How does gaseous exchange takes place in the body?

Respiration is the process of gaseous exchange by: External breathing, the oxygen is taken up by the capillaries of the lung alveoli

(air sacs) and expelled as carbon dioxide which is released from the blood. Internal, the stage of respiration in which oxygen is released to the tissues and carbon dioxide absorbed by the blood.

Visualise the lungs as upside down

trees

and the alveoli

as leaves.