Lung This is a high magnification SEM of a tiny portion of a rabbit lung. Mammals, birds and reptiles have lungs, as do most amphibians and a few kinds of fish. In the chest the trachea divides into two branches, the bronchial tubes, that go to the lungs. The bronchial tubes eventually narrow down to bronchioles, about 1 mm or less in diameter. This is where the gas exchange takes place.
Blood comes in via arteries, and empties into veins which take it back to the heart.
Oxygen from the alveoli diffuses across the alveoli cells into the blood, where it is taken to the heart. At the same time, poisonous carbon dioxide which is a byproduct of animal metabolism, moves out of the blood and into the lungs, where it can be exhaled. There are a lot of diseases of the lung, the worst of which are caused by smoking tobacco. This rabbit's lung was very healthy and pink. This material may not be reproduced in any form without express written permission.