There are five stages of the process of respiration:
pulmonary ventilation is the movement of air into and out of the lungs.
gas exchange is the exchange of oxygen and carbon dioxide between the respiratory units.
thransport of gases through the body of the blood.
gas exchange between the blood in the systemic capillaries and the tissue cells. ( internal respiration)
cellular respiration is the utilization of the oxygen and the product of carbon dioxide by the cells.