Wound Healing and Repair

Key points

• • Healing happens in two ways: regeneration replaces lost cells with the same type, while repair fills the defect with fibrous scar tissue when regeneration is not possible.
• • Whether a tissue can regenerate depends on its cells: labile cells (skin, gut lining) and stable cells (liver, normally quiescent) can divide, whereas permanent cells such as heart muscle and central nervous system neurons essentially cannot and heal by scar.
• • Healing by first intention is the neat closure of a clean surgical cut with little tissue loss, which gives a thin scar.
• • Healing by second intention is the slower filling of a large open wound from its base by granulation tissue, with a bigger scar and wound contraction.
• • Granulation tissue is new connective tissue with tiny new blood vessels and fibroblasts; it lays down collagen that is later remodelled and strengthened.
• • Healing is delayed by infection, a poor blood supply, diabetes, old age and a poor protein or vitamin C intake, and it can be complicated by an excessive keloid scar.