Alveolar Respiration

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As air is inhaled, it travels through the bronchi and bronchioles and reaches the alveoli—tiny air sacs surrounded by capillaries (Figure 1). This is where gas exchange takes place. Oxygen moves from the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli to be exhaled. This exchange happens by diffusion: Gases move from areas of high concentration to low concentration. Because both alveolar and capillary walls are just one cell thick, diffusion occurs rapidly and efficiently. This alveolar respiration facilitates cellular respiration.

Figure 1. Human Respiratory System

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As air is inhaled, it travels through the bronchi and bronchioles and reaches the alveoli—tiny air sacs surrounded by capillaries. This is where gas exchange takes place. Oxygen moves from the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli to be exhaled. This exchange happens by diffusion: Gases move from areas of high concentration to low concentration. Because both alveolar and capillary walls are just one cell thick, diffusion occurs rapidly and efficiently. This alveolar respiration facilitates cellular respiration, which we’ll look at next.

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