Normal Lung

Each lung weighs about one pound. The lungs are composed of the conducting airways--the trachea and branching bronchi--and the alveoli where gas exchange occurs. Oxygen is taken into the blood stream, and carbon dioxide is transferred to the alveoli and exhaled. The alveolar gas exchange area is about the size of a tennis court, and destruction of alveoli will interfere with gas exchange.

Click here to view a diagram of the respiratory system. In the blue menu bar at the top, click Your Lungs and then Human Respiratory System to see the diagram. To get a definition of a label, click on it. To return to the diagram, click the "back" button in the menu bar. Remember to click the same "back" button to return to this page.

Normal Lung Removed from the Body

Side View

This lung has been inflated with air and dried. It retains the shape it had in the body. The lung is covered with a thin, smooth membrane called the pleura. Normally, the pleura is uniformly pale, but in most individuals, some black pigment from dust in the environment gets deposited in the pleura and appears as black spots, as seen here.

The lung is divided into lobes, two on the left and three on the right. This is a left lung with a diagonal fissure between the upper and lower lobes. The horizontal fissure in this case is a minor abnormality. The anterior part of the lung is to the left.

Section of Normal Lung

A slice of the dried lung shows the conducting airways (bronchi) cut in cross section or longitudinally. The rest is alveolar tissue and blood vessels. The blood vessels are not very apparent here because the blood has been drained from them.

Detail of a Slice of Lung

A closer view shows the small air spaces (alveoli) where gas exchange occurs. If you look carefully, you can see faint lines dividing the alveoli into lobules (arrows). The lobule has small airways (bronchioles) and branches of the pulmonary artery at the center and a pulmonary vein in the line at the edge.


Credit: Glantz S. Tobacco Biology and Politics, 2nd ed. HEALTH EDCO, WRS Group. Waco, TX 1999. <>

Note that components of the inhaled smoke cross into the blood stream in the lungs, travel to the heart, and then go to the brain, as well as other organs.