What is common between alveoli of the lung parenchyma and soap bubbles is the low surface tension of its wall.

Surfactant is a lipoprotein produced by pneumocyte type II cell lining the alveoli that lowers the inner surface tesnion of alveoli in order to be able to be filled with air and to exhale leaving residual air with collapsing.

Premature babies might be born with Respiratory Distress Syndrome (RDS), that’s why pregnant women may take a corticosteroid dose injection to stimulate the production of surfactant if she is at risk of premature delivery.

Lung H&E x100