What does expiration refer to in the process of respiration?

Expiration refers specifically to the process of emptying air from the lungs. During this phase of respiration, the diaphragm and intercostal muscles relax, leading to an increase in pressure within the thoracic cavity, which pushes air out of the lungs. This process is essential for removing carbon dioxide from the body, as oxygen is taken in during the inhalation phase. Understanding expiration is crucial in the larger context of the respiratory cycle, which encompasses both inhalation and exhalation, where the body manages gas exchange and maintains homeostasis. The other options pertain to different aspects of the respiratory process, such as the intake of air (inhalation), gas exchange in the alveoli, and the uptake of oxygen by cells, but they do not describe the act of expiration itself.