674 



WOUND HEALING 



IV. EPITHELIALIZATION 



The creation of a skin defect initiates an "effort" on the part of the adjacent 

 epithehvim to cover the denuded surface and the degree to which this is successful 

 depends upon the size of the defect. Superficial abrasions involving only epidermis 

 or upper portions of the dermis are rapidly healed by replacement from the basal 

 and Malpighian layers or, in the case of dermal involvement (split-thickness skin 

 graft donor sites), from epithelium of the glands and hair follicles in the dermis 

 (Brown and McDowell, 1942, 1949; Pepper, 1954; Gillman et al., 1954). 



Wounds, consisting of sharply incised edges with no loss of tissue, heal by 

 re-approximation of contiguous borders. Gillman, Penn, Bronks, and Roux (1956) 



..J^^ 



Fig. 5. Photomicrograph of an eight-day old rat burn showing the column of newly formed 



reticulin fibers which extends into the subcutaneous layers (Gomori reticulin stain, X24). 



Ret — reticulin; Ep — epithelium 



have demonstrated that in such wounds epithelium inverts into the incision and 

 migrates along the cut edges of the dermis. The subsequent growth of dermal 

 elements results in detachment of many of these epithelial spurs from the overlying 

 epithelium and ultimately the formation of keratinizing epithelial pearls. Eventually 

 the migrating epidermal edges contact one another and fuse. The mechanism of 

 this fusion is unknown, although some information now exists concerning the 

 normal morphology of epithelial cell boundaries. Selby (1955) has demonstrated 

 with the electron microscope that cell membranes of human skin are joined by a 

 series of bridges separated by intercellular spaces. Cytoplasmic filaments, which 

 most probably represent the keratin-like fibrous protein, "epidermin" of Rudall 

 (1952), do not cross these intercellular bridges but are connected by a series of 

 rod-shaped granules of alternating density. 



The following steps are required for epidermal healing: {a) Retraction of the 



