The exchange of carbon dioxide and oxygen between lung tissue and the bloodstream occurs in the

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The bronchioles end in microscopic ducts capped by air sacs, called alveoli. Each thin-walled alveolus is in contact with a blood capillary. This contact between the two structures allows the exchange of gases. It is at this point that oxygen (O₂) from the expired air moves across the one-cell membrane into the blood cells. Carbon dioxide (CO₂) moves in the other direction, from the blood into the air to be expired.

The Exchange of Carbon Dioxide and Oxygen Between Lung Tissue