Wound healing can be accomplished in one of the following two ways:
→ Healing by first intention (primary union)
→ Healing by second intention (secondary union).
HEALING BY FIRST INTENTION (PRIMARY UNION)
This healing occurs when a wound has the following characteristics:
- clean and uninfected.
- surgically incised
- not much loss of cells and tissue
- edges of wound are approximated (closed) by surgical sutures.
Sequence of events-
1. Initial haemorrhage- Immediately after iinjury,blood clotting takes place
2. Acute inflammatory rresponse—occurs within 24 hours.
3. Epithelial changes-→ The epidermis of sthe skinfrom both the cut margins starts proliferating.
→Wound is covered by a layer of epithelium in 48 hours.
→The migrated epidermal cells separate the underlying
→By 5th day, a multi-layered new epidermis and new collagen fibrils start forming which dominate till healing is completed.
→In 4 weeks, the scar tissue is formed.
HEALING BY SECOND INTENTION (SECONDARY UNION)
This healing occurs when a wound has the following characteristics:
i) open with a large tissue defect, at times infected.
ii) having extensive loss of cells and tissues; and
iii) the wound is not approximated by surgical sutures but is left open.
Events-
Initial events of haemorrhage, inflammation and epithelial changes are similar to primary union.
During formation of epithelial layer, granulation tissue will be developed. New blood vessels and cells will develop.
COMPLICATIONS OF WOUND HEALING
Healing by second intention is slow.
Healing by second intention leaves large, at times ugly, scar as compared to a neat scar of primary union.
The wound may get infected due to entry of bacteria delays the healing.
REFERENCES:
Harsh Mohan; Text book of Pathology; 6 th edition; India; Jaypee Publications; 2010
