Microscopic anatomy of the ringed seal (Phoca hispida) lower respiratory tract.

The microscopic anatomy of the ringed seal lung exhibits unique features and many features similar to those described in other seal species. Unique features include: Trachealis muscle predominately oriented longitudinally; Large veins within the tracheal wall supported by elastic fibers; Goblet cells and pseudostratified epithelium lining the duct system of bronchial glands of the segmental bronchi; Lamina propria of the segmental bronchus heavily invested with elastic fibers clustered into dense longitudinal bundles; and Capillaries and venules covered with squamous epithelium protruding into bronchiolar lumina. Common features include: Cartilage support of the bronchial tree extending distally into respiratory bronchioles; Smooth muscle enhancements in the distal airways producing sphincter like formations; and Lungs extensively supported with interstitial tissue, which divide lungs into lobules.