are the small sacs that are the site of gas exchange in the lungs. In addition to being an airway, the is the location of the human vocal cords. Cilia in cells along the trachea and nasal passages secrete which traps dirt and particles from the air. Air is only approximately 21% oxygen. The majority of air is . The medulla oblongata controls the contraction and relaxation of the , causing the lungs to inflate and deflate during breathing. Explain the process of breathing. Begin with inhalation and describe the route that the air takes to the lungs, and what happens when the air reaches the lungs. Include in your description the terms: mouth, nose, pharynx, larynx, trachea, bronchi, lungs, alveoli, carbon dioxide, oxygen, and capillaries