Oxygen enters the blood in the lungs through the process of [[1]].

Oxygen enters the blood in the lungs through the process of diffusion. The oxygen-rich blood is then pumped to the rest of the body by the heart.

Oxygen diffuses from the alveoli, where it is inhaled, into the capillaries surrounding the alveoli. This occurs due to the concentration gradient of oxygen, with a higher concentration of oxygen in the alveoli compared to the capillaries. Oxygen then enters the red blood cells, where it is bound to hemoglobin and transported to the body's tissues.