The lung is often compared to a sponge that's filled with tiny bubbles or holes. The bubbles, surrounded by blood vessels, give the lungs a large surface to exchange oxygen and carbon dioxide. The airways and air sacs present in the anatomy of the lung are normally elastic, meaning they try to spring back to their original shape after being stretched or filled with air. In chronic obstructive pulmonary disease, much of the elastic quality is gone, and the airways collapse, obstructing airflow out of the lungs.
The lungs provide a very large surface area (the size of a football field) for the exchange of oxygen and carbon dioxide between the body and the environment.
A slice of normal lung looks like a pink sponge filled with tiny bubbles or holes. Around each bubble is a fine network of tiny blood vessels. These bubbles, surrounded by blood vessels, give the lungs a large surface to exchange oxygen (into the blood where it is carried throughout the body) and carbon dioxide (out of the blood). This process is called gas exchange. Healthy lungs do this very well.
You breathe in air through your nose and mouth. The air travels down through your windpipe (trachea) and then through large and small tubes in your lungs called bronchial (BRON-kee-ul) tubes. The larger ones are bronchi (BRONK-eye), and the smaller tubes are bronchioles (BRON-kee-oles). Sometimes the word "airways" is used to refer to the various tubes or passages that air must travel through from the nose and mouth into the lungs. The airways in your lungs look something like an inverted tree with many branches.
At the ends of the small bronchial tubes, there are groups of tiny air sacs called alveoli (al-VEE-uhl-EYE). The air sacs have very thin walls, and small blood vessels called capillaries run in the walls. Oxygen passes from the air sacs into the blood in these small blood vessels. At the same time, carbon dioxide passes from the blood into the air sacs. Carbon dioxide, a normal byproduct of the body's metabolism, must be removed.