[Non-ventilatory functions of the cells of the respiratory system].

The physiology of the respiratory system was limited until recently to study of the structures subjected to simple physical laws and involved in gas exchanges only. Today, the airways and lung itself are conceived as complex living structures adapted to defence against exogenous, microbiological, organic and inorganic substances which reach the respiratory epithelium, contained in the 10 to 12 m3 of air entering and leaving the lungs daily. In addition, the considerable surface area represented by the endothelium of the pulmonary circulation is a site of synthesis and elimination, the implications of which are increasingly important in the area of the metabolism of endogenous substances: prostaglandins, vasomotor substances and the bioconversion of drugs and toxic agents. This is an increasingly large area of research and investigation, the clinical applications of which appear to be more and more frequent and important.