The main function of the respiratory system is gaseous exchange. This refers to the process of Oxygen and Carbon Dioxide moving between the lungs and blood. Diffusion occurs when molecules move from an area of high concentration (of that molecule) to an area of low concentration. This occurs during gaseous exchange as the blood in the capillaries surrounding the alveoli has a lower oxygen concentration of Oxygen than the air in the alveoli which has just been inhaled.

Both alveoli and capillaries have walls which are only one cell thick and allow gases to diffuse across them.

The same happens with Carbon Dioxide (CO2). The blood in the surrounding capillaries has a higher concentration of CO2 than the inspired air due to it being a waste product of energy production. Therefore CO2 diffuses the other way, from the capillaries, into the alveoli where it can then be exhaled.

To demonstrate the use of Oxygen and Carbon Dioxide in respiration you can look at the amounts of both gases which we inhale and then exhale. The air we breathe contains approximately 21% Oxygen and 0.04% Carbon Dioxide. When we exhale there is approximately 17% Oxygen and 3% Carbon Dioxide. This shows a decrease in Oxygen levels (as it is used in producing energy) and an increase in Carbon Dioxide due to it being a waste product of energy production.

Related Articles

Mechanics of Breathing

The action of breathing in and out is due to changes of pressure within the thorax, in comparison with the outside. This action is also known as external respiration. When we inhale the intercostal...

Respiratory Volumes

Respiratory volumes are the amount of air inhaled, exhaled and stored within the lungs at any given time. Tidal Volume:The amount of air which enters the lungs during normal inhalation at rest. The...

The Respiratory System

The function of the human respiratory system is to transport air into the lungs and to facilitate the diffusion of Oxygen into the blood stream. Its also receives waste Carbon Dioxide from the blood and...

What is VO2 Max?

VO2 max is the measure of the peak volume of Oxygen (VO2) you can consume and use in a minute and is a popular measure of an athletes aerobic fitness. It is measured in ml/kg/min. The per kilogram...