The process of inhalation and exhalation

The human body maintains life by continuously performing respiratory movements to facilitate gas exchange, thereby meeting the metabolic demands of the body. The processes of inhalation and exhalation are as follows:

① During inhalation, the diaphragm and intercostal muscles contract simultaneously, causing expansion of the thoracic cavity and descent of the diaphragmatic dome. This reduces the negative pressure within the thoracic cavity, allowing oxygen-rich air from the external environment to enter the alveoli via the airways. Oxygen then diffuses across the alveolar wall into the pulmonary capillaries.

② Capillaries transport carbon dioxide—produced as a metabolic byproduct—back into the alveoli.

③ During exhalation, the diaphragm and intercostal muscles relax, allowing the thoracic cavity to recoil elastically. This increases intrathoracic pressure, forcing carbon dioxide out of the body via the airways.