Flashcards in Wound healing Deck (22):
What processes must occur during wound healing?
regeneration and repair
What is regeneration? On what does regeneration depend? What are the categories of tissues that are relevant to regeneration?
regeneration is the replacement of damage tissue with native tissue. it depends on the capacity of the tissue to regenerate. Tissues may be labile, stable, or permanent
examples of labile, stable, and permanent tissues. Where are the stem cells?
Labile: skin (stem cells in basal layer) and small and large bowel cells (stem cells in mucosal crypts), and bone marrow (hematopoeitic stem cells
Stable: cells aren't overturning constantly, but the tissue does have regenerative capacity. Most cells are in quiestant G0 stage but can reenter the cell cycle. Examples: liver
Permanent tissues lack significant regenerative capacity: heart, neuron, skeletal muscle,
What is the goal/definition of repair?
tissue repair is defined as the replacement of damaged tissue with a fibrous scar. this process occurs when the skin cells are lost (ex. deep skin cut) or when a tissue lacks regenerative capacity
What happens during the initial phase of tissue repair? What are the important players (cells and structures)
formation of granulation tissue
granulation tissue consists of fibroblasts to deposit type III collagen, capillaries to provide nutrients, and myofibroblasts to contract the wound
What happens during scar formation? What chemicals/proteins are critical for this process
type III collagen is replaced with type I collagen
collegenase removes type III collagen and requires a zinc cofactor
What are the differences btw type III and type I collagen?
type III collagen is pliable and present in granulation tissue, embryonic tissue, the uterus, blood vessels, and keloids
type I collagen has high tensile strength and is present in skin, bone, tendons, and most organs
What are the biochemical underpinnings of tissue regeneration and repair?
tissue regeneration and repair is mediated by paracrine signaling via growth factors. interactions of growth factors with receptors result in gene expression and cell growth.
What does TGF-a do?
epithelial and fibroblast growth factor
what does TGF-b do?
fibroblast growth factor. inhibits inflammation
What does platelet derived growth factor do?
(PDGF) growth factor for endothelium, smooth muscle, and fibroblasts
What does fibroblast growth factor do?
important for angiogenesis. also mediates skeletal development
What are the ways in which cutaneous healing might occur? how are they different?
primary or secondary intention
1. primary: wound edges are brought together, leading to minimal scarring (ie. after surgical incision)
2. secondary: edges aren't together. granulation tissue fills the defect and myofibroblasts contract the wound to form a scar. important to remember that the granulation tissue contracts the wound, because of the myofibroblasts
What are some causes for delayed wound healing?
1. infection: most common cause
2. vitamin C, copper, or zinc deficiencies
3. other: foreign bodies, ischemia, diabetes, malnutrition
Why does vitamin C deficiency cause a delay in wound healing?
vitamin c is needed for hydoxylation of proline and lysine procollagen residues. hydroxylation is necessary for collagen cross-linking
remember normal collagen structure: collagen is normally Glycine-X-Y. X and Y are usually proline or lysine. Y is often pro/ or lys. Y will get hydroxylated (will have an OH added). This OH group allows crosslinking with other OH groups on other collagen fibers: allows the collagen to strength.
Why does copper deficiency cause a delay in wound healing?
Cu is a cofactor for lysyl oxidase, which cross-links lysine and hydroxylysine to form stable collagen
Why does zinc deficiency cause a delay in wound healing?
zinc is a cofactor for collagenase, which replaces type III collagen, which forms part of granulation tissue, with type I collagen, which is stronger.
What is dehiscence?
rupture of a wound, most commonly seen after abdominal surgery
What is a hypertrophic scar?
excess production of a scar that is logalized to the wound
What is keloid? Who gets it? Where on the body is it seen?
excess production of a scar that is out of proportion to the wound. it is characterized by excess type III collagen and is most common in African Americans (genetic predisposition) Classically seen in earlobes, face, and upper extremities.
What is the marker of the hematopoeitic stem cells?