Fig. 2

Histological characterization and histomorphometry data of the rabbit’s normal lung development. Representative microphotographs of the lung parenchyma during the pseudoglandular (A–C), canalicular (D–F), saccular (G–I) and alveolar phases (J–O) of lung development. The first two columns from the left, show sections stained with hematoxylin and eosin obtained at each lung developmental stage. In the right column, Masson’s trichrome staining (C) shows the scarce presence of intercellular matrix during the pseudoglandular phase, and orcein staining (F, I, L, O) shows fine elastic fibers (dotted arrows). The evolution of tissue density (TD), radial alveolar count (RAC) and the medial thickness of pre- and intra-acinar arteries (MT%) are shown in P, Q and R (as mean ± standard error of the mean of at least six lungs per phase of lung development. Asterisks above horizontal lines indicate a significant difference in the comparisons between different lung developmental phases (ANOVA followed by Tukey’s test; *P < 0.05; **P < 0.01; ***P < 0.001)