What physiological adjustment helps expel air from the lungs?

• A. Contraction of the diaphragm
• B. Relaxation of the diaphragm
• C. Expansion of the intercostal muscles
• D. Increase in tidal volume

Answer: (B)

The physiological adjustment that helps expel air from the lungs is the relaxation of the diaphragm. During normal breathing, inspiration occurs when the diaphragm contracts and moves downward, creating a negative pressure that draws air into the lungs. When it comes time to exhale, the diaphragm relaxes and moves back up into its resting position. This relaxation decreases the volume of the thoracic cavity, increasing the pressure inside the lungs relative to the outside atmosphere, which effectively forces air out of the lungs.

This process is part of normal tidal breathing, where both the contraction and relaxation of the diaphragm play distinct roles in the breathing cycle. The other options, such as contraction of the diaphragm and expansion of the intercostal muscles, are primarily involved in the process of inhalation rather than exhalation. An increase in tidal volume refers to the amount of air breathed in or out during normal breathing and does not directly correspond to the mechanisms of air expulsion from the lungs.