The upper respiratory tract (nose, trachea, and bronchi) has pseudostratified columnar epithelium that protects the lungs. The epithelium’s goblet cells release mucus to catch particles and inhibit further passage.

The lungs include spongy tissues with capillaries and roughly 30 million small sacs called alveoli. The alveoli are lined with thin simple squamous epithelium that allows air entering the alveoli to exchange its gases with the blood passing through the capillaries.

Hyaline cartilage is found in the larynx, trachea, and bronchi. It provides stability and helps to prevent the trachea from collapsing and blocking off the airways