The respiratory system is composed of two main parts, the extrapulmonary airways and the lungs, and its main function is to carry out gas exchange between the body and the external environment. 1. Composition: The respiratory system is composed of two major parts: the extrapulmonary airways and the lungs. The extrapulmonary airways include the nose, pharynx, larynx, trachea and main bronchial tubes. The lungs are composed of all levels of bronchial tubes within the lungs as well as the alveoli. Generally, the nose, pharynx and larynx are called the upper respiratory tract, and the gas passages below the trachea (including all levels of bronchial tubes in the lungs) are called the lower respiratory tract. 2. Function: The function of the respiratory system is to carry out gas exchange, that is, inhalation of oxygen and exhalation of carbon dioxide. The body uses the inhaled oxygen to produce the energy needed for the body’s metabolism, and the carbon dioxide produced is discharged by the respiratory system. In addition, the pharynx is a common passage for food and gas, the nose has the function of smell, and the larynx has the function of pronunciation. It is recommended that patients with respiratory diseases should consult a doctor for a clear diagnosis and treatment under the doctor’s guidance.