Morphological characteristics of the lungs from cetaceans stranded in the Canary islands

Abstract

Introduction: Marine mammals present numerous morphophysiological adaptations for surviving in the marine environment. Of all evolutionary adaptations, the lungs set apart from the rest. This is one of the main anatomical differences respect to land mammals. In marine mammals, pulmonary viscera size has not changed so much, but there is an increasing about the number of pulmonary alveoli which represents a highest speed in the gaseous exchange. Materials and method: Different cetacean species beached in Canary Islands were used for this study. We took photos of the different anatomical parts of the respiratory system during this necropsy. Later, clinically relevant thoracic anatomical structures were identified using different anatomical and physiological papers and books. Results: Macroscopically, lungs were covered by thin and stretch pleura which together with the myoelastic fibers of the parenchyma provided some elasticity characteristics to the organ. The shape of the lungs was frequently prismatic with the edges more emphasized than terrestrial mammals. No lobes were observed, only a less accentuated cardiac notch at level of left lung. It was characteristic in all cetacean species observed, a higher number of lymphatic structures surrounding all the ventral edge until converging to the basal edge. These structures were among the sheets of pulmonary pleura. Furthermore, there were big size lymph nodes on the vertebral portion of the medial face. About bronchial tree distribution, for ventilating the right cranial lobe existed a tracheal bronchus and two short main bronchi. Esophageal and cranial cava vein imprints were emphasized in the right lung medial face, as the aortic arch and thoracic aorta imprints in left lung. Discussion: Studies of marine mammal anatomy are very limited because of the difficult to find healthy specimens and the access to this kind of animals. The scarce bibliography makes reference about the physiology of the marine mammals related to the habitat, where the morphology of these animals is barely studied. It is worth highlighting, some studies about the relation of the pulmonary size and the ribcage morphology in cetaceans, and the macroscopical anatomy of the lower respiratory tract in Ringed Seal (Pusa hispida).