In fetal lung development, which statement is true?

• A. Alveolarization is complete at 40 weeks gestation
• B. Lung volumes and surface area are determined strictly by gestational age
• C. Surfactant production is the sole determinant of lung maturity
• D. Gas exchange potential is determined by structural development of the lung (correct)

Answer: (D)

Gas exchange potential hinges on the physical maturation of the lung’s architecture, not just how many weeks a baby is in gestation or how much surfactant is present. For gas exchange to occur effectively after birth, the lung must develop a sufficient alveolar-capillary surface area with thin diffusion barriers—the alveolar-capillary membrane and the accompanying capillary network. Surfactant helps the lungs inflate and stay open, enabling ventilation, but without an adequate structural framework of alveoli, ducts, and capillaries, diffusion of oxygen into the blood (and removal of carbon dioxide) is limited.

Alveolarization continues after birth and varies with individual development, so lung volumes and surface area are not strictly determined by gestational age alone. The in-utero oxygen transfer occurs via the placenta, so the fetus relies on structural readiness to switch to pulmonary gas exchange after birth. The statement that best reflects this is that gas exchange potential is determined by the structural development of the lung.