We have a well developed respiratory system comprising two lungs and
associated air passages to perform this function.
The first step in respiration is breathing by which atmospheric air is taken in
(inspiration) and the alveolar air is released out (expiration). Exchange of O2 and
CO2 between deoxygenated blood and alveoli, transport of these gases throughout
the body by blood, exchange of O2 and CO2 between the oxygenated blood and
tissues and utilisation of O2 by the cells (cellular respiration) are the other steps