1. Inhalation: We breathe in air through our nose or mouth. This air is a mixture of gases, primarily nitrogen (about 78%) and oxygen (about 21%).
2. Passage through the respiratory system: The inhaled air travels down the trachea (windpipe), then through the bronchi, and finally into the tiny air sacs in the lungs called alveoli.
3. Gas exchange in the alveoli: The alveoli are surrounded by tiny blood vessels called capillaries. The thin walls of the alveoli and capillaries allow for the exchange of gases. Oxygen from the inhaled air diffuses across the walls of the alveoli and into the capillaries, where it binds to red blood cells. At the same time, carbon dioxide (CO2) produced by the body's cells diffuses from the capillaries into the alveoli to be exhaled.
4. Transportation by the circulatory system: The red blood cells carrying oxygen travel throughout the body via the bloodstream. The circulatory system delivers oxygen to all the tissues and organs that need it.
5. Cellular respiration: Oxygen is used in the cells to break down glucose (sugar) and produce energy in a process called cellular respiration. This process releases carbon dioxide as a waste product.
In summary:
* Inhale air containing oxygen.
* Oxygen diffuses from the alveoli into the blood.
* Red blood cells carry oxygen throughout the body.
* Cells use oxygen for energy production.
* Carbon dioxide is released as a waste product and is exhaled.
