How does oxygen from the air get into the blood and organs? Where exactly in the lungs does this happen? It happens in the alveoli☝🏻 The alveoli are the final part of the respiratory apparatus - they look like bubbles or sacs. Through the entire bronchial tree, air enters them. So, the little capillaries that permeate these alveoli are just the ones responsible for gas exchange. When you breathe in, the arterial blood "comes in" and enriches with oxygen, carrying it to the rest of the body. And when we exhale, the venous blood gives back the carbon dioxide "collected" in the body, getting rid of it.