The substance that moves from the bloodstream to the air via the lungs is carbon dioxide (CO₂).

Quick Scoop

Inside the lungs, tiny air sacs called alveoli sit right next to very small blood vessels (capillaries). Here, two key things happen at the same time:

  • Oxygen moves from the air into the blood , and
  • Carbon dioxide moves from the blood into the air so you can exhale it.

So, when the question is specifically “what moves from the bloodstream to the air via the lungs?”, the answer is carbon dioxide, a waste gas produced by your body’s cells.

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