What is the primary function of the fetal lungs in a full-term fetus?

The primary function of the fetal lungs in a full-term fetus is associated with the production of amniotic fluid. During fetal development, the lungs are responsible for a process known as "lung liquid production," which contributes to the creation of amniotic fluid. This fluid is vital for the development of the fetus, facilitating movement and allowing the lungs to grow and develop properly. Although the lungs do not perform gas exchange in the same way postnatally due to the maternal circulation, their role in maintaining amniotic fluid levels is crucial for the overall well-being of the fetus before birth.

In the context of the other options, gas exchange and oxygenation of the blood are functions that the lungs will perform after birth, when air enters the lungs and the newborn begins to breathe independently. The filtering of toxins from the blood is primarily managed by the liver, not the lungs. Thus, recognizing the role of the fetal lungs in amniotic fluid production highlights their developmental importance before the fetus transitions to breathing air at birth.