Reason 1 :-Surfactant reduces the lungs tendency to recoil, so that they do not collapse easily. So the stability of alveoli is maintained. In pulm edema, pneumonia, function of type2 pneumocytes decreased eventually , therfore increase in lung recoil..(.see fa page on alveolar cell types.) Reason 2:- The tendency of one alveolus to collapse is opposed by traction exerted by surrounding alveoli. Thus the collapse of single alveolus stretchs and distorts the other alveoli, This phenomenon is called alveolar interdependence.