Scanning electron microscopic study of the microarchitecture of the lung of the giant salamander Amphiuma tridactylum.

This paper reports observations made using scanning electron microscopy (SEM) on the internal structure of the lung of Amphiuma tridactylum. This lung is highly septate at the cranial end, but the septa become gradually reduced in size and number with increasing distance caudally until the septa are reduced to ridges in the wall of the lung. However, there is no respiratory dead space as respiratory epithelium is found throughout the lung. Treatment of isolated lung segments with acetylcholine causes the septa to shorten and thicken which in turn causes the lung diameter to decrease and the alveoli to collapse. These observations are consistent with the hypothesis that the collapse of the Amphiuma lung in vivo, which is responsible for the highly efficient ventilation of the lungs, is brought about by the contraction of pulmonary smooth muscle in the septa and wall of the lung.