Less Common Cell Types in the Tracheal Epithelium

T~Sik, 1.: Less Common Cell Types in the Tracheal Epithelium of Reptiles. Acta vet. Brno, 61,1992: 17-22. Tracheal epithelium of representatives of21 reptile species of 10 families was found to consist of several cell types. The first in the order of frequency were ciliated, goblet and granular cells followed by their considerably fewer precursors basal cells, and rare intermediary cells. Plasma cells and Kultschitzky cells were found very rarely in the basal layers of the epithelium. No evidence was obtained to indicate the presence of Clare cells and brush cells as have been described in mammals. Tracheal epithelium, basal cell, intermediary cell, plasma cell, Kultschitzkr cell The morphology of the lung epithelium of reptiles has been the subject of numerous studies. The structure of their tracheal epithelium, on the other hand, has received little attention. Light microscopic observations on the tracheal epithelium of the common lizard (Lacerta al!ilis I have been reported by Krause (1922). According to him it is made up of ciliated cells among which goblet-shaped elements can be found. The ultrastructure of the tracheal epithelium in a number of other reptile species has been described by THik (1978, 1980, 1981, 1982, 1984a, b, 1986), THik and Nedved (1976) and THik and Antalikova (1984). The most frequently occurring cell types in their studies were ciliated,granular and goblet cells. Their mutual numerical proportions vary with the order or family of the reptiles examined. The incidence of goblet and granular cells is governed by the law of reciprocity (THik 1978, 1982, 1986). In the tracheal epithelium of the Gekkonidae and the Lacel·tidae, e. g., secretory cells are represented only by granular elements (Tesik 1984,; TeSik and Nedved 1976). In the phylogenetic classification of reptiles typical mucinous cells in the trachea do not occur until in the Anguidae, along with still predominating granular cells. It is only in the Te.'tudinata, Loricata, Ophidia and the Varanidae that goblet cells show a marked predominance in the tracheal epithelium. It can be said that their proportion increases with the decreasing proportion of granular cell. Ciliated cells occur only singly or in small clusters in the Gekkonidae. In the epithelium of the Lacertidae, Agamidae, Scincidae, Anguidae and the Testudinidae ciliated cells are more numerous, covering fairly large areas. On the other hand, the inner surface of the trachea in snakes, crocodiles and monitors is lined with an epithelium consisting substantially of ciliated cells, while the elements of secretory character, i.e. granular and goblet cells, are in the minoritY, occurring either singly or in more or less large clusters (TeSik 1978, 1982). Ciliated cells in reptiles show the basic morphological pattern as known in other vertebrate classes, although they may be markedly flattened. In consequence, the nucleus is then elongated and its long axis runs parallel to the basement membrane. The intercellular spaces between ciliated cells are larger than in birds and mammals, particularly in the basal parts of the epithelium. Also the interdigitations between adjacent cells are more numerous and more complex. The cilia of these cells are vigorous, growing from massively developed basal b:>dies. Striated rods below the blepharoplasts are long and show marked striation. Also the microvilli between the cilia are vigorous and branch fairly frequently. The cristae of the mitochondria of the subciliary zone of ciliated cells are often disposed irregularly and, more frequently than in birds and mammals, do not run perpendicularly to the long axis of the mitochondrion (Tesik 1980).