The pathway of oxygen in the breathing system can be described as follows:
- Oxygen enters the body through the nose or mouth during inhalation. The air is filtered, warmed, and humidified as it passes through the nasal cavity or oral cavity
- The air then travels down the pharynx (throat) and passes through the larynx (voice box)
- From the larynx, oxygen moves into the trachea (windpipe), which divides into the right and left primary bronchi, each leading to a lung
- Inside the lungs, the bronchi branch into smaller tubes called bronchioles, which continue to branch and become progressively smaller
- The bronchioles end in clusters of tiny air sacs called alveoli. These alveoli are the site of gas exchange and are surrounded by a dense network of capillaries (tiny blood vessels)
- Oxygen diffuses across the thin walls of the alveoli into the blood in the capillaries. This process is called diffusion and occurs because the alveolar and capillary walls are only one cell thick
- Oxygen binds to hemoglobin molecules in red blood cells and is transported via the bloodstream to the heart, which pumps oxygen-rich blood to tissues throughout the body
- In the body’s tissues, oxygen is released from red blood cells and diffuses into cells where it is used for cellular respiration to produce energy
- Carbon dioxide, a waste product of cellular respiration, diffuses from the cells into the blood and is carried back to the lungs to be exhaled
In summary, oxygen travels from the nose or mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli → diffuses into blood → transported to body tissues → used by cells for energy production
