RepairRepair

* Definition: Replacement of damaged tissue

with new healthy living tissue.

* 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 .

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.

* 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

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.

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. .

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.

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.

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.

• 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.

Granulation tissueGranulation tissue

Granulation tissueGranulation tissue

capillary

fibroblast

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).

* 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.

* 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.

* 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 .

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.

• 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.

Hypertrophic scar Keloid

Keloid

A B

* 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.

II. General factors:

•Age of patient.

•Nutrition status.

•Diseases: Diabetes, malignancy, anaemia.

•Drugs: Corticosteroid therapy, chemotherapy..

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