Lung capacity has evolved to support the animal's activities. During inhalation, the lungs expand with air and oxygen diffuses across the lung's surface, entering the bloodstream. During exhalation, the lungs expel air and lung volume decreases.

What happens to the volume of the lungs during exhalation?

When the lungs exhale, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out.

Does lung volume increase or decrease during expiration?

In contrast, expiration is a passive process. As the diaphragm and intercostal muscles relax, the lungs and thoracic tissues recoil, and the volume of the lungs decreases.