Expiração

Expiração refers to the process of releasing air from the lungs. It is the second phase of the respiratory cycle, following inspiration (inhalation). During expiration, the diaphragm relaxes and moves upward, while the intercostal muscles also relax, causing the rib cage to move downward and inward. This decrease in the volume of the thoracic cavity leads to an increase in intra-alveolar pressure, forcing air out of the lungs.

Normal, resting expiration is a passive process. However, forced expiration, such as during coughing or heavy exertion, involves the active contraction of abdominal and internal intercostal muscles. These muscles further reduce the volume of the thoracic cavity, increasing the pressure gradient and expelling air more forcefully. The rate and depth of expiration can be voluntarily controlled to some extent.

The primary function of expiration is to remove carbon dioxide, a waste product of metabolism, from the body. This gas exchange occurs in the alveoli of the lungs, where carbon dioxide diffuses from the blood into the air sacs to be expelled. The composition of exhaled air is significantly different from inhaled air, containing a higher concentration of carbon dioxide and water vapor, and a lower concentration of oxygen. Expiration also plays a role in vocalization, as the controlled release of air through the vocal cords allows for the production of sound.