By taking in oxygen from the air and expelling carbon dioxide, the lungs play a crucial role in maintaining life. The oxygen gathered by the lungs enters the blood as it circulates and is distributed to cells throughout the body. Of all the body's organs, the lungs, which are not yet fully mature at birth, account for the greatest number of health problems in infants and young children, including viral and bacterial infections, asthma, and obstruction from swallowing or inhaling foreign objects and substances.
During the prenatal stage, the lungs are among the last organs to finish developing. The surfactant coating that keeps them from sticking together isn't formed until the last month or two of gestation. The air sacs (alveoli) at the ends of the bronchial tubes are formed last and continue developing for some time after birth: the lungs of infants have only one-tenth as many air sacs as those of adults. The unborn baby, who is suspended in fluid, does not need lungs yet because the placenta exchanges oxygen and carbon dioxide, performing the task the lungs will later assume. The lungs themselves are also filled with fluid, most of which is expelled during the birth process. After birth, the chest expands and takes in air for the first time as the infant takes her first breath. After the first few breaths, the lungs should be fully expanded, and the air sacs fully inflated within an hour. Deep breathing begins about 30 seconds after birth, and respiration should total 30 to 60 breaths per minute by the time the infant is 90 minutes old. The lungs are pale pink at birth, eventually becoming darker as a result of inhaling dust and other particles.