wound healing Flashcards
What initiates the process of healing?
Healing is initiated when inflammation begins
What is regeneration in tissue healing?
Replacement of damaged tissue with native tissue, dependent on the regenerative capacity of the tissue.
What are the three types of tissues based on regenerative capacity?
Labile, stable, and permanent tissues.
What are labile tissues?
Tissues with stem cells that continuously cycle to regenerate. Examples:
Small and large bowel (stem cells in mucosal crypts).
Skin (stem cells in basal layer).
Bone marrow (hematopoietic stem cells).
What are stable tissues?
Tissues with quiescent cells (G₀ phase) that can reenter the cell cycle to regenerate when needed. Example: Liver regeneration by compensatory hyperplasia.
What is a classic example of stable tissue regeneration?
Liver regeneration after partial resection, where hepatocytes produce additional cells and then reenter quiescence.
Which tissues lack significant regenerative potential?
Permanent tissues like myocardium, skeletal muscle, and neurons.
What is the process of repair in tissue healing?
Replacement of damaged tissue with a fibrous scar.
When does repair occur?
When regenerative stem cells are lost (e.g., deep skin cut) or the tissue lacks regenerative capacity (e.g., myocardial infarction)
What are the components of granulation tissue in the initial repair phase?
Fibroblasts: Deposit type III collagen.
Capillaries: Provide nutrients.
Myofibroblasts: Contract the wound.
What happens during scar formation?
Type III collagen in granulation tissue is replaced with type I collagen
What are the properties of type III and type I collagen?
Type III: Pliable, found in granulation tissue, embryonic tissue, uterus, and keloids.
Type I: High tensile strength, found in skin, bone, tendons, and most organs.
What is required for replacing type III collagen with type I collagen?
Collagenase, with zinc as a cofactor
What mediates tissue regeneration and repair?
Paracrine signaling via growth factors (e.g., macrophages targeting fibroblasts).
Examples of growth factors in tissue repair include?
TGF-α: Epithelial and fibroblast growth.
TGF-β: Fibroblast growth, inflammation inhibition.
PDGF: Endothelium, smooth muscle, and fibroblast growth.
FGF: Angiogenesis, skeletal development.
VEGF: Angiogenesis.
What is primary intention in cutaneous healing?
Wound edges are brought together (e.g., suturing), leading to minimal scar formation.
What is secondary intention in cutaneous healing?
Edges are not approximated, granulation tissue fills the defect, and myofibroblasts contract the wound to form a scar.
What are common causes of delayed wound healing?
Infection (e.g., Staphylococcus aureus).
Deficiency in vitamin C, copper, or zinc.
Presence of a foreign body, ischemia, diabetes, or malnutrition.
Why is vitamin C important in wound healing?
It is a cofactor for hydroxylation of proline and lysine residues in procollagen, which is necessary for collagen cross-linking.
What role does copper play in collagen stabilization?
Copper is a cofactor for lysyl oxidase, which cross-links lysine and hydroxylysine to form stable collagen.
Why is zinc essential in collagen remodeling?
Zinc is a cofactor for collagenase, which replaces type III collagen in granulation tissue with stronger type I collagen.
What are common causes of delayed wound healing besides nutrient deficiencies?
Foreign body, ischemia, diabetes, and malnutrition.
What is dehiscence, and where is it most commonly observed?
Dehiscence is the rupture of a wound, most commonly seen after abdominal surgery.
What characterizes a hypertrophic scar?
Excess production of scar tissue localized to the wound.
What is a keloid?
Excess production of scar tissue out of proportion to the wound.
Characterized by excess type III collagen.
More common in African Americans and often affects earlobes, face, and upper extremities.
