Exchange of Gases during Respiration: The Decrease in Oxygen Concentration in Expired Air Explained

What is the percentage of oxygen in expired air?


The percentage of oxygen in expired air is lower than that in inspired air due to the exchange of gases that occurs during respiration. The percentage of oxygen in expired air ranges between 15-18%, which is lower than the approximately 21% in inspired air. The reason for this decrease is that during respiration, the oxygen in inspired air diffuses from the lungs’ alveoli into the bloodstream, while carbon dioxide diffuses from the bloodstream into the lungs’ alveoli for expiration. As a result, the concentration of oxygen in expired air decreases, while the concentration of carbon dioxide increases. The exact percentage of oxygen in expired air may vary depending on several factors, including respiration rate, respiratory volume, and metabolic rate.

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