Chapter 9: Wound Healing
Which of the following is FALSE regarding polymorphonuclear neutrophils (PMNs) and their role in wound healing?
A. PMNs release proteases that degrade ground substance within the wound site.
B. Neutrophils use fibrin clot generated at the wound site as scaffolding for migration into the wound.
C. Neutrophil migration is stimulated by local prostaglandins, complement factors, interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), platelet factor 4, or bacterial products.
D. PMNs are the first cells to infiltrate the wound, peaking at 24 to 48 hours.
E. Neutrophils release cytokines that later assist with collagen deposition and epithelial closure.
Polymorphonuclear neutrophils (PMNs) are the first infiltrating cells to enter the wound site, peaking at 24 to 48 hours. Increased vascular permeability, local prostaglandin release, and the presence of chemotactic substances such as complement factors, interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), platelet factor 4, or bacterial products all stimulate neutrophil migration.
The postulated primary role of neutrophils is phagocytosis of bacteria and tissue debris. PMNs are also a major source of cytokines early during inflammation, especially TNF-α, which may have a significant influence on subsequent angiogenesis and collagen synthesis. PMNs also release proteases such as collagenases, which participate in matrix and ground substance degradation in the early phase of wound healing. Other than their role in limiting infections, these cells do not appear to play a role in collagen deposition or acquisition of mechanical wound strength. On the contrary, neutrophil factors have been implicated in delaying the epithelial closure of wounds. (See Schwartz 10th ed., p. 243.)
The proliferative phase of wound healing occurs how long after the injury?
Normal wound healing follows a predictable pattern that can be divided into overlapping phases defined by the cellular populations and biochemical activities: (1) hemostasis and inflammation, (2) proliferation, and (3) maturation and remodeling.
The proliferative phase is the second phase of wound healing and roughly spans days 4 through 12. It is during this phase that tissue continuity is reestablished. Fibroblasts and endothelial cells are the last cell populations to infiltrate the healing wound, and the strongest chemotactic factor for fibroblasts is platelet-derived growth factor (PDGF). Upon entering the wound environment, recruited fibroblasts first need to proliferate, and then become activated, to carry ...