Placental Gas Exchange

Gas exchange in the placenta is much less efficient than in a lung. This is because the minimum diffusion distance is much larger (eg 3.5 μm vs 0.5 μm in the lung) and the permeability of the blood-blood barrier is much lower then the permeability of the blood-gas barrier in the lung.

The total surface area of the placenta at term is about 16 m2 as compared to 50 to 60 m2 in the adult lung. The surface area is about a quarter of the size but it transfers only one-tenth of the oxygen. The inefficiency of the gas exchange is compensated for by a relatively much larger surface area.

In summary, as compared to the adult lung, the placenta is inefficient at gas exchange because of larger diffusion distance and lower gas permeability.

Category: Obstetrics Notes