"Picture the lungs as an upside-down tree: the trachea is the trunk, the bronchi are the large branches, the bronchioles are the smaller branches, and the alveoli (air sacs) are the leaves. The branches and leaves are essential for breathing.

"Babies' lungs go through their final stages of development in the last few weeks before birth. When babies are born prematurely (before 36 weeks of gestation), this process is cut short.

"This illustration shows how the lungs of a premature baby differ from those of a full-term infant. The lungs of a full-term baby look like a full-grown tree—fully branched, with many leaves. By contrast, the lungs of a premature baby look like a young tree or sapling, with only a few branches and leaves.

"Just as a sparsely branched tree cannot function as well as a fully developed one, a premature baby's lungs have a harder time carrying out their functions of breathing and bringing oxygen to all the body's organs because they are underdeveloped. They also cannot fight off an infection such as respiratory syncytial virus (RSV) as well as the lungs of a full-term baby.”

-- Alan Cohen, MD, FAAP, FCCP
Pediatric Pulmonologist
Senior Director, Medical Affairs, MedImmune, Inc.

© 2005 MedImmune, Inc.

If Lungs Were Trees – Description of Infant Lung Development
Click here to download (PDF)