THE CYTOLOGY OF WOUND HEALING OF BODY SURFACES IN MAMMALS

Abstract

SUMMARY 1 The cytological aspects of the repair of wounds with loss of substance in the skin, cornea and a number of mucous, serous and synovial membranes in mammals (laboratory animals and man) have been reviewed. 2 It is emphasized that, as in the last century, the majority of studies of wound healing continue to be carried out on skin, and the need for examining repair processes in other organs is stressed. 3 While most of the evidence indicates that epithelium regenerates from old epithelium at the wound margin, the surfaces of serous and synovial membranes are probably repaired by metaplasia of underlying connective tissue cells, assisted by the implantation of islands of surface cells that have desquamated from adjacent surfaces. 4 The epithelia of the gall-bladder and urinary bladder (in the cat) display abundant evidence of mitosis in migrating cells. Mitosis in spreading cells has also been observed in ileal and rectal epithelium. 5 While migration remains a primary factor in epithelial repair, the role of mitosis has possibly been underestimated in the past. 6 The origin of the connective tissue cells of granulation tissue remains an enigma. There is evidence suggesting that the fibrocytes of the dermis do not proliferate, and that new connective tissue cells are haematogenous in origin. 7 The endothelial (vascular and lymphatic) elements of granulation tissue originate by budding from pre-existing vessels. There is doubt whether mitosis occurs in such endothelial cells. 8 In the repair of mucous membranes in the alimentary tract, new gland formation is observed regularly in the stomach, duodenum and ileum in all the species that have been investigated, including man. The colon and rectum appear to exhibit less regenerative capacity than higher levels of the alimentary tract, for there is no consistent evidence for new gland formation in these viscera. 9 No universally applicable explanation is yet forthcoming for the accumulation of glycogen that can be detected histochemically in many, but not all, of the regenerating epithelia that have so far been studied. 10 Among the urgent items on which cytological research might be prosecuted in the future are: the possible role of metaplasia of connective tissue cells in the production of new epithelium, mitosis in migrating epithelium, the factors regulating the initiation and cessation of mitosis, the problem of the origin of new connective tissue cells, and the causes of contraction. Compared with the number of purely morphological studies, histochemistry and autoradiography have not often been wedded to the problems of repair, while the whole field of wound healing at the cellular level awaits study with the electron microscope.