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Lesson: Chapter 6 — Human body processes

Gas exchange in the alveoli 1 of 2

In the alveoli

Air from the nose passes down the trachea, bronchi and bronchioles and ends in the alveoli at the ends of the bronchioles, each wrapped in blood capillaries.

Figure to be added

Figure 6.10 — the air sacs of the lung: bronchioles ending in clusters of alveoli covered by a network of blood capillaries.

Oxygen

The concentration of O2 in the alveolar air is higher than in the blood of the capillaries, so O2 diffuses into the blood.

Carbon dioxide and water vapour

Their concentration in the blood is higher than in the alveolar air, so they diffuse into the alveoli and leave in the exhaled air.

Figure to be added

Figure 6.11 — inside an alveolus: oxygen diffusing into the red blood cells of the capillary and carbon dioxide and water vapour diffusing out.

The place where gases are exchanged between the outside and the blood is the respiratory surface. In humans it is the wall of the alveoli, and the gases cross it by diffusion.