The exchange of gases O2 and CO2 in a mammal takes place in
Alveoli
Alveoli are the tiny sac-like structures which provide the interphase for the exchange of O2 and CO2. The exchange takes place between the millions of alveoli in the lungs and the capillaries that envelop them. The inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.