Question: what are the 4 main functions of the respiratory system?
Answer: The inhalation and exhalation of air or Breathing. ... 
Gas exchange between the lungs and the bloodstream (External Respiration). ... 
Gas exchange between the bloodstream and the body tissues (Internal Respiration). ... 
Vibration of the vocal cords in the larynx to produce Sound. ... 
The sense of Smell.