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When you breathe, air flows in through your mouth and nose and down your airways. Inside your lungs, the airways end in clusters of air-filled sacs. These air sacs are surrounded by tiny blood vessels. Here, oxygen from your lungs passes into your bloodstream to get to tissues throughout your body. Carbon dioxide is breathed out. This video is by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health (NIH). Learn more: Follow us on Twitter: Like us on Facebook:
