The respiratory bronchiole of beagle dogs: structural characteristics

The centriacinar regions are a central site of lung diseases and they are also considered to be susceptible to air pollutants. Dogs as well as humans and monkeys possess several generations of respiratory bronchioles. Commonly used small laboratory animals, however, have either no, or at most, a single short generation. Therefore, it is assumed that the response to air pollutants differs among animal species according to the presence or absence of the respiratory bronchiole. Although the conducting airways and alveolar regions have been well examined, morphological details of the respiratory bronchiole remain to be elucidated. To better understand the architecture of the respiratory bronchiole, we investigated this region of beagle dogs by means of serial sections of paraffin tissues. This study shows that respiratory bronchioles of beagle dogs consist of up to five generations. Branching patterns of the respiratory bronchiole of beagle dogs were comparable to those of humans. The surface of the respiratory bronchiole is comprised of the bronchiolar epithelial lining and alveolar outpocketings. The lining cells of beagle dogs are mainly nonciliated cells (Clara cells) whereas ciliated cells are very rare.