction of edges occurs and acute inflammation
occur within –6-12 hrs
macrophages migrate to –24 hrs
Epithelial cells grow in from edges
Much more granulation starts to grow as it replaces the
clot from 3 days on words
However this duration may be longer is the wound
defect is large.

22. Epithelium grows over hair follicles and sweat glands
that were completely destroyed are NOT replaced
Contraction –6-8 weeks

23. Complications of Wound
Healing
Infection.
Delay healing with continued tissue damage
Overgrowth.
‘proud flesh’ preventing epithelialisation
Keloid
Excess collagen production
Contractures.
These can cause;
Skin deformity
Obstruction of hollow viscus eg oesophagus
Stenosis due to scarred heart valves

24. Complications of Wound
Healing
Neuroma
Proliferation of nerve fibres
pain
Herniation
weaker tensile strength of scar
eg incisional hernia, cardiac aneurysm
Burst abdomen.
Cancer
Chronic scarred ulcer –eg Marjolin’s Ulcer (Squamous cell
carcinoma)

25. keloid

26. Healing in special tissues
Liver
Followed by complete regeneration, formation of scars
or both
Hepatocytes lost after focal necrosis are restored by
regeneration, normal architecture restored
In massive hepatic necrosis, there is regeneration with
formation of irregular nodules separated by scars
Forms of chronic hepatic injury that destroy the
extracellular matrix (eg alcoholic liver injury) elicit a
combination of regeneration and fibrosis, an
appearance termed cirrhosis

27. Healing in special tissues
Bone(Fracture)-Assignment to read.

28. THANK YOU