2 also called pulmonary surfactant. one of certain lipoproteins that reduce the surface tension of pulmonary fluids, allowing the exchange of gases in the alveoli of the lungs and contributing to the elasticity of pulmonary tissue.or example, if a drop of detergent is added to a drop of water, the detergent reduces the surface tension and the drop of water flattens out. In the lungs, surfactant reduces the surface tension and helps to maximize the surface area available for gas exchange.
The First Day of Summer 2016 (Summer Solstice) is on Monday, June 20. The First Day of Summer 2017 (Summer Solstice) is on Wednesday, June 21. The First Day of Summer 2018 (Summer Solstice) is on Thursday, June 21. The First Day of Summer 2019 (Summer Solstice) is on Friday, June 21. The First Day of Summer 2020 (Summer Solstice) is on Saturday, June 20.
This year, the last day of summer is Sept. 22. Photo: GETTY IMAGES. Labor Day marks the ceremonial end of summer, but there are still a good few weeks to enjoy the season, even after the three-day weekend ends and schools begin their calendar year. This year, the last day of summer is officially on Sept. 22. The fall equinox arrives Sept. 23 and so does the onset of shorter days in the Northern Hemisphere. Equinox is derived from the Latin words aequus, which means equal, and nox, the word for night.