1.2.6 –1.2.10 The respiratory system GapFill

The composition of oxygen in inspired air is ~  16212712%, with nitrogen making up the bulk at ~78% and a combination of other gases at <1% (including  carbon monoxidecarbon dioxidehydrogenmethane at ~0.4%). The composition of expired air is ~  190.02166% oxygen and   210.78164% carbon dioxide, with the rest being made up of ~78% nitrogen, which is unchanged as it is inert in the human body. The change in values of oxygen and carbon dioxide is as a result of gaseous exchange, whereby oxygen is used by tissues, e.g. skeletal muscle for  aerobicgaseousanaerobicshort-term respiration, while carbon dioxide is produced as a by-product that needs removing.

During exercise, the composition of inspired and expired air remains relatively stable, although the volume of each vastly increases. This change, among others, is expressed below.

•  Tidal volumeExpiratory reserve volumeBreathing rateInspiratory reserve volume – the number of breaths taken per minute is typically increased from 12 breaths per minute to up to 40–60 breaths per minute.
•  Tidal volumeExpiratory reserve volumeBreathing rateInspiratory reserve volume – the volume of air expired per breath also increases from a typical resting value of 0.5 mL to up to 4,500 mL during high-intensity exercise.
• Minute ventilation – the volume of air inspired or exhaled per minute also increases as a result of increases to the above two values.
•  Vital capacityBreathing rateTidal volumeInspiratory reserve volume – the maximum volume of air that can be expired from the lungs after maximal inhalation remains unchanged.