So these tiny molecules shown here are basically our surfactant molecules. So we have the non polar hydrophobic tail and the polar hydrophilic head. So in the same way that we discussed here, the head of the surfactant, the head of the surfactant basically interacts with the surface of our fluid, but the tail points away towards our air found within this cavity. 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.