Some figures from previous manuscripts showing some of the characteristics of an alveolus in normal vs idiopathic pulmonary fibrotic (IPF) lungs. Final version dos not illustrate the epithelial to mesenchymal transition (EMT) in favor of showing greater susceptibility of IPF patients to environmental pollutants such as bacteria and particulates. Final version is published in Evans CM, et al, Physiol Rev 96(4):1567-91 (https://www.physiology.org/doi/abs/10.1152/physrev.00004.2016). Made it on the cover of the same issue. Free for the public to read.