Abstract:
:Four species of Phocidae, or true seals, inhabit the waters surrounding the Antarctic continent. These animals are thought to have different diving capabilities. The Weddell seal, Leptonychotes weddelli, is known to be capable of attaining depths up to 600 meters. The respiratiory system of the Weddell seal shows the usual adaptations to an aquatic environment characteristic of other marine. These include lungs that undergo compression acollapse at depths greater than 70 meters; hyaline cartilage in the tracheo-bronchial tree as far as the terminal bronchioles; and large amounts of smooth muscle surrounding the distal-most bronchioles. The collapsible lungs provide a mechanism by which air is forced from the alveoli adjacent to the pulmonary capillary beds thereby preventing the absorption of nitrogen gas into the bloodsteam. The presence of hyaline cartilage throughout most of the tracheo-bronchial tree increases the effective dead air space that accommodates most of the air forced from the collapsed lungs. The smooth muscle surrounding the respiratory bronchioles prevents their collapse while under the pressures of a deep dive. Collapse of the respiratory bronchioles not supported by cartilage would trap air in the lung alveoli during a dive. In addition, large- sac-like "diverticulae" are found in the submucosa throughout the tracheo-bronchial tree. These diverticulae, which open directly into the lumen of the tree, appear to be modified glands whose cells, in most cases, do not appear to be specialized for secretory function. They are most numerous in the more distal bronchi and terminal bronchioles where they are situated on both the luminal and adventitial sides of the hyaline cartilage supporting the walls of the air passages. Diverticulae are not found in the respiratory bronchioles or in the respiratory portion of the lungs.
journal_name
J Morpholjournal_title
Journal of morphologyauthors
Boyd RBdoi
10.1002/jmor.1051470306keywords:
subject
Has Abstractpub_date
1975-11-01 00:00:00pages
309-36issue
3eissn
0362-2525issn
1097-4687journal_volume
147pub_type
杂志文章abstract::To date, the phylum Cycliophora comprises only one described extant species of acoelomate marine invertebrates, Symbion pandora. Adult specimens live commensally on the mouthparts of the Norwegian lobster, Nephrops norvegicus. Its complicated life cycle includes an asexually produced Pandora larva and a sexually produ...
journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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更新日期:1978-07-01 00:00:00
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journal_title:Journal of morphology
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更新日期:1995-04-01 00:00:00
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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更新日期:1988-05-01 00:00:00
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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更新日期:1978-05-01 00:00:00
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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journal_title:Journal of morphology
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更新日期:2017-07-01 00:00:00