Wound Healing

Wound healing is where there's acute inflammation due to infection/tissue damage. Dead cells are removed, healing starts with organisation (formation of granulation tissue), and ends with complete resolution (back to normal) or just repair (scar).

Primary intention - This occurs when there's injury to the epithelial layer only, so complete regeneration can occur, e.g. clean wound, small incision

Secondary intention - This occurs when there's lots more tissue damage/loss, so it's repaired by regeneration and fibrosis e.g. large wounds, abscesses, ulcer, ischaemic necrosis

Stages of Primary Healing

1. Injury/wound activates coagulation, which leads to the formation of clots

2. Neutrophils surround the margins of the wound and release proteolytic enzymes to remove the debris/microbes

3. Epithelial cells migrate and proliferate at the wound’s edges and meet in the midline to close the wound

4. Macrophages replace the neutrophils, and granulation tissue starts to invade and fill the wound space - Neovessels and oedema forms

5. Proliferation of fibroblasts produces collagen, which deposits in the wound, and new vessels begin to be removed, and inflammation decreases

Secondary Healing

This differs from Primary Healing as there's:

• A bigger clot, more oedema, and more intense inflammation

• More granulation tissue so a bigger scar will form

• Wound contraction due to the size of the wound

• Myofibroblasts used, which are modified fibroblasts with smooth muscle features

Factors that affect healing

• Age – Skin gets thinner, and the body shows a decreased inflammatory response so, as you get older, your skin is predisposed to injury and will heal slower

• Nutrition – Proper nutrition is vital to optimal healing, as a wound needs the necessary nutrients for cell repair and growth

• Obesity

• Chronic conditions – CVD, DM and Immunodeficiency can slow down wound repair

• Medication – NSAIDS, Anticoagulants, Immunosuppressants