Inspired air (the air you inhale) and expired air (the air you exhale) differ in several key aspects, primarily in terms of their composition and the gases they contain.
1. Oxygen (O₂) Content
- Inspired Air: Contains a higher percentage of oxygen, around 21%.
- Expired Air: Has a lower percentage of oxygen because your body uses some of it during respiration. Typically, it contains about 16-17% oxygen.
2. Carbon Dioxide (CO₂) Content
- Inspired Air: Contains a very low amount of carbon dioxide, around 0.04%.
- Expired Air: Has a much higher concentration of carbon dioxide (about 4-5%) because it is a waste product produced by the body during metabolism and exhaled from the lungs.
3. Nitrogen (N₂) Content
- Inspired Air: Nitrogen makes up about 78% of the air you breathe in, and it remains largely unchanged during respiration.
- Expired Air: The nitrogen content remains relatively the same (around 78%) because it is not used by the body.
4. Water Vapor
- Inspired Air: Air you inhale may be dry depending on the environment but usually contains little to no water vapor when entering the lungs.
- Expired Air: Is typically saturated with water vapor due to the moisture added by the respiratory passages and the lungs.
5. Temperature
- Inspired Air: The air is generally cooler and must be warmed by the respiratory system to body temperature (about 37°C or 98.6°F) before entering the lungs.
- Expired Air: Is exhaled at body temperature because it has been warmed as it passed through the lungs.
6. Other Gases
- Inspired Air: It contains small amounts of other gases, such as argon and trace gases, in similar proportions to what is found in the atmosphere.
- Expired Air: These gases remain relatively unchanged but are present in smaller quantities compared to O₂ and CO₂.
Summary Table
| Component | Inspired Air | Expired Air |
|---|---|---|
| Oxygen (O₂) | ~21% | ~16-17% |
| Carbon Dioxide (CO₂) | ~0.04% | ~4-5% |
| Nitrogen (N₂) | ~78% | ~78% |
| Water Vapor | Low/None | High (saturated) |
| Temperature | Ambient | Body temperature (37°C) |
| Other Gases | Present in small amounts | Similar but in smaller quantities |
These differences reflect the process of gas exchange in the lungs, where oxygen is absorbed into the blood, and carbon dioxide is removed, along with the humidification of air in the respiratory system.