Final answer:
Surfactant is a substance in the lungs that reduces surface tension in the alveoli, facilitates easier inflation of the airways, and prevents the collapse of alveoli, especially critical for newborns to breathe normally. It is comparable to a detergent that lowers the effort required to inflate a balloon.
Step-by-step explanation:
Surfactant is a substance that reduces the surface tension in the lungs, which is crucial for proper respiratory function. This detergent-like liquid is present in the airways and lines the alveoli, the tiny air sacs where gas exchange occurs. The primary role of surfactant is to decrease the work needed to inflate the airways and prevent the collapse of alveoli, especially during exhalation. It functions like a detergent that coats the interior of a balloon, making it easier to inflate. Surfactant is especially important in newborns, and insufficient levels can lead to respiratory distress syndrome in premature babies.The alveoli have a high surface tension due to the air-tissue/water interface, which would naturally cause them to collapse. Surfactant, comprised mainly of phospholipids and lipoproteins, effectively lowers this surface tension, ensuring that alveoli can easily expand and that smaller alveoli do not collapse, allowing for a stable gas exchange environment. In the context of lung mechanics, surfactant is important for both lung compliance (how elastic the lung is) and resistance (how much obstruction exists in the airways). Without sufficient surfactant, the lungs would require much more effort to breathe, akin to the resistance felt when blowing up an undeterred balloon. Thus, the correct answer to the question is c) Substance reducing surface tension in the lungs.