Exhalation begins when the inspiratory muscles, including the diaphragm, relax. As the diaphragm relaxes, it moves upward into the thoracic cavity, causing the volume of the thoracic cavity and lungs to decrease. This decrease in volume increases the pressure inside the lungs, forcing air out of the lungs and initiating exhalation.
Mechanism of Exhalation
- The diaphragm and external intercostal muscles relax.
- The thoracic cavity volume decreases as the diaphragm moves upward.
- The pressure inside the lungs rises above atmospheric pressure.
- Air flows out of the lungs due to the pressure gradient.
Additional Details
- Exhalation is generally a passive process during quiet breathing.
- Forced exhalation involves contraction of abdominal muscles and internal intercostals to push air out more forcefully.
Thus, exhalation begins when the inspiratory muscles, especially the diaphragm, relax, leading to the recoil of lungs and expulsion of air.
