Final answer:
A surfactant is a substance made by the lungs, composed of phospholipids and lipoproteins, that reduces the surface tension of water in the alveoli to prevent their collapse and facilitate breathing.
Step-by-step explanation:
A surfactant is a substance made by the lungs to help reduce the surface tension of water in the alveoli. The presence of surfactant is crucial for proper lung function, as it lowers the surface tension at the air-water interface within the alveoli, facilitating their expansion during inhalation and preventing collapse during exhalation. This surfactant is a mixed composition of phospholipids and lipoproteins.
The high surface tension of the alveoli can otherwise lead to difficulties in the inflation of the alveoli and potential collapse, making breathing more laborious, especially in the newly born, where surfactant production may be insufficient. The action of surfactant in reducing surface tension is akin to the ways detergents work by creating conditions that make it easier to overcome the cohesive forces of liquid molecules.
However, unlike common detergents, pulmonary surfactants have unique properties that help maintain the stability of small alveoli and prevent overexpansion of large ones, hence maintaining optimal gas exchange.