1. Highly vascularised/supplied with numerous capillaries;to remove respiratory gases from the surface to avoid saturation
2. Moist ; to allow respiratory gases dissolve in solution form
3. Has highly folded alveoli with many air sacs; to increase surface area for gaseous exchange
4.Alveoli are thin; to reduce diffusion distance hence faster diffusion of respiratory gases
5.Elastic/Spongy; to allow accomodation of large volume of gases
6. ventilated/connected outside/supplied with bronchi ; to avail gases for exchange