Histologia Descritiva do Esôfago de Juvenis de Podocnemis Unifilis (Troschel, 1848) (Testudines: Podocnemididae)

Abstract

The Amazon region is home to 17 species of chelonians, where the Podocnemididae family is relevant to local ecology and culture, acting in nutrient cycling and the subsistence of local communities. Among them, Podocnemis unifilis, widely distributed, which has an omnivorous feeding habit with a tendency towards herbivory. This research sought to investigate anatomical and histological aspects of the esophagus of P. unifilis, to collaborate with data on the species and its specific characteristics. In this study, five juvenile specimens of P. unifilis were collected from the Tocantins River, between the municipalities of Itapiratins and Tupiratins, through active collection (line and hook), transported to the Plant Anatomy and Histological Techniques laboratory (UFT- Campus Palmas), subjected to biometric and euthanasia protocols. The samples were fixed in 10% formaldehyde and stored in 70% alcohol for analysis under light microscopy, starting with dehydration of the esophageal samples, embedding in paraffin for microtomy at 4μm, adhering the sections to histological slides with Haupt's adhesive and formalin. Afterwards, the slides were stained with Hematoxylin and Eosin (HE) and Masson's Trichrome (TM). Furthermore, samples were analyzed using scanning electron microscopy, for comparison with analyzes using light microscopy. In the histological analysis, a mucous region was observed, consisting of stratified epithelium; a submucosa, formed by loose connective tissue, with adaptations such as projections of these, originating papillae and invaginations and forming longitudinal folds in the anterior portion of the organ, acting to expand the volume of the esophagus in order to accommodate different sizes of food. The observed anatomical and histological adaptations were reflections of its dietary appearance. The esophagus is anatomically tubular, composed of layers of mucosa (mucus and enzyme production), submucosa (enzyme production, support and nutrition) covered by smooth muscles. It is responsible for peristaltic movements that propel food towards the stomach. The mucous region has an irregular surface region with the presence of cracks, responsible for the release of mucus that lubricates and releases pre-digestive enzymes. It is concluded that the adaptations of the esophagus correspond to the dietary characteristics indicated for the species. Although, in the case of juvenile specimens, these adaptations can change throughout their development, as reported in the literature for similar species in the same genus. These data can collaborate with the identification and characterization of the species and management and conservation strategies for food aspects.