Chemoreceptors are receptors which are able to detect the presence and amount of various chemical substances and send the information to the central nervous system.
They are mostly active in the nose and taste organs, where they receive and transfer chemical images from the outer world. However, there are also chemoreceptors which receive and transfer chemical information about the inner world, especially about the chemical qualities of blood. Most of these are situated in the brainstem and large arteries (aortic and carotid bodies) of the body. Here they monitor the level of hydrogen ions in the blood, which is altered by a range of chemical disturbances. For example they are stimulated when there are low levels of oxygen (arterial hypoxia), high levels of carbon dioxide (hypercapnea) and high acidity (acidemia) in our blood. Via the appropriate feedback cycles our breathing volume and heart rate are then increased to rebalance oxygen and carbon dioxide levels and restore the normal acidity (pH). See also baroreceptors.
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