In RDS which is damaged?
In ARDS, alveolar capillary endothelial cells & type 1 pneumocytes(alveolar epithelial cells) are damaged/injured, leading to the loss of the normally tight alveolar barrier to fluid and macromolecules. 
As a result, oedema fluid rich in protein accumulates in the interstitial & alveolar spaces. Condensed plasma proteins aggregate in the air spaces with cellular debris and dysfunctional pulmonary surfactant to form hyaline membrane whirls.
Type 2 pneumocytes
Type 1 pneumocytes
Clara cells
Clara cells