Pneumonia

In order to better understand pneumonia, it is important to understand the basic anatomic features of the respiratory system. The human respiratory system begins at the nose and mouth, where air is breathed in (inspired), and out (expired). The air tube extending from the nose is called the nasopharynx; the tube carrying air breathed in through the mouth is called the oropharynx. The nasopharynx and the oropharynx merge into the larynx. Because the oropharynx also carries swallowed substances, including food, water, and salivary secretions which must pass into the esophagus and then the stomach, the larynx is protected by a trap door called the epiglottis. The epiglottis prevents substances which have been swallowed, as well as substances which have been regurgitated (thrown up) from heading down into the larynx and toward the lungs.

A useful method of picturing the respiratory system is to imagine an upside-down tree. The larynx flows into the trachea, which is the tree trunk, and thus the broadest part of the respiratory tree. The trachea divides into two tree limbs, the right and left bronchi, each of which branches off into multiple smaller bronchi, which course through the tissue of the lung. Each bronchus divides into tubes of smaller and smaller diameter, finally ending in the terminal bronchioles. The air sacs of the lung, in which oxygen-carbon dioxide exchange actually takes place, are clustered at the ends of the bronchioles like the leaves of a tree, and are called alveoli.

The tissue of the lung which serves only a supportive role for the bronchi, bronchioles, and alveoli, is called the lung parenchyma.