Light and electron microscopical observations on the terminal airways and alveoli of the lung of the SA (Cape) fur seal Arctocephalus pusillus.

During activities of the Sea Fisheries Research Institute at Kleinzee, lung samples from six South African fur seals were collected. The terminal airways showed pseudostratified ciliated columnar epithelium with numerous goblet cells and occasional brush cells. Smooth muscle, cartilage and submucosal glands were also present. The epithelium changed over a short distance, in the smaller airways, through pseudostratified columnar non-ciliated to simple cuboidal epithelium with no goblet cells. The columnar non-ciliated cells contained secretory granules, which appeared to be serous. No Clara cells were found. Cartilage and muscle were present throughout, up to the origin of the alveolar ducts, but the glands disappeared together with the goblet cells. Alveoli were lined by types one and two alveolar epithelial cells, with subepithelial capillaries. They were divided by an alveolar septum with a well developed alveolar knob. This knob contained elastic fibres and fibroblasts, but not the smooth muscle cells which are present in terrestrial mammals and in Phocidae.