The respiratory needs of the foetus are provided by the mother.
The foetal lungs produces amniotic fluid and a material known as surfactant and this reduces the surface tension of the fluids that line the bronchioles and alveoli. Surfactant is essential, because it clears the lungs of liquid. This enables the lungs to fill with air, so that the baby can begin breathing immediately after it has been born. As the baby takes its first breath, a number of respiratory and circulatory changes commence. These changes are essential, otherwise the baby could not live outside of its mother’s womb.
Surfactant production continues after birth, as it maintains the mechanical stability of alveoli and in so doing, prevents their collapse. If a baby does not have a sufficient amount of surfactant, it can result in respiratory distress syndrome (RDS), which causes increasing breathing difficulty for the baby. Insufficient surfactant is also a factor in adult lung disease.