Inadequate production of which substance in premature newborns' lungs can lead to respiratory distress syndrome?

1. During weeks 21-30 of fetal development, the lungs begin producing a substance essential for proper expansion after birth. 2. This substance reduces surface tension within the lungs. 3. This substance is called surfactant. 4. Vernix caseosa is a skin coating and meconium is fetal stool, so neither affects lung surface tension. 5. Amniotic fluid is what fills the lungs before birth, but it is not the substance whose deficiency causes respiratory distress syndrome. 6. Because premature infants may not yet produce enough surfactant, they are at risk of respiratory distress syndrome and may need surfactant replacement therapy or CPAP. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 28 "Development and Inheritance", p.1340 §Other Organ Systems_