Final answer:
Surfactant is a substance that reduces the surface tension of alveolar fluids, preventing alveoli from collapsing and aiding efficient respiration.
Step-by-step explanation:
Surfactant is the substance secreted by cells of the alveoli that reduces the surface tension of the fluid around the alveoli, preventing their collapse. The high surface tension at the alveoli's air-tissue/water interface is counteracted by surfactant, which is a complex mixture of phospholipids and lipoproteins. These substances are particularly important for decreasing the tendency of alveoli to collapse upon exhalation.
The role of surfactant is crucial during the respiratory cycle. During inhalation, surfactant molecules are pulled apart, increasing wall tension as the radius of the alveoli increases. Conversely, during exhalation, these molecules slide back together, decreasing the surface tension and helping to prevent alveolar collapse. This unique adjustment of wall tension helps maintain the stability of alveoli sizes during the breathing process.
In the absence of sufficient surfactant, such as in premature babies, respiratory distress syndrome can occur due to increased work needed to inflate the lungs. Therefore, the production and function of surfactant are essential for effective and efficient breathing and oxygen exchange within the alveoli.