The functions of the respiratory system mainly include the following: First, the most important is the respiratory function, which can inhale oxygen and exhale carbon dioxide, and there is gas exchange within the alveoli and between the pulmonary capillaries, which can provide sufficient oxygen to the airways and tissues of the whole body to ensure normal metabolism. Second, also has a certain defense function, can breathe in the air in the respiratory tract through nasal heating and filtration, but also through the cilia movement of the trachea, contraction, coughing, sneezing and other forms of foreign bodies and abnormal secretions out of the body. Third, it can also help metabolism, also has a neuroendocrine function, if there is a lesion in the lungs will not only affect the breathing, but also affect the whole body causing systemic diseases.