Which gas is primarily expelled from the lungs during exhalation?

During exhalation, the primary gas expelled from the lungs is carbon dioxide. This gas is a byproduct of the metabolic processes that occur in the body's cells. When cells consume oxygen for energy, they produce carbon dioxide as a waste product, which then enters the bloodstream. As blood flows through the lungs, carbon dioxide is exchanged for oxygen through the alveoli, tiny air sacs where gas exchange occurs.

When we exhale, the diaphragm and other respiratory muscles relax, forcing air, which is rich in carbon dioxide, out of the lungs. While some oxygen is also present in exhaled air, the focus is on the removal of carbon dioxide to maintain proper acid-base balance within the body. This process is critical in ensuring that the body can efficiently remove waste gases that can lead to respiratory distress if allowed to accumulate.

In contrast, while nitrogen and helium are present in the atmosphere and can be inhaled, they do not play a significant role during normal respiration, as they are not used by the body in the same way oxygen and carbon dioxide are.