The Lungs

The lungs are two spongy organs surrounded by a thin, moist membrane called the pleura. They are the largest organs in our body. Each lung is composed of smooth, shiny lobes; the right lung has three lobes and the left has two. Approximately 90% of the lung is filled with air and only 10% is solid tissue.

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When a person inhales, air travels through the following pathways into the lungs.

• Air is carried from the trachea (the windpipe) into the lung through flexible airways called bronchi.
• Like the branches of a tree, bronchi divide successively into over a million smaller airways called bronchioles.
• The bronchioles lead to grape-like clusters of microscopic sacs called alveoli.
• In each lung of an adult there are millions of these tiny alveoli, which are composed of a thin membrane through which oxygen and carbon dioxide pass to and from capillaries.
• During deep inhalation, the elastic alveoli unfold and unwind to allow this passage to occur.
• Capillaries, the smallest of our blood vessels, carry blood throughout the body.
• Red blood cells contain factors that fight pollutants; white blood cells are the critical infection fighters in our body.