How does the pressure in the lungs and the pressure outside the lungs change when inhaling and exhaling?

When exhaling, gas can enter and leave the lungs, depending on the difference between the pressure in the lungs and the atmospheric pressure. When exhaling, the lungs contract, the air pressure in the lungs is higher than the external atmospheric pressure, and the gas is discharged from the lungs and discharged through the nostrils to complete exhalation.

When people inhale, the chest width expands autonomously, the chest volume becomes larger, and the air pressure in the chest is less than the external atmospheric pressure. Due to atmospheric pressure, air enters the lungs to complete inhalation.

Extended data

The whole breathing process is divided into three links: external breathing, gas transmission and internal breathing.

External respiration includes the ventilation activities of respiratory organs (taking mammals as an example, that is, the gas exchange process between alveoli and the external environment) and respiratory organs (taking mammals as an example, that is, the gas exchange between alveoli and alveolar capillary blood).

Gas transport is a process of transporting oxygen from respiratory organs to tissues and carbon dioxide from tissues to respiratory organs through circulating blood.

Internal respiration is the process of gas exchange between blood, tissues and cells in tissue capillaries, also known as tissue ventilation.

The direct motive force of lung ventilation is the pressure difference between lung pressure and atmospheric pressure, and the original motive force of lung ventilation is the rhythmic breathing movement caused by the contraction and expansion of respiratory muscles. Breathing in quietly is active, and exhaling is passive.

When breathing hard, both inhalation and exhalation are active. The inspiratory muscles are mainly diaphragm and extracostal muscles, and the expiratory muscles are mainly intercostal muscles.

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