Final answer:
Exhalation involves air flowing out of the lungs because the diaphragm relaxes, decreasing thoracic volume and increasing air pressure inside the lungs. It's a passive process due to lung elasticity but can be active with muscle involvement during controlled breathing. Alveoli in the lungs facilitate gas exchange and assist in passive exhalation.
Step-by-step explanation:
When you exhale, the diaphragm relaxes and moves upward, which diminishes the volume of the thoracic cavity and increases the air pressure inside your lungs. This difference in pressure between the inside of the lungs and the outside environment causes air to flow out of the lungs, much like air escaping from a balloon when its opening is released.
Exhaling is generally a passive process that relies on the elasticity of the lungs, but it can be an active process involving the internal intercostal and abdominal muscles during forced exhalation or activities that require controlled breathing such as swimming, yoga, or singing.
Our lungs host millions of small mucus-lined sacs called alveoli, where the exchange of oxygen and carbon dioxide takes place. These alveoli can contract due to surface tension, aiding in the expulsion of air during exhalation. For individuals using a positive pressure respirator or those who may have paralysis, the natural elasticity and surface tension in the alveoli allow air to be exhaled without muscle action.