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 to support amniotic fluid production. The fetal lungs play a key role in the production of lung fluid, which contributes to the volume of amniotic fluid surrounding the fetus. This fluid is crucial not only for protecting and cushioning the fetus but also for allowing for the normal development of the lungs and other organs.

While oxygen exchange is vital for newborns after birth, in the fetus, the placenta is responsible for this gas exchange, rendering the lungs non-functional in that capacity until birth. Fetal breathing movements serve to prepare the lungs for their role post-delivery but don't facilitate gas exchange before birth. Filtration of toxins is also primarily handled by the placenta and maternal circulation rather than the fetal lungs.

Thus, the production of amniotic fluid by the lungs is an essential function that aids in the overall health and development of the fetus while in utero.