Ultrastructural studies of developing pulmonary alveolar septal elastin.

Eighteen fetal lambs have been studied at six different gestational ages ranging from 90 days to term. At 90 days gestation, only the microfibrillar component of elastin is present in pulmonary alveolar septal elastic fibers. The amorphous component appears at 110 days and gradually increases in amount, relative to microfibrils. At term (150 days), the composition of the pulmonary alveolar septal elastin resembles that of the adult ewe.