The total area of adult alveoli is about 60-100m2, which is equivalent to the size of 25 ping-pong tables. The total alveolar area is composed of the area of 300-400 million alveoli, each alveolar size and shape varies, the average diameter is only 0.2mm, if each alveoli of the normal human lung is opened, the total area is many times the area of the human body surface. The alveoli are the functional unit of the lungs, and the oxygen inhaled by the body will be diffused to the blood through the respiratory membrane between the alveoli and capillaries, which has a high permeability due to the large area of the respiratory membrane, about 70m2, and an average thickness of less than 1μm, making the gas exchange very rapid. If part of the lung tissue is damaged or removed due to disease factors, the gas exchange function at the damaged site can be affected, but the healthy lung tissue compensates for the expansion and replaces the lung function of the defective alveolar tissue. If only one lobe or part of a lung segment is damaged, the rest of the lung tissue can compensate for the expansion, and with diet modification and proper exercise to help recovery, this injury has little effect on lung function. If two or even more lobes are damaged, the total alveolar area can be reduced by 1/2-1/3, and the remaining lung tissue can hardly compensate for the function of the defective lung tissue, and symptoms such as difficulty in breathing and cyanosis of the lips may occur. Patients with lung diseases should perform appropriate exercises, even for those who are bedridden for a long time, to enable the alveolar tissue in low hanging areas to open up through turning and patting the back, which not only helps to eliminate secretions and relieve local infections, but also helps to increase the alveolar area and improve lung function. Usually, we should try to reduce smoking and the impact of physical and chemical factors on lung tissue, so that lung tissue and alveolar elasticity can continue to stabilize at a relatively normal level, which helps maintain lung function.