How does the oxygen from the air you breathe in reach the cells that need it? What body system is involved?

The oxygen from the air we breathe in reaches the cells that need it through the circulatory system. The process involves several steps:<br /><br />1. **Respiratory System**: When you inhale, oxygen-rich air enters your lungs. In the alveoli, tiny air sacs in the lungs, oxygen diffuses into the blood in the capillaries surrounding them.<br /><br />2. **Circulatory System**: Oxygen binds to hemoglobin molecules in red blood cells, forming oxyhemoglobin. The heart then pumps this oxygenated blood through the pulmonary veins to the left side of the heart, which subsequently pumps it through the systemic circulation to the rest of the body.<br /><br />3. **Transport**: Oxygen-rich blood travels through arteries and arterioles to capillaries in tissues and organs. At the capillary level, oxygen diffuses from the blood into the cells where it is needed for cellular respiration, a process that produces energy.<br /><br />4. **Cellular Respiration**: Inside the cells, oxygen is used to produce ATP (adenosine triphosphate), the primary energy carrier in cells. This process also produces carbon dioxide as a byproduct.<br /><br />5. **Return to the Lungs**: Deoxygenated blood, now carrying carbon dioxide, returns to the heart via the veins and is pumped to the lungs through the pulmonary arteries. In the lungs, carbon dioxide diffuses into the alveoli to be exhaled.<br /><br />In summary, the oxygen from the air we breathe is transported to the cells by the circulatory system, specifically through the blood, which carries oxygen to tissues and organs and returns carbon dioxide to the lungs for exhalation.