The structure and function of crocodilian lungs are unique compared with those of other reptiles. We examined the extent to which this and the semi-aquatic lifestyle of crocodilians affect their respiratory mechanics. We measured changes in intratracheal pressure in adult and juvenile caiman (Caiman yacare) during static and dynamic lung volume changes. The respiratory mechanics of juvenile caiman were additionally measured while the animals were floating in water and submerged at 30, 60 and 90 deg to the water's surface. The static compliance of the juvenile pulmonary system (2.89±0.22 ml cmH 2 O −1 100 g −1) was greater than that of adults (1.2±0.41 ml cmH 2 O −1 100 g −1), suggesting that the system stiffens as the body wall becomes more muscular and keratinized in adults. For both age groups, the lungs were much more compliant than the body wall, offering little resistance to air flow (15.35 and 4.25 ml cmH 2 O −1 100 g −1 for lungs, versus 3.39 and 1.67 ml cmH 2 O −1 100 g −1 for body wall, in juveniles and adults, respectively). Whole-system dynamic mechanics decreased with increasing ventilation frequency (f R), but was unaffected by changes in tidal volume (V T). The vast majority of the work of breathing was required to overcome elastic forces; however, work to overcome resistive forces increased proportionally with f R. Work of breathing was higher in juvenile caiman submerged in water at 90 deg because of an increase in work to overcome both elastic and flow resistive forces. The lowest power of breathing was found to occur at high f R and low V T for any given minute ventilation (V E) in caiman of all ages.
OLIVEIRA, P. R. C. de; PEDROSA, M. M. D. Fisiologia de extremos: digestão em répteis de alimentação esporádica. Arq. Ciênc. Vet. Zool. UNIPAR, Umuarama, v. 19, n. 3, p. 195-202, jul./set. 2016. RESUMO:Entre as diversas adaptações que os seres vivos apresentam em resposta às variáveis do ambiente, estão as mudanças adaptativas morfológicas e funcionais a curto e longo prazo que acontecem no sistema digestório em resposta ao padrão de alimentação. Em alguns répteis, tais adaptações vêm ao encontro da maximização dos recursos energéticos, os quais correlacionam os hábitos alimentares ao rendimento energético por meio do processo de regulação de órgãos específicos. Considerável número de artigos discute o desempenho do trato gastrointestinal e a influência de outros sistemas no auxílio a esse comportamento do sistema digestório em répteis, especialmente em pítons. Este trabalho teve por objetivo destacar e discutir as ações fisiológicas envolvidas no processo digestório e em outros sistemas em répteis que se alimentam esporadicamente. A atrofia e reconstrução alternadas do trato gastrointestinal em animais de hábitos alimentares infrequentes garantem a esses uma economia de energia em períodos de jejum e uma alta captação dos nutrientes no período digestivo. Essas alterações são acompanhadas por variações funcionais ácido-básicas, respiratórias e hemodinâmicas, e consequentemente por grandes mudanças na taxa metabólica, quando os estados de jejum e pós-prandial são comparados. PALAVRAS-CHAVE: Píton. Regulação visceral. Répteis. Respiração. Sistema digestório. EXTREME PHYSIOLOGY: DIGESTION IN INTERMITTENT-FEEDING REPTILESABSTRACT: Short-and long-term morphological and functional adaptive changes in the digestive system related to the feeding habits are among the many adaptations living beings have in response to environmental variables. In some reptiles, such adaptations aim at maximizing the energy resources, which correlate the feeding habits with the energy performance through the regulation of specific organs. A considerable number of articles address the performance of the digestive tract and the influence of other systems in helping this digestive system behavior in reptiles, especially pythons. This paper has the purpose of highlighting and discussing the physiological actions involved in the digestive process and in other systems in reptiles that feed sporadically. The alternate atrophy and reconstruction of the gastrointestinal system in infrequentfeeding animals allow them to save energy during fasting and a high uptake of nutrients during digestion. These changes are accompanied by acid-base, respiratory and hemodynamic alterations, and therefore, by large changes in the metabolic rate, when comparing fasting and the post-prandial periods. KEYWORDS: Digestive system. Reptiles. Respiration. Visceral regulation. FISIOLOGÍA DE EXTREMOS: DIGESTIÓN EN REPTILES DE ALIMENTACIÓN ESPORÁDICA RESUMEN:Entre las diversas adaptaciones que los seres vivos tienen, en respuesta a las variables ambientales, están los cambio...
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