Where blood is oxygenated?

Blood is oxygenated in the lungs. The lungs are a pair of organs located on either side of the heart. They are made up of millions of tiny air sacs called alveoli. The alveoli are lined with capillaries, which are tiny blood vessels. When you breathe in, oxygen from the air diffuses across the alveoli and into the capillaries. The oxygen-rich blood is then pumped by the heart to the rest of the body.