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Structure and function of the
alveoli
At the end of each alveolar
duct there are a number of sac-like structures called alveoli,
it is within these structures that surfactant is produced.
The alveoli are grouped together like a lot of interlinked
caves, rather than existing as separate individual sacs.
Gas exchange of oxygen and
carbon dioxide takes place in the alveoli. Oxygen from the
inhaled air diffuses through the walls of the alveoli and
adjacent capillaries into the red blood cells. The oxygen
is then carried by the blood to the body tissues. Carbon dioxide
produced by the body’s metabolism returns to the lung
via the blood. It then diffuses across the capillary and alveolar
walls into the air to be removed from the body with expiration.
The alveoli have a structure specialised for efficient gaseous
exchange:
- Walls are extremely
thin.
- They have a large
surface area in relation to volume.
- They are fluid
lined enabling gases to dissolve.
- They are surrounded
by numerous capillaries.
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