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Observations on the anatomy of the respiratory system of the river otter, sea otter, and harp seal. II. The trachea and bronchial tree

Canadian Science Publishing
Canadian Journal of Zoology
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The trachea of the river otter and sea otter are morphologically similar to each other, whereas the trachea of the harp seal is relatively shorter and broader and has noncalcified overlapping cartilaginous rings and a relatively thicker lamina propria. The harp seal has fewer cartilaginous rings, the arms of which overlap dorsally in the cranial two-thirds of the trachea. The bronchial blanching patterns are similar in the river otter and sea otter, with the pennate-like branching of the lobar bronchi corresponding to the lobes of the lungs. In the harp seal there are more dichotomous branchings of the lobar bronchi, with close symmetry between the right and left lungs. Bronchiograms and dissections indicate that the numbers of subsegmental bronchioles increase from the river otter to sea otter to harp seal.
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... The present study focused on the South American fur seal or Arctocephalus australis, an otariid included in the taxonomic family of pinnipeds (Order Carnivora), such as the dog or the cat [6,7]. Surprisingly, although it is generally accepted that anatomy is crucial to a better understanding of different physiological adaptations [2], and although studies on the physiology of diving are numerous [1,[8][9][10][11][12][13][14][15][16][17][18][19], only a small number of them analyze the anatomical characteristics of marine mammals [5,[20][21][22][23][24], and even fewer are focused on the anatomy of the respiratory system [2,3,[25][26][27]. ...
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... They do not need rapid ventilation, as is the case in cetaceans, and neither live constantly on land. This could also be the reason why the Arctocephalus australis has a short trachea and long bronchi, especially when compared to land mammals, whose ventilation demands are different [25]. ...
Article
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Article
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In this Review, we focus on the functional properties of the respiratory system of pinnipeds and cetaceans, and briefly summarize the underlying anatomy; in doing so, we provide an overview of what is currently known about their respiratory physiology and mechanics. While exposure to high pressure is a common challenge among breath-hold divers, there is a large variation in respiratory anatomy, function and capacity between species textendash how are these traits adapted to allow the animals to withstand the physiological challenges faced during dives? The ultra-deep diving feats of some marine mammals defy our current understanding of respiratory physiology and lung mechanics. These animals cope daily with lung compression, alveolar collapse, transient hyperoxia and extreme hypoxia. By improving our understanding of respiratory physiology under these conditions, we will be better able to define the physiological constraints imposed on these animals, and how these limitations may affect the survival of marine mammals in a changing environment. Many of the respiratory traits to survive exposure to an extreme environment may inspire novel treatments for a variety of respiratory problems in humans.
... Descriptions of the internal anatomy of river otters from Oklahoma are few. The length of river otter trachea has been described as intermediate between that of terrestrial carnivores and marine mammals and a shorter trachea facilitates air exchange and increases lung ventilation in diving mammals (Tarasoff and Kooyman, 1973b). The mean tracheal length of river otters is reported as 15.3 cm, or 23.2% of the body length (Tarasoff and Kooyman, 1973b;Lariviere and Walton, 1998). ...
... The length of river otter trachea has been described as intermediate between that of terrestrial carnivores and marine mammals and a shorter trachea facilitates air exchange and increases lung ventilation in diving mammals (Tarasoff and Kooyman, 1973b). The mean tracheal length of river otters is reported as 15.3 cm, or 23.2% of the body length (Tarasoff and Kooyman, 1973b;Lariviere and Walton, 1998). However, the length of trachea in this river otter was 21.1 cm (measured from the top of the forking of the branching of the bronchi to the rim of the trachea below the bottom of epiglottis). ...
... However, the vocal anatomy of the Weddell seal is not yet well known. Based on an average trachea length of 17.6% of the total body length observed in harp seals (Tarasoff & Kooyman, 1973), the current best estimate that can be made of the likely length of a Weddell seal trachea is~44-51 cm (based on estimated body length 2.5-2.9 m; Thomas & Terhune, 2009). The estimated length of the resonating chamber associated with the lower frequency peak falls in a similar range to this expected trachea length. ...
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During the breeding season, male Weddell seals (Leptonychotes weddellii) defend underwater territories using high amplitude trill vocalizations (some >190 dB re 1 μPa‐m). The source‐filter theory states that the characteristics of vocalizations are a product of both the sound produced at the source and the effects of soundwave reflection within the vocal tract. This study aimed to determine the relative influence of reflection (resonance). Weddell seal trills (tonal descending frequency sweeps ranging from >20 to <0.1 kHz) offered a unique opportunity to look for resonance in the spectral patterns, appearing as periodic peaks in amplitude over short frequency intervals. Additionally, distributions of frequencies with absolute maximum amplitude (FMA) were tested against random distributions to look for frequencies where FMAs occur more frequently than by chance. All methods exhibited evidence of resonance at 0.45–0.56 and 2.25–2.83 kHz. These frequencies would resonate in closed‐at‐both‐ends tubes with lengths of 32–40 and 6–8 cm, respectively. These lengths approximate the likely sizes of the trachea and larynx or pharynx respectively. The amplitudes of the underwater calls of Weddell seals primarily result from the amplitude generated by the sound source in the larynx with some additional amplitude associated with resonance in the vocal tract.
... Calcification/ ossification of the more cranial parts of the trachea and larynx also occurred in subadults but the author could not attribute this to any specific behavior. In mammals, for example, LRT ring calcification is observed in shallow diving sea (Enhydras lutris) and river (Lutra canadensis) otters (Tarasoff & Kooyman, 1973). Although these mammals do not dive to great depths like some other mammalian taxa, they do experience increased pressure on their bodies upon descent. ...
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The production of echolocation calls in bats along with forces produced by contraction of thoracic musculature used in flight presumably puts relatively high mechanical loads on the lower respiratory tract (LRT). Thus, there are likely adaptations to prevent collapse or distortion of the bronchial tree and trachea during flight in echolocating bats. By clearing and staining (Alcian blue and Alizarin red) LRTs removed from nonvolant neonates, semivolant juveniles, volant subadults, and adult Jamaican fruit bats (Artibeus jamaicensis), I found that calcification of the tracheal, primary bronchial, and secondary bronchial (lobar) cartilage rings occurs over the span of about 3 days and coincides with later developmental stages of flight and the increased production of echolocation calls. Tracheal rings that are immediately adjacent to the larynx calcified first, followed by more caudal tracheal rings and then the rings of the primary and secondary bronchi. I suggest that calcification of LRT cartilage rings in echolocating bats provides increased rigidity to counter the thoracic compressions incurred during flight. Calcification of the LRT rings is an adaptation to support the emission of laryngeally produced echolocation calls during flight in bats.
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Book
Berta and Sumich have succeeded yet again in creating superior marine reading! This book is a succinct yet comprehensive text devoted to the systematics, evolution, morphology, ecology, physiology, and behavior of marine mammals. The first edition, considered the leading text in the field, is required reading for all marine biologists concerned with marine mammals. Revisions include updates of citations, expansion of nearly every chapter and full color photographs. This title continues the tradition by fully expanding and updating nearly all chapters.
Chapter
This chapter explores some basic patterns that are seen among marine mammals with respect to diving. The details of diving behavior are often difficult to observe and interpret, for they usually occur well below the sea surface. Measured as either the maximal achieved depth or the maximal duration of a dive, the diving capabilities of marine mammals vary immensely. Some species of marine mammals are little better than the best human free-divers, whereas some whales and pinnipeds are capable of astounding feats that include diving for periods of hours to depths of kilometers. The effects of pressure on the diving animal involve circulatory and respiratory adaptations. Among circulatory changes—in pinnipeds and cetaceans—are enlargement and increased complexity of blood vessels, including the development of retia mirabilia throughout the body, which serve as oxygen reservoirs during deep dives. The muscles, blood, and spleen are important for oxygen stores in marine mammals. Respiratory adjustments that occur during diving involve modifications in the structure of the lungs, especially the bronchioles. It is suggested that the walrus is capable of deep dives but has little reason to do so because of the availability of its prey in shallow water. Considerably, smaller phocid seals exceed the diving and breath-holding capacities of most whales. Possible explanations for this include less accurate measurements of cetacean diving behavior and their exploitation of prey located at shallower depths.
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A captive pilot whale emptied as much as 88 percent of lung gas passively, without the aid of expiratory muscles. Level or decreasing pressures in the esophagus during expiration, and in the blowhole at the onset of expiration, revealed the driving force of expiration to be solely elastic recoil. Active muscular reexpansion of the lungs ensued immediately. Expiration and inspiration were completed in about I second.
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