Healing & Repair Flashcards
What are the possible outcomes of cell injury?
- adaptation
- repair
- death
List mechanisms of repair.
- regeneration
- regeneration by connective tissue (scar formation)
- both
Characterize regeneration repair.
- occurs when connective tissue is still intact => serves as scaffolding
- replacement by same cell type
- mild injuries
Characterize scar formation repair.
- occurs when connective tissue has been injured or injured cells do not have regenerative capabilities
- replaced with collagen
- severe injuries
Define labile cells.
- continuously dividing
- easily regenerate
- ex: epithelium, mucosal linings
Define stable cells.
- fixed in G0 stage
- can regenerate when stimulated by growth factors to re-enter cell cycle
- ex: liver, kidney, smooth muscle
Define permanent cells.
- cannot regenerate
- cardiac, muscle, neurons
List components of scar formation (reparation by connective tissue)
- angiogenesis
- fibroblast proliferation
- ECM deposition (by fibroblasts)
- organization of fibrous tissue element
Which growth factor is an important mediator of angiogenesis? minor mediators?
- VEGF
- PDGF, TGF-B, FGF are minor
Which growth factors are important mediators of fibroblast proliferation?
- PDGF, FGF, TGFB
Define granulation tissue. What are the components?
- in between stages of injury and scar; only present during healing
- fills in defects where cells are non-regenerative or CT framework is destroyed
- appears red and edematous
Components
- proliferating fibroblasts
- immature CT
- angiogenesis
Define the process of organization.
- transforming granulation tissue into a scar
- over time, granulation tissue transforms to mature CT (collagen)
- blood vessels become less prominent
List the steps in healing a skin laceration.
- injury
- inflammation
- blood clot (fibrin, fibronectin)
- regeneration of epithelium
- proliferation of fibroblasts, myofibroblasts, and macrophages in the defect
==> fibroblasts lay down collagen
==> myofibroblasts pull wound edges together
==> macrophages clean up debris, secrete cytokines - angiogenesis
- over time, granulation tissue becomes filled with collagen, parenchymal cells, and acquires strength via vitamin C.
Describe healing by first intention (primary union).
- wound is clean and inspected immediately
- defect is small and limited
- gap is closed with sutures, cleaned, and debrided
Describe healing by second intention (secondary union).
- wound is large, infected, and patient has not been seen
- no sutures; allow wound to granulate
- clean and debride
- occurs internally on organs as well
- takes longer
How do the following local factors affect inflammation:
- vascular supply
- infection
- foreign bodies
- ionizing radiation
- vascular supply: adequate blood supplied required for inflammation and healing; low blood flow = takes longer to heal, more prone to infection
- infection: bacteria continues to incite inflammation…takes longer to heal
- foreign bodies: intensifies inflammation and takes longer
- ionizing radiation: decreases vascular supply..takes longer
How do the following systemic factors affect inflammation:
- circulation
- infection
- nutrition
- hormones
- circulation: poor circulation (CHF) impairs transport of O2, inflammatory cells, growth factors…takes longer
- infection: overwhelms immune system…takes longer
- nutrition: poor nutrition => deficiencies in wound healing factors (proteins, vitamin C, copper, zinc)
- hormones: steroids inhibit inflammatory process…impaired healing (meds or cushing’s)
List vitamins and mineral required for adequate wound healing and their roles.
- vitamin C: collagen cross-linking
- copper: cofactor for enzyme required for collagen cross-linking
- zinc: cofactor for collagenase to break down collagen and keep building
List complications of scar healing.
- defective scar formation: dehiscence, incisional hernia
- excessive scar formation: keloids, hypertrophic scars
Define dehiscence.
rupture of wound due to:
- mechanical factors
- infection
- ischemic necrosis
Define keloids.
accumulation of excess collagen beyond wound boundaries
- hereditary
- more common in african-americans
Define hypertrophic scars.
excessive collagen deposition inside wound boundaries
- may regress
Define ECM. List protein components.
network of interstitial proteins made of matrix and basement membranes
- fibrous structural proteins: collagen, elastins
- water hydrated gels; proteoglycan, hyaluranons
- adhesive glycoproteins
List pros and cons of scar formation.
pros - allows organ to keep functioning
cons - that particular region where the scar is no longer functions
Define VEGF.
Vascular Endothelial Growth Factor
- promotes angiogenesis, endothelial cell migration/proliferation, and increased vascular permeability
- low levels in adults
- high levels in glomerulus and retina
- induced by hypoxia (angiogenesis can reperfuse an area during hypoxia)
- if mutated, defective angiogenesis
Describe the timeline of wound healing.
- after 1 week, 10% strength regained
- after 3 months, 70-80% strength regained
never 100%
Define fibrosis.
excessive collagen deposition in a tissue
Define contracture.
- typically in burns
- excessive contraction can lead to skin being fixed in a tight position
