Changes

*The bronchioles have no cartilage rings but have well developed muscular walls to enclose the lumen. The epithelium is reduced to cuboidal, and in the normal animal it contains no mucus secreting glands. There are many lymphoid nodules beneath the epithelial layer.

*The bronchioles have no cartilage rings but have well developed muscular walls to enclose the lumen. The epithelium is reduced to cuboidal, and in the normal animal it contains no mucus secreting glands. There are many lymphoid nodules beneath the epithelial layer.

*Respiratory Bronchioles have few alveoli scattered along the length, at the entrance of which is ''simple squamous'' epithelium, and bronchial smooth muscle bundles.

*Respiratory Bronchioles have few alveoli scattered along the length, at the entrance of which is ''simple squamous'' epithelium, and bronchial smooth muscle bundles.

==Species Differences==

==Species Differences==