The respiratory system consists of an upper and lower respiratory tract. The upper respiratory tract includes the nasal cavity, pharynx and larynx and works to warm, moisten, and filter air before it reaches the lungs. The lower respiratory tract contains the trachea, bronchi and lungs and is responsible for gas exchange, supplying oxygen to the bloodstream and removing carbon dioxide. Diseases that can affect the upper respiratory tract include rhinitis, sinusitis, and pharyngitis.