The act of breathing out is known as

• A. Expiration
• B. Inspiration
• C. Inhalation
• D. Ventilation

Answer: (A)

Breathing out is the expiration phase of respiration. Expiration is the process by which air leaves the lungs; during quiet breathing it is usually passive, as the diaphragm and intercostal muscles relax, causing the chest cavity to shrink and air to be pushed out by increased intrathoracic pressure. The opposite phase, inspiration (inhalation), is air moving into the lungs when the diaphragm contracts and the chest expands. Ventilation refers to the overall movement of air into and out of the lungs, not to the act of exhaling alone. In situations of forced breathing, expiration can be active with abdominal muscles aiding the push. So the act of breathing out is expiration.