Some diseases of this organ may cause the formation of spiral-shaped mucus casts called Curschmann's (-5[1])spirals. A common side effect of prolonged treatment with busulfan is interstitial fibrosis in this organ. Like the liver, this organ can be damaged by genetic deficiency of a serine peptidase inhibitor called alpha-1 antitrypsin. A tumor in the upper part of this organ can result in anhidrosis and ipsilateral ptosis (TOH-siss) in Horner's syndrome. An elevated CD4/CD8 ratio in a fluid collected from this organ can be indicative of sarcoidosis. This organ's function can (10[1])be plotted in flow-volume loops, which can help characterize obstructive and restrictive disorders in this (10[1]-5[1])organ. NRDS can be caused by the inability of newborns to produce (10[1])surfactants in this (10[2])organ. For 10 points, name this (10[1])organ that facilitates gas exchange during (10[1])breathing. (10[1])■END■