You are viewing an organ of the respiratory system and note the following tissues: folded mucosal layer containing simple cuboidal epithelium and smooth muscle. Identify the organ.

A) Respiratory bronchiole
B) Terminal bronchiole
C) Alveolar duct
D) Alveolus

Respiratory Bronchiole

The smallest air passages in the lungs where gas exchange occurs, connecting the terminal bronchioles to alveolar sacs.

Terminal Bronchiole

The terminal bronchiole is the smallest airway in the respiratory tract that conducts air and does not engage in gas exchange.

Alveolar Duct

Tiny ducts in the lungs that connect the respiratory bronchioles and alveolar sacs, a key part in the pathway of air to the alveoli.