Wound Healing Flashcards
What is regeneration?
Damaged tissue replaced with native tissue
What are the 3 ways tissues can be divided in terms of their regenerative capacity?
- Labile tissues - continuously cycle to regenerate tissue
- Stable tissues - quiescent but can reenter cell cycle
- Permanent tissues - lack regenerative potential
What are examples of labile tissues (continuously cycle to regenerate tissue)?
- Small and large bowel (stem cells in mucosal crypts)
- Skin (stem cells in basal layer)
- Bone marrow (hematopoietic stem cells)
What are bone marrow stem cells cluster of differentiation +ve?
CD34+
What is an example of a stable tissue that can reenter cell cycle?
Liver
- each hepatocyte can renter cell cycle
PCT of kidney
What are examples of permanent tissues? (lack regenerative potential)
- Myocardium
- Skeletal muscle
- Neurons
What is repair as opposed to regeneration?
Repair replaces damaged tissue with fibrous scar
- Occurs when regenerative stem cells are lost (e.g. scar deep enough to damage basal layer) or when tissue lacks regenerative capacity (permanent tissues)
What is the initial phase of repair of a scar?
Formation of granulation tissue
What are the 3 components of granulation tisssue?
- Fibroblasts (deposit T3 collagen)
- Capillaries (provide nutrients)
- Myofibroblasts (contract wound)
What is type 3 collagen replaced with in a scar?
Type 1
What enzyme removes type 3 collagen?
What does it require as a cofactor?
Collagenase
- Requires zinc as a cofactor
Where can T3 collagen be found?
- Blood vessels
- Granulation tissue
- Embryonic tissue
V. pliable
Where is T4 collagen seen?
BM
What type of collagen is initially deposited in a scar and what is it then replaced with?
Type 3 collagen, replaced with type 1
What is TGF-alpha a growth factor for?
Epithelium and fibroblast
What is TGF-B a growth factor for?
Fibroblast growth factor; inhibits inflammation
What is PDGF a growth factor for?
- Endothelium
- SM
- Fibroblast growth factor
What is FGF a growth factor for?
- Angiogenesis
- Skeletal development
What is VEGF a growth factor for?
Angiogenesis
What are the 2 mechanisms through which cutaneous healing can occur?
Describe them
Primary or secondary intention
Primary
- Wound edges brought together; minimal scar formation
Secondary
- Edges are not approximated; granulation tissue fills in the defect
What are causes of delayed wound healing outside of infection?
- Vit C (hydroxylation)
- Copper (lysyl oxidase - involved in cross linking
- Zinc deficiency
- Foreign body
- Ischemia
- Diabetes
- Malnutrition
What amino acids make up collagen?
- Glycine
- Proline
- Lysine
What does Vit C do to collagen?
Hydroxylates proline or lysine
- Allows cross linking between collagen molecules
What does zinc do in scar formation?
Cofactor for collagenase which removes type 3 replaces with type 1
How can copper deficiency affect wound healing?
Require for formation of :
- Lysyl oxidase - involved in cross linking collagen molecules
What is dehiscence ?
When does it commonly occur?
Rupture of wound - most commonly seen after abdo surgery
What is a hypertrophic scar?
Excess production of scar tissue localized to wound
What is a keloid and what is it due to?
- Excess production of scar tissue that is out of proportion to the wound
- Characterised by excess type 3 collagen
What group is more likely to get keloid?
African Americans
Where does keloid typically affect?
Earlobes, face and upper extremities
