[Physiology and physiopathology in the development and maturation of the antenatal lung]

Abstract

The term "pulmonary maturation" is reserved for the process of surfactant production. The term "pulmonary development" covers the overall phenomena of the growth of pulmonary structures and their differentiation. Pulmonary development is divided schematically into five stages: the embryonic stage up to the fifth to the seventh week of gestation, then the four stages of the foetal period. These four stages are: 1) The pseudo-glandular stage up to the seventeenth week during which the bronchi and the extra-acinar vessels are formed; 2) The canalicular stage characterised by the birth of the acinus, the differentiation of the cells and the beginning of surfactant synthesis to the end of this stage; 3) The saccular and alveolar stages. The saccular stage begins between the 24th and 26th week of gestation and at this stage the foetus is viable but exposed to the risk of neonatal respiratory distress on account of lack of surfactant. The alveoli are formed before the end of pregnancy. The factors controlling development and pulmonary maturation are still poorly understood. Cellular, particularly epithelial and mesenchymal interactions appear to play a major role in all the stages of development. Hormonal interactions play a determining role in pulmonary maturation. The effects on development and/or pulmonary maturation of pharmacological agents, hormones administered to the mother (e.g. opiates, glucocorticoids, aminophylline, beta-sympathomimetics, indomethacin and tobacco...) and maternal pathology are described as far as possible within the limits of our current knowledge. This information comes above all from experimental studies, thus the conclusions obtained are difficult to apply to newborn humans.