Lecture # 32 TISSUE REPAIR: REGNERATION, HEALING & FIBROSIS - 4 Dr Lecture # 32 TISSUE REPAIR: REGNERATION, HEALING & FIBROSIS - 4 Dr. Iram Sohail Assistant Professor Pathology College Of Medicine Majmaah University

OBJECTIVES Explain the mechanism of cutaneous wound healing Discuss healing by first intension Discuss healing by second intention Discuss wound strength Explain the pathological aspects & overview of repair process

Cutaneous wound healing (Healing of skin wound) This process involves the epithelial regeneration & formation of connective scar. This re-epithelialization occurs mostly by migration of cells from edges of wound.

The growth factors involved are

Cutaneous wound healing has 3 phases Inflammation Formation of granulation tissue ECM deposition & remodeling

Healing of cutaneous wound occurs by Healing by first intention Or Healing by second intention

Healing by first intention It is the healing of a clean, uninfected, surgical incision approximated by surgical sutures. A small scar is formed with minimum wound contraction.

Sequence of events Within 24 hours 24 to 48 hours Fibrin clot is formed Neutrophils 24 to 48 hours The epithelial cells from both edges begin to migrate and meet in midline & a thin continuous epithelial layer is formed.

Day 3 Neutrophils are replaced by macrophages Starting of granulation tissue formation Collagen fibers appear Thick epithelial layer is formed

Day 5 Neovascularization & granulation tissue formation completed More collagen fibers Epidermis recovers its normal thickness Surface keratinization

2nd week First month Increased fibroblast & collagen deposition Vascular channels regress First month A scar is formed, composed of connective tissue No inflammatory cells Covered by normal epidermis Dermal appendages (sweat gland, hair follicles) are destroyed permanently

Healing by second intention When tissue loss is more extensive, such as in large wounds, ulceration, abscess formation, the repair process is more complex and called healing by second intension.

Inflammatory reaction is more intense with more granulation tissue along with wound contraction. Accumulation of ECM and large scar formation. Larger clot formation, rich in fibrin Much larger granulation tissue is formed Great scar formation Wound contraction (myofibroblasts)

Wound strength A carefully sutured wound has 70% strength of normal (unwounded) skin. Wound strength is caused by increased collagen synthesis. The strength of wound progresses rapidly and reaches at 70—80% at 3 month, but does not improve beyond this.

Pathological aspects of wound healing Following factors can alter the quality of wound healing Infection Delays wound healing

Protein deficiency Vitamin . C - deficiency Delays wound healing Delays wound healing (because of decrease collagen synthesis)

Glucocorticoid (Steroid) administration Delays wound healing (because steroids cause decrease fibrosis) Local pressure or torsion Poor wound healing Poor perfusion of blood Delays wound healing

Diabetes mellitus Foreign body Poor wound healing (Such as glass, steel) delays wound healing

Keloid Accumulation of very big amount of collagen in wound can result in a prominent, raised, ugly looking scar, known as keloid. More common in blacks It is mostly heritable (transfer from parents to children)

Overview of repair process