A correlative light microscopy, transmission and scanning electron microscopy study of the ferret lung

Conducting and respiratory airways of ferrets were examined by light microscopy, transmission and scanning electron microscopy to evaluate the potential of the ferret as an animal model for studying response of inhaled irritants on the human lung. Cilia are short and longitudinal tracts of nonciliated cells interrupt the ciliary pattern in the dorsal membranous portion of the trachea. The epithelium of trachea, primary and intrapulmonary bronchi consisted of ciliated and goblet cells. Submucosal glands and cartilage were abundant down to the final distal bronchus. Brush cells and intraepithelial nerves were infrequently observed in bronchi. The distal airway unit of the ferret has a branching pattern of irregular dichotomy with one to two generations of terminal bronchioles, three to four generations of respiratory bronchioles and three to four generations of alveolar ducts. Submucosal regions of distal airways are characterized by abundant smooth muscle and connective tissue cells. Nonciliated cells with prominent apical processes are the dominant epithelial cell type of terminal and respiratory bronchioles. Infrequent clusters of ciliated cells were found interspersed among the nonciliated bronchiolar cells in first generation terminal bronchioles, whereas individual ciliated cells were infrequently observed in second generation terminal bronchioles and respiratory bronchioles. The apical portion of the nonciliated bronchiolar cell was filled with electron-lucent inclusions, smooth endoplasmic reticulum, mitochondria, and glycogen granules. Alveoli have numerous interalveolar pores and typically appearing epithelial type I, type II, and alveolar macrophage cells. The results of this study indicate that conducting and respiratory airways of ferrets are similar to those of dogs in epithelial structure, while there are minor differences in generations of terminal bronchioles and density of bronchial cartilage and submucosal glands.