:t ¡*r'S Ë'10'+ THE SUBMICROSCOPIC STRUCTURE OF THE DOLPHIN LUNG Joseph Charles Fanning M.B. , B.s. Department of Pathology UniyersitY of Adelaide A thesis presented for the Degree of Doctor of Philosophy May 1977 TABLE OF CONTEÀTTS I Introduction I II Ttre sramalian respiratory system 6 TII Ítre dolphin respiratory systeut 35 IV t"laterials and, mettrod.s 48 v Results 58 VI Discussion 94 vrr Overview 134 Appendix I 135 Appendix 2 1s5 Atr¡pendix 3 L78 BiJcliography L82 ST'M¡,IARY lftris thesis presenÈ the first detailed account of the submicroscopic sÈructure of the bronchial tree and lungs of a dolpt,jrn, Tursiops tm¿ncatus. The dolphin respiratory system is the most highly modified from the usual mammalian paÈtern of alt the ma¡runals. I consider, however, that the modifications are within the expressive range exhibited by marunalian lungs. Further, they are particularly suited to the marine existence of the dolphin. The trachea is short but wide. It is completely surrounded by anastomosing plates of hyaline cartilage embedded in a fibro- elastic membrane. fhree tlpes of epithelium line the trachea: (a) proxi-rnaliy there is a transitional tlpe which has an asyrûnetric unit membrane on its surface cells. This epithelium is similar to the transitional epithelium of the urinary bladder; (b) most of the trachea is lined by a stratified col,umnar epithelium wíth micro- villous surface cells, but no cilia. Proximally the asynunetric unit membrane extends into the surface ceIls, but disÈally these cells have a clear apical zone, a mitochondrial zone and a supra- nuclear organelle zone. This epithelium looks very like gallbladder epiÈhelium; (c) the distal parts of the trachea and the bronchi are lined by tlpical respiratory epithelium rdith cilia and goblet celIs. On the ventral aspect of the larlmgo-tracheal junction there are tonsil-like lymphatíc collections. Throughout the sr:bmucosa there are abundant rnucous and serous glands with ducts opening onto the surface. A rich vascular plexus and, a d.ense internal elastic lamina complete the submucosa. The air-conditioning of the inspired air is performed, in the trachea because of the modifications in the blowhole a¡rd nasal cavities. This means that the epithelium of the proximal trachea is sr:bjected to the particte load carried by the air, resulting in an increase at these leve}s. Protection of the ai::way is provided by the transitíonal epithelium, ttre flow of secretions from the glands and the tonsil- like ll'mphaÈic collections in the most dependent parts. Clearance of the trachea, in the absence of cilia is by gravity and mucous flow towards the lar1mx. The excess mucus and secretions are removed during the explosive expiratory phase of Èhe "b}o\r" . In addition ' the trachea must warm and hr:midify the inspired air a¡rd conserve water from the expired air. The venous plexus and the secretions from the glands assist with the former, while the microvillous epithelium Perfot:ns the latter function. Cartilage is present in the ainrays to their ternrination in the alveolar ducts. A system of myo-elastic sphincters in the terminal ai:*rays controls the flow out of the alveoli during the apneustic phase of respiration and diving. In this segment of the airway there is also an extensive capillary plexus covered only by squ¿rmous epithelial cetls. I have called this the respiratory bronchus. lltre alveolar septum has a thick connective tissue core $tith a capillary plexus on each surface. The alveoli are lined by tlpical tlpe I and tlpe II cells. Macrophages are frequently seen on the surface. The blood-air barrier is reduced to 200 nm in many areas. During diving the alveoli collapse due to the increasing hydro- static pressure and air is forced into the bronchial tree. The alveolar septr:rn folds in the gaps between the capillaries on complimentary surfêcês¡ thus maintaining the absorptive surface. It has been shown that dolphins use up to 958 of the inspired oxygen. I consider that the reduction in thickness of the blood-air barrier, a¡rd the double capillary plexus are responsible. The main fu¡rction of the respiratory bronchus is to remove the excess nitrogen which is absorbed by a counter-current flow, thus reducing the risk of the "bends" developing after a dive to shallow depths. Statement. ilt¡is thesis contains no material which has been accepted for the award of any other d,egree of diploma in any r¡niversity. 1o the best of ny knowledge and belief, this thesis contaíns no material previously published or written by another person, except when due reference is nade in the text of the thesis. Joseph C. Fanning. Acknowledgements. The work presented in this thesis was performed during my service in the Department of Anatomy, university of eueensland., from 1966 to 1968, and since 1969 in the Department of Pathology, University of Adelaide. Part of the writing ri¡as d,one during my study leave in the Department of Pathology, University of l{ashington, Seattle, U.S.A.. f am grateful for the assistance and advice given to me by merrbers of the staff of all three institutions, and particularly to the library staff for Iocating and obtaining sorne of the references. the animals used in the investigation were captured, und.er licence from the South Australian Government, by the staff of Marineland, of South Australia. I am grateful for their unselfish assistance, and expertise. !{r. D.Phillips, Miss L.Smart and Mrs. C.Lang assisted with the preparation of the electron microscopic specimens, while Mr. D.Caville assisted with the preparation of the final plates used. I am indebÈed to them for their excellent technical assistance. I will always be indebted to Professor H.W.!{hitting who introduced me to these remarkable animals. Professor R.J.Harrison, of canbridge university, has been my colla-bor- ator and adviser throughout Èhis investigation. r cannot thank him enough for what he has done. r hope that compleÈion of this thesis will in part repay that debt. Professor J.s.Robertson, my supervisor, has shown great und,erstanding and patience while this investigation, mainry AnaÈomicar, has been performed in his Pathology Department. r will always be grateful for his assistance and advice. To the many Cetologists throughout the world who have allowed me to exa.mine their specimens during the final stages I am grateful. To San Ridgway, Tag Gornwall, Bill Schevill and Gerry Kooymafi who very graciously discussed many aspects of the results in informal meetings. To my tlpist, t"larijke Genet, $rho converted my manuscript into its final form go my special thanks. The National Health and Medical Research Council of Australia provided a grant in aid from 1970 to L974. To my wife Anne, and my children withouÈ whose patience and understanding it would not have been possible to complete this work. 't ALL e?eatuîes thwt haue a bLouhoLe respír'e and ínspíre, fot, they ane prouíded tLth Lungs " Az,LstotLe. I. INTRODUCTION tì ALL Land anímaLs breathe, qrtd etten some uater animaLs, sueh as the uVnLe, the doLphin and aLL- the spouting Cetaeea tl ArLstotle Dolphins are air-breathing mammals which spend their entire life in the water. They are members of the order Cetacea, or whales and belong to the Odotocete, or toothed whale family. Dolphins range in size from the harbour porpoise, less than two metres in length' to the killer wha1e, up Èo nine metres in length. They are found in oceans and coastal waters around the world and even far inl-and in the great rivers of Asia, India and Souttt America. Dolphins and whales have had a special place in the minds of man for thousands of years. lltrey aPPear 'in some of the earliest rock carvings; in many myths and legends of coastal dwellers Èhroughout the worldr and in numerous passages in the bible and other religious writings (Slijper L962, 1976¡ Alpers 1963; Matthews 1968; Mclntyre L974). fhere has been increasinçt concern for the biology and conservation of all animals over Èhe last thirty years, and the dolphin has featured prominently in this. This concern has arisen in the case of the dolphin because: Èhe threat of extinction of the great whales by the commercial fishery of some nationst the inadvertent slaughter of large numbers of dolphins in the commercial tuna fishery in the Eastern Pacific Ocean; the rapid increase in the number of marinelands, aquaria and zoos using these animals for display purposest 2 a¡rd the suggestion that dolphins may be intelligent beings and the subsequent fear that man may exploit this to his own ends (evil or otherwise). Much of this has an emotional bias associated, with the priuritive beliefs mentioned above. (See Mclntyre I974i Lilly 1975¡ Greenwood 1976) The early writers in the field of Cetologry appear to have ignored Aristotle's description of tt¡e dolphin as a manmal and called them fish. It was only during ttre last century that dolphins and whales were generally accepted as air-breathing mammals (see Matthews 1968 and Harrison 1972 for a review of the controversy). Dolphins are playfut inquisitive creatures in their native envirorunent' and are often seen cavorting in small grouPs close to the beach. Often all that is seen is a dorsal fin arching out of the water. When one looks at the external features of the dolphin it is not surprising that they t{ere considered for many years to be'fish. .Do1phins have a streamlined fusiform body tapering from the thoracic region to the base of the tail. The vertebral column extends dístally almost to the base of the tail, but proximally a true neck ís not present and there is shortening and fusion of vertebrae.