Across Down 1. important respiratory muscle 2. delicate air sacs 4. shoehorn-shaped 3. covers the outer surfaces of the lungs ( 2 word 6. entryway of the nose guarded by hairs that 5. windpipe screen out large particles 7. separates the oral and nasal cavities (2 words 9. a chronic, progressive condition characterized 8. also known as dust cells by shortness of breath and an inability to tolerate 10. essential respiration organ physical exertion 11. respiratory center causes strong, sustained 12. common passageway of nose, mouth, and inspiratory movements throat 13. vocal cords that play no part in sound production 14. contains C -shaped tracheal cartilages that stiffen the tracheal walls and protect the airway 15. oily secretion that keeps the alveoli from collapsing .