Gas exchange strategy in the Nile crocodile: a morphometric study |
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Authors: | S F Perry |
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Institution: | (1) Fachbereich 7 (Biologie), Universität Oldenburg, D-2900 Oldenburg, Federal Republic of Germany |
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Abstract: | Summary The respiratory surface area (SAR) per kilogram body mass (MB), the harmonic mean thickness of the air-blood barrier ( htR) in the gas exchange tissue, and the anatomical diffusion factor (ADF=SAR/ htR per MB) were calculated for four juvenile Nile crocodiles. The ADF of three small specimens (mean MB=3.59 kg) was 625 cm2· m–1·kg–1. The values varied considerably among individuals and were similar to that of a 5.68-kg specimen (593 cm2· m–1·kg–1). Only 9% of the ADF is located in the anterior third of the lung, which because of its conical shape makes up only 14 percent of the total lung volume. Particularly in the middle third of the lung, the proximal region near the intrapulmonary bronchus displays a greater ratio of respiratory/non-respiratory surface areas than do more distally located sampling sites. The htR is also significantly smaller proximally than distally. The cumulative ADF per unit MB is greater than that previously reported for this species on the basis of overall estimates of SAR and htR, but is still less than that of lizards and testudinids. The disposition of ADF between distal air storage region and the intrapulmonary bronchus is consistent with a bidirectional cross-current gas exchange model.Abbreviations
ADF
anatomical diffusion factor
- %AR
percent of SA included in the effective respiratory zone
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M
B
body mass
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NVP
non-ventilatory period
- %P
percent of total lung volume containing parenchyma
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S
A
total surface area of intrapulmonary septa
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S
ANR
that portion ofS
A
lying out the effective respiratory zone
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S
V
surface-to-volume ratio in the parenchyma
- htR
harmonic mean thickness of the air-blood tissue barrier within the respiratory zone
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V
P
parenchymal volume
-
VP
ventilatory period |
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Keywords: | Crocodile Lung Morphometry Strategy Evolution |
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