Repair. * Definition: Replacement of damaged tissue with new healthy living tissue.
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Transcript of Repair. * Definition: Replacement of damaged tissue with new healthy living tissue.
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RepairRepair
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* Definition: Replacement of damaged tissue
with new healthy living tissue.
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* Types of the cells according to the power of * Types of the cells according to the power of cell division:cell division:
1. Labile cells: 1. Labile cells: are contentiously dividing cells and
renew themselves: e.g. skin epithelium, mucosal lining
of the GIT, haematopoietic cells (blood cells ).
2. Quiescent cells (Stable): 2. Quiescent cells (Stable): cells divide when there is
a need e.g. liver, kidney and pancreas .
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3. Permanent cells: 3. Permanent cells: Non-dividing cells so when
injured heal by fibrous tissue or glial tissue (in CNS only)
e.g. nerve cells and skeletal, cardiac muscle cells.
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* Types of repair:A. Regeneration:A. Regeneration:
•Replacement of the damaged cells by new healthy cells
of the same type.
•Done by proliferation of the adjacent healthy cells.
•Occurs with minor damage of labile cells and stable
cells.
•Examples: mild liver injuries and bone fractures
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B. Fibrosis or gliosis: B. Fibrosis or gliosis:
•Replacement of the damaged tissue by fibrous tissue or
glial tissue (in CNS).
•Occurs in the healing process of permanent cells or in
stable cells with marked damage.
•Examples:
1. Myocardial infraction: heal by fibrosis.
2. Cerebral infarction. Heal by gliosis.
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Wound HealingWound Healing• Cutaneous wound healing is generally divided into 4
phases:
1.1. Hemostasis.Hemostasis.
2.2. Inflammation. Inflammation.
3.3. Granulation tissue formation and Re-Granulation tissue formation and Re-
epithelializationepithelialization
4.4. Fibrous tissue formation and remodelingFibrous tissue formation and remodeling. .
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1. Homeostasis1. Homeostasis• Immediately after injury the cut vessels bleed inside the wound
defect to form a blood clot that unit the two cut ends temporarily.
• Vasoconstriction of the injured vessels at the edges of the wound
followed by platelets aggregation and adherence to the damaged
endothelium.
• Stimulation of coagulation system will form fibrin.
• Fibrin network is formed over the aggregated platelets to form a
homeostatic plug that stops bleeding inside the wound.
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2. Inflammation2. Inflammation • Mediated by polymorphs and macrophages.
• Within the first 6-8 hours, the polymorphonuclear
leukocytes (PMNs) kill any organism in the wound and
liquefy any necrotic debris.
• As the process continues, monocytes also exude from
the blood vessels. These are termed macrophages. The
macrophages continue and engulf the necrotic debris.
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3. Granulation tissue formation and re-3. Granulation tissue formation and re-epithelizationepithelization
• In days 5-7, fibroblasts migrate into the wound.
• Angiogenesis is the formation of new capillaries
from the healthy blood vessels at the edge of
the wound. These new capillaries fill the wound
defect and surrounded by fibroblasts.
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• The newly formed capillaries + fibroblasts =
granulation tissue.
• Re-epithelization occurs by proliferation and
migration of the healthy epidermal cells from
the edges of the wound inwards.
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Granulation tissueGranulation tissue
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Granulation tissueGranulation tissue
capillary
fibroblast
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4. Fibrous tissue formation and 4. Fibrous tissue formation and remodeling remodeling
• After the third week, fibroblasts lay down
collagen fibers types I and III.
• Excess collagen is degraded by collagenase
enzyme which secreted from macrophages in a
controlled manner (remodelling).
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* Wound contraction: * Wound contraction:
• Is a process done by myofibroblasts (modified
fibrobalsts), which resemble contractile
smooth muscle cells.
• This occurs to give the healing wound more
strength.
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* Types of wound healing:* Types of wound healing:1. Healing by primary union:-Occurs with clean, non-gaping wounds (stitched surgical incision).-The result scar is small, thin, regular and flat.2. Healing by secondary union: - Occurs with extensive tissue loss as in: large wounds, infected wounds, abscess, ulcers….etc.- The resulting scar is large, thick, irregular and elevated.
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* Complications of wound healing:* Complications of wound healing:
1. Ulcers: 1. Ulcers: discontinuity of the covering epithelium
or mucous membrane .
2. Sinus: 2. Sinus: is blind end track of septic granulation
tissue connecting a cavity to the outside e.g.
pilonidal sinus
3. Fistula: 3. Fistula: is a tract of septic granulation tissue
connecting 2 epithelial surfaces e.g. perianal fistula.
4. Weak atrophic scar: 4. Weak atrophic scar: this may lead to hernia .
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5. Hypertrophied scar. 5. Hypertrophied scar.
•Large sized scar that don’t grow beyond the
boundaries of the original wound.
6. Keloid formation: 6. Keloid formation:
•Large sized scar that grow beyond the boundaries
of the original wound and even infiltrating the
surrounding tissue.
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• Its periphery shows claw-like extensions.
• Occurs due to overproduction of collagen or
defect in its degradation.
• Affect certain genetically predisposed
persons.
• Radiotherapy is curative.
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Hypertrophic scar Keloid
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Keloid
A B
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* Factors affecting Repair:* Factors affecting Repair: I. Local factors :•The type of the damaged cells (labile, stable or permanent).•Severity of the damage.•Presence of foreign body.•Presence of necrotic tissue.•Infection.•Irradiation.•Blood supply.
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II. General factors:
•Age of patient.
•Nutrition status.
•Diseases: Diabetes, malignancy, anaemia.
•Drugs: Corticosteroid therapy, chemotherapy..
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