AN SEM AND TEM STUDY OF THE TRANSITION OF THE BRONCHUS TO THE PARABRONCHUS IN QUAIL (COTURNIX-COTURNIX)

The main objective was to analyse the transition of the bronchus to th e parabronchus in birds and to describe its specific structure in an i ntegrated light microscopic, transmission electron microscopic (TEM) a nd scanning electron microscopic (SEM) study. Lung tissue from immatur e and mature quail was subjected to standard processing for paraffin l ight microscopy, TEM and SEM after intratracheal inflation with fixati ve. In transverse paraffin and Durcupan semithin sections, the partiti on incompletely closing the broncho-parabronchial transition has the a ppearance of a crest-like fold delineating the entrance to the underly ing parabronchial vestibulum. The core of the entrance fold is compose d of loose connective tissue with free cells, and has a well-developed blood supply and innervation Voluminous groups of smooth muscle cells are interconnected with those of neighbouring entrance folds and the interatrial septa. On the parabronchial surface and partly on the bron chial surface the entrance fold is invested with simple cuboid epithel ium consisting exclusively of granular cells with lamellar inclusions. On the bronchial surface, they pass into ciliated columnar pseudostra tified epithelium. At the root of the parabronchially orientated surfa ce, they continue into the mixed population of granular and squamous a trial cells of the parabronchus. Among the granular cells of the entra nce fold, scattered epithelial neuroendocrine cells are consistently p resent. The three-dimensional visualization demonstrated the oval form of the entrance window with a circular field of non-ciliated cells de lineating the entrance to the parabronchial labyrinthine system. The g eneral structural pattern of the entrance fold, together with the comp lex system of interatrial trabecles of the parabronchi underline the m ultifactorial function of complex system submitted to the skeletal, re gulatory and host defense of the gas exchange tissue.