The main gases found in the blood are oxygen and carbon dioxide.
Oxygen enters the blood from the air in the alveoli of the lungs in exchange for carbon dioxide, where it binds with the haemoglobin in the red blood cells to form oxyhaemoglobin. This is carried to individual cells of the body where cellular respiration takes place.
Carbon dioxide is produced as a waste product of chemical reactions in the cells, and transported in the blood as a weak acid solution in the blood serum.
In arterial blood, oxygen has a 'partial pressure' of 75 to 100 mm of mercury, whilst carbon dioxide measures between 35 and 45 mm mercury. The amount by which these gases deviate from the norm is a good indicator of lung function and capability.
