We have the cell labeled as number four. That is our alveolar cell type number two. And what this cell does is it produces and releases the pulmonary surfactant that is necessary to prevent the alveolis from actually collapsing when we exhale and to decrease the surface tension and therefore the pressure that is needed to actually inflate our alveolis. Now the cells shown by these green cells, number one. So if we zoom in on this small cross section, we get this blown up image. And so number one is our epithelial cells of the alveolus.