What is exhalation?

Exhalation is indeed characterized as a passive process during which the intercostal muscles and diaphragm relax. When the diaphragm, which is a dome-shaped muscle at the base of the thoracic cavity, relaxes, it moves upwards, reducing the volume of the thoracic cavity. Similarly, the intercostal muscles, which are located between the ribs, also relax, allowing the rib cage to return to its resting position. This combination of relaxation leads to a decrease in lung volume, which causes air to flow out of the lungs.

During this process, exhalation does not require active muscular effort; rather, it occurs due to the elastic recoil of lung tissue and the thoracic cavity. This efficient mechanism allows for the expulsion of carbon dioxide-rich air from the lungs without the need for active contraction of muscles, which distinguishes it from inhalation, where muscles actively contract to draw air in. Understanding this passive nature is essential for grasping basic respiratory physiology.