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The lungs are the largest organ of the respiratory system, making up the majority of the lower respiratory system, the portion of the system located within the chest cavity. To understand the debilitating effects of lung disease, one must first understand the structure and function of the lungs.

The function of the lungs is to exchange gases between the air breathed into and out of the lungs from the external environment and the blood. This occurs through the thin walled lung tissue, the alveoli. The lung tissue is actually made of air sacs that expand when filled with air to increase the surface area through which gas can be exchanged. Among these air sacs are capillaries that carry blood close to the surface for exchange. Restrictions in the expansion of the lung tissue, the blood flow to the alveolar sacs, or obstruction of air flow into the alveoli result in compromised gas exchange, and ultimately a lack of oxygen in the blood.

On a larger 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. The trachea branches left and right into the lungs (left and right bronchus). They 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 for blood oxygenation. Exhalation is the passive process of the pressure in the lungs readjusting to force out the carbon dioxide that was exchanged out of 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. Lung diseases are deviations in this process due to damage, infection, or genetic mutations.

Alveoli disorders

-Hyaline membrane disease, also known

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