Light microscopic and immunohistochemical study of the trachea of the broad-snouted caiman (Caiman latirostris)

The purpose of this study was to examine the tracheal structure of the crocodile Caiman latirostris using light microscopy, histochemical and immunocytochemical techniques. The tracheal epithelium of C. latirostris consists of a ciliated pseudostratified columnar epithelium with goblet cells. The respiratory epithelium also includes endocrine cells immunoreactive to serotonin. The histochemical techniques demonstrated the presence of neutral and sulphated mucins secreted by goblet cells. The lamina propria consists of connective tissue with many reticular fibres. The elastic fibres are interspersed among collagen bundles, forming the border between the mucosa and the submucosa. The submucosal layer consists of connective tissue similar to that found in the lamina propria. Serous or mucous glands were not observed. The predominant characteristic in the adventitia is the presence of an incomplete hyaline cartilage ring, in the form of a circle. Dense connective tissue fills the space between the extremities of each cartilage ring. Serotonin-immunoreactive cells frequently had an apical cytoplasmic process directed towards the lumen, and were therefore classified as open type. The α-actin immunohistochemistry revealed smooth muscle cells only in blood vessel walls, confirming the absence of a tracheal muscle.