So the wall of the alveolus is lined with the polar fluid that contains a high surface tension. This means that because of the high surface tension, we require a relatively high pressure to expand and inflate those balloon like structures when we basically inhale our air. Now, by mixing the surfactant into that fluid, and by the way, the surfactant is produced by specialized type of cell inside the lungs known as the alveolar type two cells. By mixing the surfactant, which is our detergent with the fluid, we decrease the surface tension as a result of what we discussed earlier. And by decreasing the surface tension, we make it much easier for ourselves to actually inflate those alveoli. So we decrease the pressure that is needed to expand the alveoli during the process of inhalation.