CHAPTER 9
Wound Healing
Test Taking Tips
• Questions tend to revolve around physiology of how wounds heal, that is, secondary intention, myofibroblasts, and which cells are involved in wound healing.
• The strength layer of bowel/skin is also commonly tested. One should also be familiar with which organs lack certain tissue layers such as the esophagus with no serosa and where the posterior rectus sheath starts/stops.
Name the 3 phases of wound healing:
Inflammation (1–6 days), proliferation (3 days–3 weeks), maturation (3 weeks–1 year)
Name several factors that can inhibit wound healing:
Diabetes, infection, ischemia, malnutrition, radiation, steroids, neoplasia, anemia
What are the optimal nutrition parameters?
Albumin >3 g/dL and prealbumin >16 mg/dL
What is primary wound closure (primary intention)?
Immediate closure of a wound with suture or staples
Most important factor in healing closed wounds by primary intention:
Tensile strength
What is the most important layer to close for strength in skin lacerations?
Dermis
How long does it take a surgical incision become “water tight”?
24 to 48 hours
What is secondary wound closure?
Leaving a wound open and allowing it to heal by granulation, contraction, and epithelialization over time
Most important factor in the healing of open wounds by secondary intention:
Epithelial integrity
What causes contraction in wounds healing by secondary intention?
Myofibroblasts
What is delayed primary closure?
Closing a wound several days (3–5 days) after incision
Rate of regeneration of a peripheral nerve:
1 mm/d or 1 in./mo
Rate of epithelialization:
1 to 2 mm/d
The strongest layer of the bowel:
Submucosa
The time period that a small bowel anastomosis is at its weakest:
3 to 5 days
Name the 2 major events in the process of epithelialization:
Migration and mitosis
Name the process by which keratinocytes pile up on top of each other at the leading edge of a migration and tumble forward over the top of the heap:
Epiboly
What cell is the most essential for wound healing?
Macrophage
This cell is responsible for the movement and contraction of wound edges:
Myofibroblast
Name the order of arrival of the different cells involved in wound healing:
Platelets (not a true cell)
Neutrophils (predominant cell type from day 0–2)
Macrophages (predominant cell type from day 3–4)
Fibroblasts (predominant cell type from day 5 and so on)
Lymphocytes
Platelet factor 4, β-thrombomodulin, PDGF, and TGF-β are contained in this type of platelet granule:
α granule
Adenosine, serotonin, and calcium are contained in this type of platelet granule:
Dense granule
Name the predominant cell during days 0 to 2 of wound healing:
Neutrophils
Name the predominant cell during days 3 to 4 of wound healing:
Macrophages
Name the predominant cell present after day 5 of wound healing?
Fibroblasts
When does the maturation phase usually begin?
~3 weeks after the injury
What is the maximal tensile strength that a wound can reach?
80% of original tissue strength
Time period for maximum collagen accumulation in a wound:
2 to 3 weeks (mostly type III, then gets converted to type I with maturation)
FIGURE 9-1.
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