The lungs gets oxygen when we inhale. Deoxygenated blood goes to the alveoli to become oxygenated blood. That is, oxygen from the lungs will be transferred to the blood and the carbon dioxide in the blood will be transferred to the lungs to be exhaled. Oxygenated blood goes back to the heart to be pumped throughout the body. This becomes deoxygenated once the blood delivers the oxygen to the whole system.
It’s just a cycle, so this just repeats over and over.
