The lung of the common toad, Bufo arenarum (Anura: Bufonidae). A light and electron microscopy study

RESUMO

The present study describes the lung morphology of the common toad, Bufo arenarum, as observed by light and electron microscopy. The lung wall consists of four layers: mesothelium, dense connective tissue with thin elastic fibers, loose connective tissue containing smooth muscle fibers and an internal respiratory epithelium. The lung presents three types of folds defined by their epithelia. First order folds are coated by ciliated epithelium containing numerous goblet cells. Second order folds present the same type of epithelium but devoid of goblet cells, while third order folds are only lined by respiratory epithelium. The respiratory surface of the lung is lined by a single cell type, the pneumocyte, which presents characteristics of both type I and type II alveolar cells of higher vertebrates. The pneumocytes are prismatic in shape and possess attenuated cytoplasmatic processes which spread over the pulmonary capillaries to form the outer layer of the air-blood barrier. These cells present microvilli in the apical extreme and contain different types of cytoplasmic bodies: electron dense, multivesicular and lamellar