Because of the following

During inhalation, due to the contraction of respiratory muscles and the descent of the diaphragm, the chest cavity expands, the pleural cavity has negative pressure, the intrapulmonary pressure drops, and a pressure difference occurs between the intrapulmonary pressure and the atmospheric pressure. When the intrapulmonary pressure is lower than atmospheric pressure, air entering the lungs along the pressure difference is called inhalation. , so it is very smooth

The reason why gas can enter and leave the lungs during exhalation depends on the difference between the intrapulmonary pressure and the atmospheric pressure.

When the lungs shrink, the intrapulmonary pressure is higher than the atmospheric pressure, and the gas exits the lungs and is expelled through the nostrils, so it is reversed

Plagiarism from downstairs