surfactant /sərfak″tənt/ [L, superficies] , 1. an agent, such as soap or detergent, dissolved in water to reduce its surface tension or the tension at the interface between the water and another liquid. 2. 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. Also called pulmonary surfactant. See also alveolus, atelectasis, surface tension.
