What are the tiniest tubes in lung called?

The tiniest tubes in the lungs are called bronchioles. They are the smallest branches of the bronchial tree, and they connect the larger bronchi to the alveoli, which are the tiny air sacs where gas exchange takes place. Bronchioles are lined with ciliated cells that help to move mucus and foreign particles out of the lungs, and they also contain smooth muscle cells that can constrict or relax to regulate airflow.