What is surfactant and its function in the alveoli?

Surfactant is a substance produced in the alveoli, which are the tiny air sacs in the lungs where gas exchange occurs. Its primary function is to reduce surface tension at the air-liquid interface within the alveoli, thereby preventing alveolar collapse, especially during exhalation when the lung volume decreases. By lowering surface tension, surfactant ensures that the alveoli remain open and can easily expand and contract with each breath. This is crucial for maintaining proper lung function and efficient gas exchange, as collapsed alveoli would hinder the movement of oxygen into the bloodstream and carbon dioxide out. The production of surfactant begins late in fetal development, which is why it is essential for the lungs to be sufficiently mature before a newborn can breathe air effectively.