Inflammation (days 1–10) – PMNs, macrophages; epithelialization (1–2 mm/day)
Proliferation (5 days–3 weeks) – fibroblasts, collagen deposition, neovascularization, granulation tissue formation; type III collagen replaced with type I
Remodeling (3 weeks–1 year) – decreased vascularity
• Net amount of collagen does not change with remodeling, although significant production and degradation occur
• Collagen cross-linking occurs
Peripheral nerves regenerate at 1 mm/day
Order of cell arrival in wound
• Platelets
• PMNs
• Macrophages
• Lymphocytes (recent research shows arrival before fibroblasts)
• Fibroblasts
![](https://i0.wp.com/basicmedicalkey.com/wp-content/uploads/2017/06/image00509.gif?w=960)
Macrophages are essential for wound healing (release of growth factors, cytokines, etc.)
Fibronectin – chemotactic for macrophages; anchors fibroblasts
Fibroblasts – replace fibronectin-fibrin with collagen
Predominant cell type by day
• Days 0–2 – PMNs
• Days 3–4 – macrophages
• Days 5 and on – fibroblasts
Platelet plug – platelets and fibrin
Provisional matrix – platelets, fibrin, and fibronectin
Accelerated wound healing – reopening a wound results in quicker healing the 2nd time (as healing cells are already present there)
Epithelial integrity – most important factor in healing open wounds (secondary intention)
• Migration from hair follicles (#1 site), wound edges, and sweat glands
• Dependent on granulation tissue in wound
• Unepithelialized wounds leak serum and protein, promote bacteria
Tensile strength – most important factor in healing closed incisions (primary intention)
• Depends on collagen deposition and cross-linking of collagen
Submucosa – strength layer of bowel
• Weakest time point for small bowel anastomosis – 3–5 days
Myofibroblasts (smooth muscle cell–fibroblast; communicate by gap junctions)
• Involved in wound contraction and healing by secondary intention
• Perineum has better wound contraction than leg
![](https://i0.wp.com/basicmedicalkey.com/wp-content/uploads/2017/06/image00510.gif?w=960)
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