What are the primary functions of the respiratory system?

(1) Provide an extensive area for gas exchange between inhaled air and the circulation; (2) move air to and from the exchange surfaces of the lungs; (3) protect the respiratory surfaces from dehydration, temperature changes, and other environmental variations and defend the respiratory system and other tissues from invasion by pathogens; (4) produce sounds involved in speaking, singing, or nonverbal auditory communication; (5) direct incoming air to the olfactory epithelium in support of olfaction; (6) indirectly contribute to regulation of blood volume, blood pressure, and  pH.