Differences in Inspired & Expired Air
- Air that is breathed in and air that is breathed out has different amounts of gases in it due to exchanges that take place in the alveoli
- Atmospheric air contains around 20 – 21% oxygen, of which we only absorb around 4 – 5%, expired air contains around 16% oxygen
- Normal carbon dioxide content of air is around 0.04% and, as carbon dioxide diffuses into the alveoli from the blood, we expire air containing around 4% carbon dioxide
- The air we breathe out contains more water vapour (around 1%) than when we breathe it in which is variable
- The temperature of exhaled air is higher than inhaled air due to heat energy released from respiration
Composition of Air Table
Exam Tip
For those of you studying the extended syllabus you can read the explanation as to why inspired and expired differ here.