Chapter 8 

 WOUND HEALING AS A PROBLEM OF GROWTH^ 



Wesley W. Washburn Jr. 



I. INTRODUCTION 



The creation of a wound initiates an immediate series of events directed toward 

 closing the defect. No Hving organism will tolerate such an interruption of body 

 continuity without attempting repair. The loss of epithelium and its subjacent 

 components not only exposes the animal to bacterial invasion but also allows the 

 escape of body fluids essential for its well being. Methods used to overcome this 

 crisis are infinitely variable but can be summarized into two general processes. 

 In the lower invertebrates, a simple redistribution of cells is common. This 

 phenomenon, called morphallaxis, ultimately results in a change in body form 

 (Needham, 1952), however the most frequent mode of repair is epimorphysis, 

 a direct regrowth of tissue at the wound site. The phylogeny of the organism seems 

 to bear little relationship to its method of healing since many protozoa and 

 coelenterates heal by epimorphysis similar to mammals. Furthermore, epimorphic 

 healing is always associated with migration of cells and an increase in their num- 

 ber; hence morphallaxis, to a certain degree, is present in all healing processes. 

 Two distinctly different types of epimorphic healing can occur, and the final 

 structure is entirely dependent upon which takes place. The terminology is 

 confusing in this respect because much emphasis has been placed upon the 

 similarity rather than upon the basic differences between these processes. In this 

 chapter they will be designated as regeneration and as wound healing. The 

 essential difference is the presence of pluripotent cells at one period during 

 regeneration. The stages of regeneration are: wound closure, dedifferentiation, 

 formation of a blastema, induction of the Ijlastema and subsequent growth to 

 form the missing part. On the other hand, the stages of wound healing are: 

 clot formation, invasion of the area by phagocytic cells, proliferation of locally 

 available differentiated tissue, epithelialization, and, ultimately, remodeling of 

 the area to form a stable scar. Regeneration in the above sense is unknown in 

 mammals; wound healing is the only recourse available. There is little evidence 

 at present to suggest the existence of pluripotent cells during any stage of wound 



^ Department of Surgery (Plastic and Maxillofacial), The University of Texas Medical 

 Branch, Galveston, Texas. Supported by U. S. Army Contract DA-49-007-MD-447. 



