Development of the fetal and newborn lung--morphometric studies (rat model)

The aim of this study was to investigate the development of the fetal lung by morphometric means. Lung specimens from 16-20 day-old fetuses, and 1, 3, 5, 14 and 21 day-old newborns were used. Tissue specimens were evaluated by light microscopy and transmission electron microscopy. The material was divided into four groups--related to four main stages of lung development (pseudoglandular, tubular, saccular and alveolar). For each developmental stage, 30 photographs of semi-thin sections were saved on computer hard disk for future morphometric measurements. OPTIMAS 4.02 software was used for evaluation of the relative area occupied by vascular, epithelial, stromal and fluid/gaseous compartments. GraphPad InStat software was used for statistical analysis. All measurements and calculations were done per observation field. The area occupied by vessels was greatest at the pseudoglandular stage (11.7%), and smallest at alveolar stage (5.7%). The stroma also occupied the largest area at the pseudoglandular stage (58.4%) and the smallest at alveolar stage (17.0%). The area occupied by epithelial cells was most extensive at the tubular stage (52.5%) and smallest at the alveolar stage (6.1%). The fluid/gas compartment was largest at the alveolar stage (70.5%) and smallest at the pseudoglandular stage (0.58%). The present results indicate that the most dynamic lung development occurs during thin air-blood barrier formation (19th day of intrauterine life to 5th day after delivery--saccular and the beginning of alveolar stage).