What process occurs when lungs expel air?

The expulsion of air from the lungs is primarily known as passive expiration when it occurs as part of the normal respiratory cycle during rest. This process relies on the elastic recoil of the lungs and thoracic cavity without the active contraction of respiratory muscles. When the diaphragm and intercostal muscles relax after inhalation, the lungs naturally deflate due to their elastic nature, causing air to be pushed out of the lungs.

This process is efficient and requires little energy, making it the body's default mechanism for exhalation during normal breathing. In contrast, active expiration involves the use of additional muscles, like the abdominal muscles, to forcefully expel air, often seen during vigorous activities or exercises where a more substantial expulsion of air is required.

Inhalation refers to the process of taking air into the lungs, while forced inhalation is an intense version that requires muscular effort, which is unrelated to the expulsion of air. Thus, recognizing these distinctions highlights why the process of expelling air during regular breathing is categorized as passive expiration.