Chapter 9: Wound Healing Flashcards
Name the phases of wound healing?
Inflammatory (early 24-48hr, late 48-72hr)
Proliferative (day 4-12)
- Contraction (soon after the granulation bed is established (dog day 4.5? cat later)
- Epithelization (on the edge of wounds it begins within hours)
Maturation (months)
Wound hypoxia impairs resistance to infection – oxygen partial pressure below ___mmHg is associated with an inability of neutrophils to kill bacteria?
40mmHg
By 48-96 hours what is the primary leukocyte?
Macrophage - they microdebride the wound, phagocytose degenerate neutrophils and induce neutrophil apoptosis
Lymphocytes are attracted to the wound by which cytokine?
IL-1 at day 3-5
Capillary endothelial response to VEGF is dependent on what?
oxygen dependent
arterial partial pressure of oxygen (PaO2)
Fibroblasts transform into myofibroblasts in response to what cytokine?
TGF-B1
Initial collagen formation in a wound is mostly what type?
By the maturation phase it is mostly what type?
Type 3
Type 1
final strength of the scar is what % of unwounded tissue?
70-80%
the submucosa of the GIT is predominately what type of collagen?
Type 1 (68%)
Fibroblasts in the GIT differ from that of the skin in that they?
Also produce elastin (skin fibroblasts only produce collagen)
Anastomosis strength in the first few days of healing decreases by what percent in each tissue?
Esophagus
Gastroduodenal
SI
Colon
esophagus 37%
gastroduodenal 64%
small intestine 70%
colon 72%
Sepsis causes an upsurge in what activity causing an increased risk of dehiscence?
Collagenase activity
Name 4 factors which differ between healing of skin and GIT?
collagenase activity (skin not significant, GIT increased days 0-3, causes decreased anastomotic strength)
production of collagen (fibroblasts in skin, GIT smooth muscle cells and fibroblasts)
wound shear stress (skin variable, GIT increased due to peristalsis and intestinal motility)
vascular perfusion (relatively constant in skin / GIT can be significantly downregulated by shock)
collagen types (skin 1,3 / git 1,3,5)
bacterial flora (skin aerobia, not widely polymicrobial / GIT aerobic and anaerobic and polymicrobial)
Mature collagen formation fails when PaO2 is below what mmHg?
40mmHg
Bladder re-epithelization occurs in how many days?
2-4 days
Bladder regains 100% of its unwounded strength within how many days?
21 days
collagen synthesis not normal until day 70 postinjury
Breaking strength of cutaneous wounds at 7 days significantly less in cats or dogs?
in Cats
Granulation tissue is seen earlier in which species?
Earlier in dogs
and canine wounds produce more granulation tissue than cats
Contraction and epithelization is faster in which species?
dogs - Mean time to complete granulation tissue bed in canine wounds was 7.5 days and in cats was 19 days
At 14 days what % of canine wounds are epithelialized compared to just 13% of cats?
44%
Which breed is prone to fibroproliferative scarring?
Mexican hairless dog
Animals with an endocrinopathy are how many times more likely to develop a postop infection?
8.2 x
How do glucocorticoids affect wound healing?
Impair macrophage activity, fibroblast proliferation and collagen synthesis and inhibit synthesis of MMP
The trunk and neck heal mostly by what way?
contraction
What types of collagen are in the skin? In the GIT?
1,3 in the Skin
1,3,5 collagen in GIT
Everything in the GIT except esophagus and distal 1/3 of rectum has how many layers? What are they?
4 layers: mucosa, submucosa, muscularis propria, serosa
What percent of each type (1,3,5) of collagen are present in the submucosa of the GIT?
Type 1: 68%
Type 3: 20%
Type 5: 12%
Unwounded skin contains what % of type 1 and Type 3 collagen?
Type 1: 80%
Type 3: 20%
What cells secrete MMPs to break down extracellular matrix and allow cell migration during the epithelialization phase of healing?
Keratinocytes
How does wound contraction occur?
In the granulation bed, anchored fibroblasts become myofibroblasts due to TGF-B1
These cells have increased alpha smooth muscle actin and stress fibers
They orient linearly along the line of tension and start pulling
How does angiogenesis occur?
Growth factors released in inflammatory phase act on capillaries to increase endothelial cell proliferation -> the cells make tubules -> these are new capillaries
Collagen production in wounds is rapid for the first how many weeks?
6 weeks - goes down without orientation, then next 12-18 months it aligns/matures
Most bone fractures heal through what two types of ossification?
Combo of intramembranous and endochondral
The strength of an anastomosis decreases significantly within what timeframe?
First 48hr due to collagenases
Platelets bind to vWF on collagen exposed in wounded tissue. They then release what?
Thromboxane A2
