Surface Lining of Lung Alveoli as a Structure

Abstract

HIGHLY surface-active material has been obtained from lung alveoli in the form of bubbles¹. The inference that extracts of mammalian lungs contain this material rests on the evidence that these extracts reduce surface tension at air–water interfaces on compression². Wide hysteresis loops, indicating an endergonic process with large changes in surface tension, are obtained in such experiments when surface tension is plotted against area of the film during a slow compression–expansion cycle. This behaviour has been used to suggest that surfactant in lung alveoli confers stability on lung tissue². This surface-active material has been cited also as a possible agent in the clearance of foreign material from lung alveoli and as a mediator in the exchange of respiratory gases³. It has been suggested earlier that this material possesses the physico-chemical attributes of cell membranes in general and, when cast off from the surface of air sacs, it fulfils its vital function in the lung due to its intra-alveolar spatial position^3,4. An attempt is made here to relate surfactant from lung alveoli to the basic ‘unit membrane’ of animal and plant cells⁵.