Surface tension The surface tension at the air-water interfaces within the alveoli At an air-water interface Alveolar Sacs the attractive forces between the water Pulmonary Artery molecules(surface tension Alveoli make the alveoli like stretched balloons that constantly try to shrink and resist further stretching Bronchiole Pulmonary VeinSurface tension ◼ The surface tension at the air-water interfaces within the alveoli. ◼ At an air-water interface, the attractive forces between the water molecules (surface tension) make the alveoli like stretched balloons that constantly try to shrink and resist further stretching