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4 Cards in this Set
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- Back
- 3rd side (hint)
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Compare and contrast repair, regeneration and healing.
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Repair: the process of returning to the original anatomical structure.
Regeneration: implies that repair has allowed for most if not all of all of the original anatomical architecture to be replaced by the growth of new cells and tissues Healing: implies that the repair process has not allowed for full restoration of the anatomical architecture. there may have been scar tissue (fibrosis due to collagen deposit) formed as a result. |
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Classify the regenerative capacity of various tissue types in terms of continuously dividing (labile), stable, or permanent cells.
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Continuously dividing cells (epithelium): continuously dividing
Stable (all other cells): don't divide unless stimulated to Permanent cells (most neurons, cardiac muscle cells): lost their ability to replicate |
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Give a general description of the components of tissue repair involved in wound healing, including the cells, growth factors/cytokines and components of the extracellular matrix.
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5 steps to wound healing:
1) hemostasis: hemorrhage and clot formation at the site of injury. Clot forms a provisional ECM and platelets secrete mediators that favor regeneration and fibrosis, like PDGF. 2) inflammation: neutrophils and macrophages remove microbes and dead tissue. Activated macrophages also release growth factors, which initiate angiogenesis and the formation of granulation tissue. 3) regeneration: re-epithelization of the wound involves two mechanisms: MIGRATION before MITOSIS --> undamaged epidermal layer will migrate underneath the wound and undergo mitosis only once the two ends of the epithelium meet. 4) fibrosis: collagen synthesis is increased due to growth factors (PDGF, FGF, TGF-beta) and IL-1 and IL-13. Type III collagen is deposited in early wound healing. Tough type I collagen fibers are deposited in mature scars. Also, angiogenesis is stimulated by VEGF and is dependent on secretion of angiopoietins, PDGF and TGF-beta in later stages. Also, wound contraction strengthens the injured and repaired tissue and is likely mediated by fibroblasts with smooth muscle filaments called myofibroblasts. 5) tissue remodeling: the process that returns the tissue to its original structure, adn involves a balance between ECM synthesis and degradation. Matrix metalloproteinases are secreted into the healing wound and break down extra scar tissue. |
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Describe the sequence of cutaneous wound healing referred to as primary or secondary healing, as well as the factors that retard these processes.
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Primary union: clean wound with edges brought into contact. Blood clot fills the wound, scab protects against drying and bacteria. Neutrophils migrate into wound.
Day 3 - macrophages start digesting fibrin, cellular debris, RBC and angiogenesis starts. Day 5 - granulation tissue bridges defect and epidermis is regenerated Day 7 - collagen I synthesis begins Day 12 - wound at about 75% strength up to 1 year - collagen becomes more crosslinked, evolving into a scar Secondary Healing: a gaping wound. Amount of granulation tissue is greater than in primary union and wound contraction is prominent as it helps reduce the size of the defect. Bacterial contamination is inevitable. |
Factors that retard healing:
Local factors - local infection, hematoma, foreign body, denervation, blood supply, mechanical stress, necrotic tissue Systemic factors - aging, anemia, drugs (steroids), genetic disorders, malnutrition, obesity, hypoxia, vitamin deficiency, and trace metal deficiency. |
