Terminal airway and alveolus Type I Unit of gas exchange epithelium Type I the ultimate site of gas exchange ALVEOLUS ALVEOLAR respiratory bronchioles, alveolar ducts, SPACE alveolar sac alveoli ° Alveolar type I cell 95% of the surface CAPILLARY gas permeable LUMEN ° Alveolar type ll cell 5% of the surface Type Il producing surfactant, lowering the surface tension, Endothelium involved in the re pair of alveolar epithelium Interstitial cell Endothelium 55 Terminal airway and alveolus • Unit of gas exchange the ultimate site of gas exchange — respiratory bronchioles, alveolar ducts, alveolar sac, alveoli • Alveolar type I cell — 95% of the surface — gas permeable • Alveolar type II cell — 5% of the surface — producing surfactant, lowering the surface tension, involved in the repair of alveolar epithelium