The alveoli are normally kept dry by the:-

Surfactant is a mixture of dipalmitoyl phosphatidyl choline, other proteins & lipids. Role in keeping alveoli dry :- 1. The lipids in the alveolus 2. In the absence of surfactant, the unopposed surface tension in the alveoli would produce a force that greatly ors transudation of fluid from blood into alveoli. Note Factors increasing surfactant synthesis: Factors decreasing surfactant synthesis: Glucocoicoids Thyroxine Stretching of lungs in infancy Beta adrenergic agonist Calcium Smoking Long term inhalation of 100% oxygen Occlusion of main bronchus/pulmonary aery