Respiratory System of the Two-Toed Sloth (Choloepus didactylus): Macroscopic, Histological and Scanning Electron Microscopy Analysis

Relatively little research has been conducted regarding Choloepus didactylus and studies that have been done have mainly covered physiology and morphology, as well as studies on its respiratory system. The objective of this study was to describe the components of the respiratory system of the two-toed sloth and compare it with other species already described in the literature. For this purpose, eight adult animals were used. Macroscopic analyses were carried out on the organs that make up the respiratory system, which confirmed the existence of four cartilages of the larynx, trachea with an average of 37 incomplete tracheal cartilages and lung, highlighting the absence of the accessory pulmonary lobe being composed only of the right cranial and caudal, left cranial and caudal lobes. After the standard protocol, microscopic analyses of fragments of the organs evidenced in the macroscopic study were carried out, using optical microscopy and scanning electron microscopy, in addition to chest x-rays with positive contrast media through orotracheal intubation. Finally, we conclude that microscopically the respiratory system of the two-toed sloth is like other Xenarthra and some domestic animals. Macroscopically, the nose is like Choloepus hoffmanni, the nasal cavity to other species of Xenarthra already described in addition to domestic animals. The trachea differs from other species in terms of the number of tracheal rings and extension. As for the lungs, they were the ones that differed most when compared to other Xenarthra and to domestic animals as it was the species with the least lobation.