How Do We Breathe?

In the human body there is a respiratory tract which is composed of the nose, pharynx, throat, windpipe and bronchus. When the nose inhales the air, it goes into the lung through the throat, windpipe and bronchus. In the lung there are a lot of pulmonary alveoli on which are a lot of blood capillaries. When the air goes into the pulmonary alveoli, part of the oxygen enter-s into the blood capillaries. Then the oxygen is taken to the other parts of the body by the blood, to meet the needs of the body. At the same time, the blood capillaries, the waste air back to the pulmonary alveoli, and it is then exhaled by the respiratory tract.