Histologic appearance and morphometric quantification of lung structure in preterm lambs supported by NIS, with or without restricted nutrition (RN). Panels a and b: NIS control lung. Panels c and d: NIS+RN lung. TRU = terminal respiratory unit, DAS = distal airspace, A = alveolus. * identifies the enlarged region in panels b and d. Lung parenchyma of the NIS control group has thinner distal airspace walls (arrow), and more and thinner alveolar secondary septa (arrowhead) compared to corresponding NIS+RN group (panels a and c, the scale bar is 20 μm; panels b and d, the scare bar is 100 μm). Images are representative of the morphometric results shown in panel e, f, and g. Morphometric results are shown as mean ± SD for n=4/group. White fill indicates NIS control; black fill indicates NIS+RN. Radial alveolar count (panel e) and volume density of secondary septa (panel f) are significantly greater in the NIS control group compared to the NIS+RN group. Distal airspace wall thickness (panel g) is significantly less in the NIS control group compared to the NIS+RN group. *Different from the NIS control group by Mann-Whitney U test (p < 0.05).