Pathophysiology - Tissue Repair and Wound Healing

Tissue Repair and Wound Healing

• Regeneration
• Replacement of injured tissue of the same parenchymal type
• Leaves little or no evidence of injury
• Labile cells
• Continue to divide ad replicate throughout life, found in tissues with daily turnover of cells
• Surface of epithelial cells of the skin, oral cavity, vagina, cervix
• Stable cells
• Normally stops dividing when growth ceases (liver cells)
• Capable of regeneration when supporting stromal framework is present
• Permanent or fixed cells
• Cannot undergo mitotic division
• Nerves, skeletal cells, cardiac muscle cells
• Connective tissue repair
• Allows replacement of nonregenerated parenchymal cells by a connective scar tissue
• 4 Phases
• Inflammatory phase
• Hemostasis
• Activated immediately at the time of injury
• Constriction of injured blood vessel and initiation of blood clotting by platelet activation and aggregation
• Same vessels dilate and capillaries increase their permeability, allowing plasma and blood components to leak into the injured are, becomes hard
• Cellular phase
• Migration of phagocytic white blood cells that digest and remove invading organisms, extracellular debris and foreign materials
• Essential cells in the healing process
• Neutrophils or polymorphonuclear cells – day 3-4
• Macrophage – 24 hours after polymorphonuclear cells
• Proliferative phase
• 2-3 days of injury to 3 weeks
• Fibroblasts
• Connective tissues that synthesize and secrete collagen and other elements needed for wound healing
• Builds tissue to fill wound spaces
• Pink granular tissue (granulation tissue)
• Fragile, bleeds easily
• Epithelial cells - begin to regenerate moving towards the center of the wound
• Remodelling phase
• 3 weeks to 6 months or longer
• Continued remodelling, increase tension strength (80% regained)
• Keloid formation
• Tumor-like masses caused by excess production of scar tissue, genetic basis.

Factors that affect wound healing

1. Malnutrition - adequate store of protein, carbohydrate, fat, vitamins and minerals
• Protein deficiency
• Prolongs healing process, impairs fibroblast proliferation, collagen protein matrix synthesis and wound remodelling
• Carbohydrates – energy source for white blood cells
• Fats – essential constituents of cell membrane needed for synthesis of new cells
• Vitamin C – needed for collagen synthesis, speeds healing process
• Vitamin A – stimulates and supports epithelialization, capillary formation and collagen synthesis
• Vitamin K – prevents bleeding
2. Blood flow and oxygen delivery
3. Impaired inflammatory and immune response
• Phagocytic function
• Extrinsic – impairs attraction of phagocytic cells to wound site
• Intrinsic – enzymatic deficiencies in metabolic pathway for destroying ingested bacteria by phagocytic cells
4. Diabetes mellitus – effects of hyperglycemia on phagocytic function
5. Corticosteroids
• Decreases inflammatory process, delays healing
• Decreases capillary permeability, impairs phagocytic activity of leukocytes, ibhibits fibroblast proliferation and function
6. Infection, wound separation, foreign bodies
• Delays healing process
• Infection – prolongs inglammatory phase, impairs formation of granular tissues, inhibits proliferation of fibroblasts and deposition of collagen fibers
7. Effects of age
• Rate of cell replacement shows with aging