<span>The exchange happens between the blood through capillaries. Capillaries are the smallest sub unit of veins and arteries. When we breath in oxygen it goes through the lungs and transferred into the bronchi then into the bronchial tubes, then into the alveoli. Alveoli are small are sacs in the lungs the are microscopic and the exchange of gases then happens in the capillaries to oxygenate the blood.
