How many and what stages does the process of respiration consist of?

Distinguish: a) external respiration – processes occurring in the respiratory organs, due to which oxygen from the external environment enters the blood, and carbon dioxide – into the external environment; b) transport of gas by blood – saturation of organs with oxygen and release of carbon dioxide; c) tissue or intracellular respiration – the oxidation of organic compounds in the cells of the body, accompanied by the consumption of oxygen, the formation of carbon dioxide and the release of energy, which is used for vital processes.