Why does the air pressure in the lungs decrease and be lower than atmospheric pressure when inhaling, and increase and be higher than atmospheric pressure when exhaling? (adopted by the person who ans

Why does the air pressure in the lungs decrease and be lower than atmospheric pressure when inhaling, and increase and be higher than atmospheric pressure when exhaling? (adopted by the person who answers best) The exchange of gas between the lungs and the outside world is realized through respiratory movement. When inhaling, the contraction of respiratory muscles makes the vital capacity increase with the expansion of the lungs, making the air pressure in the lungs lower than the external atmospheric pressure, and the external air enters the lungs. When exhaling, the air pressure in the lung is higher than the outside atmospheric pressure, and the air in the lung is discharged. When inhalation has just stopped and exhalation has not started, there is no pressure difference between the lungs and the outside world, that is, the air pressure in the lungs is equal to atmospheric pressure. When the inhalation is just stopped, the gas in the lungs has been exchanged with the blood, so the oxygen content in the lungs is lower than that in the air. At the same time, it is impossible to completely expel the gas in the lungs every time you exhale, so the oxygen content in the lungs is lower than that in the air.