Exhalation

Exhalation

Diagram of the expiration process

Exhalation, also known as expiration, is the process of expelling air from the lungs through the airways to the external environment. It is a vital part of the respiratory cycle, which includes both inhalation and exhalation.

Physiology of Exhalation

Exhalation is primarily a passive process that occurs when the diaphragm and intercostal muscles relax. During inhalation, these muscles contract to expand the thoracic cavity, allowing air to flow into the lungs. When these muscles relax, the thoracic cavity decreases in volume, increasing the pressure inside the lungs relative to the outside atmosphere, causing air to flow out.

Muscles Involved

While exhalation is generally passive, certain conditions require active exhalation, which involves additional muscle groups:

• The internal intercostal muscles contract to pull the ribs downward and inward.
• The abdominal muscles contract to push the diaphragm upward.

These actions increase the pressure in the thoracic cavity, forcing air out more rapidly.

Control of Exhalation

The process of exhalation is controlled by the respiratory center in the medulla oblongata and the pons of the brainstem. These centers regulate the rhythm and depth of breathing by sending signals to the respiratory muscles.

Exhalation in Different Conditions

Exhalation can be affected by various physiological and pathological conditions:

• During exercise, the rate and depth of breathing increase, and active exhalation becomes more prominent.
• In conditions such as asthma or chronic obstructive pulmonary disease (COPD), exhalation can be impaired due to airway obstruction.

Related Pages

• Inhalation
• Respiratory system
• Lung
• Diaphragm (anatomy)