For speech, the vocal cords are drawn close together. In the alveoli, gases are dissolved in water, then transported across a single layer of cells between alveoli and capillaries. On breathing in, air is drawn down the trachea and into the bronchi. In each lung, the bronchi branch into bronchioles, which lead into the alveoli. Here, the carbon dioxide in blood brought from the heart in the pulmonary artery is exchanged for oxygen.
Oxygenated blood returns to the heart in the pulmonary vein.
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