Scanning electron microscope study of the morphology of the reptilian lung: The savanna monitor lizard varanus exanthematicus and the pancake tortoise malacochersus tornieri

Abstract

The morphology of the lungs of two reptilian species, Varanus exanthematicus and Malacochersus tornieri, have been studied on gross preparations, latex casts, and critical-point-dried tissues. The shape of these lungs was observed to conform with that of the body, the lung of the monitor lizard (Varanus) being long and ovoid while that of the pancake tortoise (Malacochersus) was rounded and laterally indented. With respect to the size distribution of the gas exchange compartments, the lungs were observed to be notably heterogenous. In both species these units were generally smaller in diameter in the cranial region of the lung while those in the caudal region were larger. The gas exchange compartments in the tortoise were more profusely compartmented with the primary, secondary, and tertiary septa being well developed while in the lizard only the primary and secondary septa were observed. The tertiary septa in the tortoise lung and the secondary septa in that of the monitor lizard defined the terminal gas exchange units, the faveoli. The cast impressions closely resembled the actual lung tissue and convincingly revealed the hierarchical design of the gas exchange compartments as they radiate from the air chambers and ducts, terminally giving rise to the faveoli. This stratification clearly increases the surface area available for gas exchange in these lungs. Disparate refinements of the basic reptilian lung design, as noted here, may lead to differing anatomic pulmonary diffusing capacities for oxygen to which characteristics like energetics and mode of respiration in this taxon may be attributed.

Developmental dynamics of the bronchial (airway) and air sac systems of the avian respiratory system from day�3 to day 26 of life: a scanning electron microscopic study of the domestic fowl, Gallus gallus variant domesticus

“…Day 18 these instructive sentiments are still quite legitimate. The marked difference between the design of the faveolar lung of reptiles (Maina et al 1989b, 1999, Perry 1989Maina 1990), a taxon from which birds arose (Pough et al 1989), and the parabronchial lung (Maina 2002a(Maina , 2002b attests to the fact that the evolution of the avian respiratory system wasn't a fortuitous event but rather a directed, highly innovative adaptive process.…”

Unidirectional pulmonary airflow patterns in the savannah monitor lizard

“…their length 21 . The primary bronchus runs the length of the lung, ballooning into a large sac-like bronchus just distal to the ostium of the caudal-most lateral bronchus ( Fig.…”

“…1b; Ssb). The respiratory parenchyma is largely restricted to the central and craniodorsal regions of the lung, with the saccular regions positioned at the cranial tip and caudoventral areas 21 . Small tertiary bronchi extend towards the pleural surface, forming hexagonal faveolar parenchyma 11,21 .…”

The Anatomical Record is Alive With Leapin' Lizards and Slitherin' Snakes

“…One of the Journal's Associate Editors J. P. Timmermans is co‐author of one of the papers on tongue, specifically tongue flicking in agamid lizards (Herrel et al, ). Near and dear to our hearts are two papers on the lung (Maina et al, ) and its surfactant system (Wetzstein et al, ).…”