Describe the differences in composition between inspired and expired air, limited to: oxygen, carbon dioxide and water vapour

The composition of inspired (inhaled) air and expired (exhaled) air differs significantly, particularly in terms of oxygen, carbon dioxide, and water vapor. Here’s a concise breakdown of these differences:

1. Oxygen (O₂)

• Inspired Air: Contains approximately 21% oxygen.
• Expired Air: Contains about 16% oxygen.
• Difference: The decrease in oxygen content in expired air is due to its absorption by the body during respiration for metabolic processes.

2. Carbon Dioxide (CO₂)

• Inspired Air: Contains about 0.04% carbon dioxide.
• Expired Air: Contains around 4% carbon dioxide.
• Difference: The increase in carbon dioxide in expired air results from its production as a waste product of cellular respiration, which then diffuses from the blood into the alveoli.

3. Water Vapor

• Inspired Air: Typically has a lower concentration of water vapor.
• Expired Air: Generally contains a higher concentration of water vapor.
• Difference: The increase in water vapor in expired air occurs because moisture evaporates from the moist surfaces of the respiratory tract and alveoli during exhalation, reflecting body temperature.