The respiratory system plays a vital role in maintaining metabolic balance during periods of work and exercise. The respiratory system includes the nose, mouth, pharynx, larynx, trachea, bronchial tree and lungs. The primary function of the respiratory system is to supply the blood with oxygen and remove carbon dioxide waste. Exercise increases the need for oxygen and results in a carbon dioxide build-up. The respiratory system also has many other functions in relation to the body’s metabolism. In the dog, two important functions of the respiratory system include thermoregulation and scent recognition. These functions play an important role in the performance of the athletic and working dog.