Final answer:
Infant respiratory distress syndrome (IRDS) is characterized by a deficiency of the substance surfactant in the lungs, leading to difficulties in lung inflation and breathing for premature infants.
Step-by-step explanation:
The missing component in infant respiratory distress syndrome (IRDS) is surfactant. Surfactant is a critical substance that permits the lungs, especially the alveoli, to inflate properly.
In IRDS, a condition primarily seen in prematurely born infants, there is an insufficient production of pulmonary surfactant. This substance is vital as it reduces the surface tension within the alveoli, which are tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide occurs. Without adequate surfactant, the alveoli struggle to stay open, leading to difficulties in breathing and proper lung function.
Production of surfactant typically begins around 20 weeks of gestation, but it is not enough for lung inflation until later in the pregnancy. Thus, babies born before the adequate production of surfactant, especially around 26 weeks, often experience RDS because their lungs cannot inflate effectively, leading to low blood oxygen levels and other related health issues.