by Alicia M Prater PhD

Created on: February 23, 2009   Last Updated: April 16, 2010

The lungs are the largest organ of the respiratory system and located within the chest cavity. Lung diseases include more than just the well known lung cancer, but also alveolar disorders and obstructive disorders, such as COPD. First though, to understand the debilitating effects of lung disease, one must understand the structure and function of the lungs.

On a gross scale, the lungs are divided into lobes, three on the right side of the chest cavity and two on the left. The lack of a third lobe on the left side leaves room for the heart, which pumps blood directly to the lungs for oxygenation. The lungs receive air through the bronchi. The bronchial tree branches off the trachea, which is a fork off the pharynx, the cavity behind the mouth. The other fork off the pharynx is the esophagus, which carries food to the stomach. In the trachea is mucus that catches foreign particles and infectious agents before they can enter the lungs. Any irritation of this tube or alteration in the mucus secretion can lead to infection or obstruction in the airway, including aspiration of food from the esophagus. The trachea branches left and right into the lungs (left and right bronchus), which then branch further into increasingly smaller bronchioles that terminate in the alveoli.

In general, during inhalation, air enters the mouth or nose, passes through the pharynx, past the larynx (voicebox), through the trachea, and into the bronchial tree where it is disseminated to the lung tissue. Exhalation is the passive process of the pressure in the lungs readjusting to force out the air, which is less oxygenated than when it entered and containing carbon dioxide from the blood. The respiratory centers of the brain usually control this process involuntarily, and there is always some air reserve in the lungs to ensure efficient gas exchange, which is the basic function of the lungs. Lung diseases cause deviations in this process due to damage, infection, or genetic mutations.

The structure of the lung tissue accommodates the exchange of gases between the air breathed into the lungs from the external environment and the blood. This exchange occurs through the thin-walls of the lung tissue, the alveoli. The lung tissue is actually made of air sacs that expand when filled with air to increase the surface area across which gas can be exchanged. Among these air sacs are capillaries that carry blood close to the surface. Restricted expansion of the lung tissue, restricted blood flow to

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