Why does air enter the lungs during inhalation?

May 13, 2025 Source: Cainiu Health

Dr. Ren Yi

Introduction

Air enters the lungs during inhalation, primarily as a result of the coordinated action of respiratory muscle contractions, changes in thoracic cavity volume, decreased air pressure within the lungs, unobstructed airways, and alveolar expansion. It is important to pay attention to respiratory health in daily life and maintain good lifestyle habits, such as quitting smoking, avoiding air pollution, and engaging in regular exercise, in order to protect lung function.

Under normal circumstances, the process of air entering the lungs during inhalation mainly results from the combined effects of respiratory muscle contraction, changes in thoracic cavity volume, decreased intrapulmonary pressure, unobstructed airways, and alveolar expansion. A detailed analysis is as follows:

1. Respiratory Muscle Contraction: During inhalation, the contraction of respiratory muscles such as the intercostal muscles and the diaphragm causes the ribs to move upward and outward, while the top of the diaphragm descends. This increases the volume of the thoracic cavity. This action serves as the foundation of the inhalation process and provides the power for air to enter the lungs.

2. Changes in Thoracic Cavity Volume: As the respiratory muscles contract, the thoracic cavity expands, leading to a relative decrease in pressure within the lungs. Since atmospheric pressure remains constant and stable, the reduced pressure inside the lungs allows outside air to naturally flow into the lungs along the pressure gradient.

3. Decreased Intrapulmonary Pressure: As the thoracic cavity enlarges, the lungs expand accordingly, causing the air within them to become diluted and intrapulmonary pressure to drop. This pressure difference is the direct cause of air entering the lungs.

4. Unobstructed Airways: For air to reach the lungs, it must pass through the nasal cavity, pharynx, larynx, trachea, and bronchi. These airway passages must remain open and free from obstruction or narrowing to allow air to flow smoothly into the lungs.

5. Alveolar Expansion: As inhalation proceeds, the alveoli gradually expand, providing additional space for air storage. The extensive network of capillaries surrounding the alveoli also provides a large surface area for gas exchange between oxygen and carbon dioxide.

In daily life, it is important to maintain respiratory health by adopting healthy lifestyle habits such as quitting smoking, avoiding air pollution, and engaging in regular physical exercise to protect pulmonary function.

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