THE ELEPHANTS RESPIRATORY SYSTEM - ADAPTATIONS TO GRAVITATIONAL STRESS

Elephants have had to adapt to gravitational stresses imposed on their very large respiratory structures. We describe some unusual features of the elephant's respiratory system and speculate on their functional significance. A distensible network of collagen fibers fills the pleu ral space, loosely connects lung to chest wall but appears not to cons train lung-chest wall movements. Myriad spaces within the network and its rich supply of capillaries suggest effective local sources and sin ks for pleural fluid that may replace the gravity-dependent flows of s maller mammals. The lung is partitioned into approximate to 1 cm(3) pa renchymal units by a system of thick, elastic septa that ramify throug hout the lung from origins on the lung's elastic external capsule. Par enchymal units suspended upon the elastic septal system protect depend ent alveoli from compression, thereby reducing the usual gravitational gradient of lung expansion. Intra-pulmonary airways are devoid of car tilage, instead they appear to derive resistance to collapse from teth ering forces of the attached septa. (C) 1997 Elsevier Science B.V.