Macroscopic and microscopic study of trachea in Caspian seal (Pusa caspica)

In this study, performing for the first time, the tracheas of 5 Caspian seals were examined. For macroscopic study, the appearance features of the tracheas and the position of their cartilaginous rings were carefully examined. For microscopic examination, after the usual histological procedures, 6-micron sections were prepared and stained with hematoxylin-eosin, periodic acid Schiff, Masson's trichrome, Verhoeff and Alcian blue and studied with a light microscope. The macroscopic results showed that the tracheal lumen was elongated in an oval shape, but in the anterior surface of the trachea the cross section was completely round. The cartilaginous rings are C-shaped, but the cartilages located caudal to the cricoid cartilage appear as complete rings. The number of cartilaginous rings in 5 samples was between 85 and 95 cartilages, and their complete rings are about 28. The histological results showed that the epithelium is pseudo stratified columnar with many goblet cells. The lamina propria consists of loose connective tissue containing dense lymphatic tissues and the submucosa is composed of dense connective tissue. The presence and density of the collagen and elastic fibers in the submucosa seem to be higher than in the lamina propria, and a wide vascular network with lacunal spaces and valve-like structures can be seen in the connective tissues of the trachea. The muscles of the trachea are mainly oriented in the longitudinal direction and the cartilaginous rings in the dorsal region of the trachea overlap in several layers.