Video narration
How does one breath reach every cell in your body? Think of a balloon: pressure changes move air. But lungs are not simple bags. Air enters through nose or mouth, travels down the trachea, and splits through branching airways deep into your chest. Here's the crucial turn: the lungs do not pull air in themselves. The diaphragm, muscle beneath them, contracts and moves downward. Chest volume increases, pressure falls, and air flows in. When it relaxes, pressure rises and air flows out. At the ends of those branches are alveoli-tiny air sacs wrapped in blood vessels. There, oxygen crosses into the blood, while carbon dioxide crosses out to be breathed away. The heart and blood carry that oxygen onward. So the lungs do more than hold air: they move it to the exchange surface that loads your blood. That is how one breath reaches every cell.