In the lungs, surfactant is secreted by cells.

Surfactant, which is a mixture of fatty lipids and proteins are secreted by alveolar type II cells that line the perimeter of the inside of our empty alveolar space and aids in the movement of air and liquids that go in and out of the lungs. These cells may line other vital organs to protect it against outside wear and tear and keep the tissue inside our bodies intact making bodily functions working more smoothly.