"When children are born prematurely (before 36 weeks of gestation), their organs are not as prepared as those of full term children to handle functioning in the outside world. As a result, the most important bodily functions become circulation, breathing air effectively and efficiently, and carrying oxygen to the organs.
Premature birth interrupts the final stages of normal lung development. If lungs were to be represented as an upside-down tree, the lungs of a full-term baby would be fully branched with many leaves. The lungs of a premature baby would look like a simple tree or sapling and would be very rudimentary, with only a few branches and leaves. Since the body counts on those branches to breathe, a simple tree cannot function as well as a fully developed tree.
The illustration graphically shows how the lungs of a premature baby differ from a full-term infant and why a disease such as Respiratory Syncytial Virus (RSV) can be so serious. A premature baby’s lungs are underdeveloped and cannot fight an infection such as RSV as well as a full-term baby’s can.”
– Alan Cohen, MD, FAAP, FCCP