Conducting Zone pyright e The McGraw-Hill Companies, Inc. Permission required for reproduction or display all the structures air passes through before Larynx Thyroid cartilage reaching the Cricoid respiratory zone cartilage Cartilage holds tube system open and smooth muscle Trachea controls tube Carina diameter Left primary · Warms and Right primary Bronchus nchius humidifies inspired air Filters and cleans9 Conducting Zone • All the structures air passes through before reaching the respiratory zone. • Cartilage holds tube system open and smooth muscle controls tube diameter • Warms and humidifies inspired air. • Filters and cleans: Insert fig. 16.5