Healing occurs through regeneration or repair and involves granulation tissue formation. Regeneration fully replaces damaged tissue, while repair uses scar tissue. Granulation tissue forms within 1-3 days from new blood vessels and fibroblasts, filling wounds within a week. Primary wound healing occurs with minimal tissue loss and a thin scar. Secondary healing involves more tissue loss and granulation, with a substantial scar and possible wound contraction. Factors like infection, foreign bodies, wound size/location, and nutrition influence healing. Complications include deficient or excessive scarring that cause issues like dehiscence, hernias, hypertrophic scarring, and contractures.

1. WOUND HEALING
INTRODUCTION
Healing is defined as process of replacement of dead tissue by living tissue. Healing may be by
regeneration or by repair.
 Regeneration: Regeneration is a process in which lost/damaged tissue is completely
replaced by tissue of similar type.
Regeneration occurs in tissues consisting of cells with regenerative activity. These
include hematopoietic cells, epithelium of the skin and gastrointestinal (GI) tract.
 Repair: Repair is defined as a process in which lost/damaged tissue is replaced by fibrous
tissue or scar, e.g. healed myocardial infarction. The term healing and repair is commonly
used synonymously.
Factors Deciding the Pattern of Healing
Mostly healing occurs by a combination of both regeneration and repair. The proportion of
regeneration and repair in healing process depends on the regenerative capacity of the
lost/damaged tissue. According to regenerative capacity of the cells, the tissues of the body can
be divided into three groups.
 Continuously dividing (labile) tissues: They proliferate throughout life. For examples,
stratified squamous epithelium of the skin, oral cavity, vagina and cervix; columnar
epithelium of the GI tract and uterus.
 Quiescent (stable) tissues: They normally do not proliferate. However, they can rapidly
proliferate in response to stimuli or demand. For examples, parenchymal cells (of liver)
and mesenchymal cells (e.g. fibroblasts).
 Nondividing (permanent) tissues: These consist of cells which cannot divide after birth,
e.g. neurons, skeletal muscle cells and cardiac muscle cells.
Granulation Tissue
 During the first 24-72 hours of the healing process, the proliferation of fibroblasts and
vascular endothelial cells begins. It forms a specialized type of tissue known as
granulation tissue, which is characteristic of tissue repair.

2.  The term granulation tissue is derived from its pink, soft, granular gross appearance on
the surface of healing wounds. Microscopically, it consists of new small blood vessels
(angiogenesis) and proliferation of fibroblasts. The blood vessels are leaky, and are
responsible for edema seen in granulation tissue.
 Granulation tissue progressively grows into the incision space/wound. The amount of
granulation tissue is more prominent in healing by secondary union. It depends on the
size of the tissue deficit created by the wound and intensity of inflammation.
 The granulation tissue fills the wound area by about 5-7 days.
CUTANEOUS WOUND HEALING
Healing by Primary Union or by First Intention
Healing of a clean, uninfected surgical incision in the skin approximated by surgical sutures is
known as healing by primary union or by first intention. Surgical incision causes death of a
minimum number of epithelial and connective tissue cells. The disruption of epithelial basement
membrane continuity is also minimal. Re-epithelialization occurs with a relatively thin scar. This
is simplest type of cutaneous wound healing. Various stages in the healing by first intention are:
 First 24 hours: Blood clots in the space between sutured margins. Neutrophils appear at
the margins of incision. Epithelial cells at the edges undergo proliferation and migration
across the wound.
 Day 2: Macrophages begin to appear. Surface epithelial continuity is re-established in the
form of a thin surface layer.
 Day 3-7: Granulation tissue begins to invade tissue spaces. Surface epithelial achieves
normal thickness. Collagen is progressively laid down. Acute inflammatory response
begins to subside.
 Day 10-14: Wound normally gains about 10% strength of normal skin. Further fibroblast
proliferation occurs with collagen deposition.
 Weeks to months: Collagen deposition along the line of stress and wound gradually
achieves maximal 80% of tensile strength of normal skin.

3. Healing by Secondary Union or by Second Intention
When injury produces large defects on the skin surface with extensive loss of cells and tissue, the
healing process is known as healing by secondary union or by second intention. Healing in such
cutaneous wound is more complicated. Basic mechanisms of healing by primary (first intention)
and secondary (second intention) union are same. The features of healing by secondary intention
are:
- The inflammatory reaction is severe.
- There is formation of abundant granulation tissue.
- It also shows extensive deposition of collagen with substantial scar formation, which may
contract.
- Presence of wound contraction.
Wound Contraction
Wound contraction generally occurs in large surface wounds and is an important feature in
healing by secondary union.
Advantages of the wound contraction: It decreases the gap between dermal edges of the wound
and reduces the wound surface area. Myofibroblasts of granulation tissue have ultra structural
features of smooth muscle cells. They contract in the wound tissue and are responsible for wound
contraction.

4. Figure- Healing by primary and secondary intention
FACTORS THAT INFLUENCE WOUND HEALING
Local Factors
 Infection: It is the most important local cause for delay in healing.
 Mechanical factors: Movement of wounded area can result in delayed healing.

5.  Foreign bodies: Unnecessary sutures or fragments of steel, glass, or bone can delay
healing.
 Size and type of wound: Small wounds due to surgical incision or other injuries heal
quickly with less scar formation than large wounds.
 Location: Wound healing is delayed at sites in which skin covers bone with little
intervening tissue where skin cannot contract (e.g. skin over the anterior tibia).
 Blood supply: Wounds in areas with good blood supply, such as the face, heal faster than
those with poor blood supply, such as the foot. For example, varicose veins of the legs
decrease the venous drainage and can cause non healing of ulcers.
 Ionizing radiation: It decreases healing process.
 Complications of wound healing: They may delay wound healing.
Systemic Factors
 Nutrition: Protein deficiency, vitamin C deficiency, inhibits collagen synthesis and
diminishes healing process.
 Age: Wound healing is rapid in young compared to in aged individuals.
 Metabolic status: Diabetes mellitus is associated with delayed healing.
 Circulatory status: Inadequate blood supply (e.g. arteriosclerosis) or venous
abnormalities (e.g. varicose veins) that retard venous drainage delay healing.
 Hematological abnormalities: Defects in neutrophils and bleeding disorders may slow
the healing process.
COMPLICATIONS OF WOUND HEALING
Complications can be grouped into three general categories:
 Deficient scar formation:
- Inadequate formation of granulation tissue or a deficient scar formation can
cause wound dehiscence (wound splitting open).
- Incisional hernia resulting from weak scars of the abdominal wall due to a defect
caused by prior surgery.
 Excessive formation of the repair components: It can result in:
- Hypertrophic scar
- Keloid

6. - Exuberant granulation tissue: Pyogenic granuloma or granuloma pyogenicum
which consists of the localized, formation of excessive amounts of granulation
tissue (proud flesh).
- Excessive contraction: A decrease in the size of a wound is known as wound
contraction. An exaggeration of this contraction is termed contracture.