CORE TOPIC:

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Diagram of respiratory bronchioles

(1) Respiratory (terminal) bronchioles
Larger diameter bronchioles are lined by a ciliated, cuboidal epithelium without goblet cells which eventually decreases in height and complexity to become first cuboidal and finally the simple squamous epithelial lining of the alveolar ducts

(2) Alveolar ducts
Between 2 and 10 alveolar ducts open laterally from the respiratory bronchioles

(3) Alveoli
These are the final branches of the respiratory system. They are thin walled air sacs lined by an extremely attenuated epithelium across which diffusion occurs.

The walls of the bronchioles and alveolar ducts are composed of;