What is the oxygen pathway when we breathe in?

When we breathe in, oxygen enters through the nose or mouth and travels down the windpipe (trachea) into the lungs. In the lungs, oxygen is absorbed by tiny air sacs called alveoli and then enters the bloodstream through tiny blood vessels called capillaries. The oxygen-rich blood is pumped from the lungs to the rest of the body by the heart, where it is used for energy production in cells through a process called cellular respiration.