Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, 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.
Blood with fresh oxygen is carried from your lungs to the left side of your heart, which pumps blood around your body through the arteries. Blood without oxygen returns through the veins, to the right side of your heart
