A light and electron microscopic study of the respiratory epithelium of the adult aquatic newt, Notophthalmus viridescens

Light microscopy reveals that the non-partite lung of the fully aquatic adult newt, Notophthalmus viridescens, possesses four distinct types of epithelium: (1) pseudostratified columnar ciliated epithelium with goblet cells, (2) simple squamous epithelium, (3) simple cuboidal to columnar epithelium, and (4) vascularized epithelium with columnar-shaped cells.The pseudostratified columnar ciliated epithelium is distributed as a narrow band of tissue which extends nearly the entire length of the elongated lung on the dorsal or ventral aspects in close association with large pulmonary blood vessels. At the margins of this tissue, simple columnar, cuboidal, or squamous epithelium can occasionally be observed. Vascularized epithelium with columnar-shaped cells is the most prevalent of the four epithelia and lines the rest of the lung surface. Structures of particular importance present in these columnar cells are lamellated, osmiophilic, perinuclear bodies resembling cytosomes. Electron microscopy demonstrates that attenuated cytoplasmic projections extend laterally from the apical surfaces of adjacent columnar cells and are attached to one another by desmosomes. Thus, the columnar-shaped cells of the vascularized epithelium in the adult newt appear to be functioning not only as type I cells of mammals in that they form a continuous epithelial lining at the surface of the lung, but also as mammalian type II cells since they possess cytosomes.