Y alveoli

Alveoli are the site of gas exchange

The surface area available for gas exchange is increased by the lung alveoli. Alveoli are the terminal air spaces of the respiratory system and are the actual sites of gas exchange between the air and the blood. Each alveolus is surrounded by a network of capillaries that brings blood into close proximity to inhaled air inside the alveolus. About 150 to 250 million alveoli are found in each adult lung; their combined internal surface area is approximately 75 m2, roughly the size of a tennis court. Each alveolus is a thin-walled polyhedral chamber approximately 0.2 mm in diameter that is confluent with an alveolar sac (Fig. 18.14).

• Alveolar ducts are elongate airways that have almost no walls, only alveoli, as their peripheral boundary. Rings v , H* M

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