Alveolus

Eventually the bronchioles come to a small cavity, pit or hole with a sac.

The Alveolus (singular) is a tiny air sac within the lungs where the exchange of oxygen and carbon dioxide take place.

At the alveolus the blood passes close by to be oxygenated and carbon dioxide taken away

All violas (Alveolus) are in a large sack (sac), they had arrived for the chamber orchestra.

Note: alveolus is one; alveoli is more than one.

Eventually the bronchioles come to a dead end, like a set of interconnected caves. Each one is called an alveolus (plural: alveoli).

Annotated diagram of the structure of alveolus

Here you can see the alveoli at the end of the bronchioles.

Position of alveolus in the lungs

There are as many as 170,000 alveoli per cm³.

Magnification of an alveolus where CO2 passes into and oxygen passes out into the blood

The alveolus is a sac which allows gas exchange of oxygen and carbon dioxide by diffusion. The alveoli have thin walls to aid this diffusion.

Diagram showing the blood capillaries around an alveolus

A network of tiny blood vessels, called capillaries, covers the surface of the alveolus to facilitate oxygen and carbon dioxide exchange.

Diagram showing the network of blood vessels around an alveolus

This diagram shows how the blood vessels spread all around the alveoli. The blood in the capillaries is very close to the alveoli, enabling oxygen to diffuse from the inhaled air into the blood, while carbon dioxide diffuses out of the blood into the alveolus sac ready to be exhaled.

NOTE

Alveolus (the ‘us’ is singular)

The Alveoli (the ‘i’ is plural)