CUTANEOUS WOUND HEALING

BYFIRST AND SECOND

INTENTIONBy:

Dr. Kinz

CUTANEOUS WOUND HEALING

STAGES OF NORMAL CUTANEOUS

WOUND HEALING

CLASSIFICATION OF WOUND

HEALING

A. Primary Union (First Intention)

• Clean uninfected surgical incision approximated by

sutures.

• Death of limited number of epithelial and connective

tissue.

• Basement membrane damage is minimal.

• Relatively thin scar formation.

B. Secondary Union (Second Intention)

• Larger defects, the edges are not attached properly,

formation of granular tissue.

• Extensive loss of cells and tissues with intense

inflammatory reaction and collagen formation.

• Fibrin clot is larger, there is more exudate and necrotic

debris.

• Granular tissue substantial scar formation which

contracts.

• Involves wound contraction.

FORMATION OF BLOOD CLOT

• Activation of coagulation pathways leading to clot

formation which prevents bleeding

• Release of Vascular Endothelial Growth Factor(VEGF)

with increased permeablity and edema

• Dehydration at the external surface of clot makes a scab

that covers the wound.

• Larger fibrin clot is seen in healing by second intention

with more exudate and necrotic debris in the wound.

• Within 24 hours, neutrophils appear at the margins of

the incision.

FORMATION OF

GRANULATION TISSUE

• Hallmark of repair.

• Occurs in the first 24 to 72 hours due to fibroblast and

vascular endothelial cell proliferation.

• Soft, pink and granular appearance on the surface of

wounds.

• The newly formed blood vessels are leaky leading to

passage of plasma proteins and fluid into extravascular

space – edematous in appearance.

• By 5 to 7 days the granulation tissue fills up the wound area

(more pronounced effect in healing by second intension).

CELL PROLIFERATION AND

COLLAGEN DEPOSITION

• Neutrophils are replaced by macrophages by 48 to 96 hours

which play role in clearing extracellular debris, fibrin and

other foreign material, promoting angiogenesis and

extracellular matrix deposition

• Fibroblast migration by chemokines and their subsequent

proliferation

• Deposition of collagen at the margins of the incision –

vertically oriented in primary intention and horizontally

oriented in secondary intention

• In 24 to 48 hours proliferation and migration of epithelial

cells adjacent to wound, migration to the margins of dermis,

depositing basement membrane components.

• Epithelial cell proliferation thickens.

• collagen fibrils (type I collagen) become more abundant and

bridges the incision.

EPITHELIZATION

SCAR FORMATION

• By second week, there is increased accumulation of

collagen with regression of vasculature.

• The granulation tissue is converted into pale, avascular scar

composed of spindle shaped fibroblasts, dense collagen,

also there is elastic tissue, and other extracellular matrix

components.

WOUND CONTRACTION

• Primarily occurs in healing by secondary intention.

• Formation of myofibroblasts from the tissue fibroblasts.

• These cells contract in the wound and produce large amount

of extracellular martrix components.

CONNECTIVE TISSUE

REMODELING

• The balance between extracellular matrix synthesis and

degradation results in remodeling of connective tissue

framework

• Matrix metalloproteinases e.g. interstitial collagenases,

gelatinases degrade the ECM, and are inhibited by Tissue

Inhibitors of metalloproteinases .

RECOVERY OF TENSILE

STRENGTH

• Tensile strength in healing wound is provided my fibrillar

collagens (type I collagen) with cross linking and increased

fibre size.

• Sutures are removed typically at first week, the wound

strength is 10% of normal.

• By 3rd month the strength plateaus upto 70 to 80% of

normal.