Pneumonia - Description

The healthy human lung is normally free of disease-causing microorganisms, such as bacteria and viruses. The body has immune system (a complex defense system) is designed to keep it that way. For example, hairs in the nose trap large particles carried along by the air we breathe in. The epiglottis is a kind of trapdoor in the larynx (windpipe; pronounced LAYR-inx) that keeps food and other swallowed substances from entering the lungs. Mucus, a thick liquid, is produced throughout the respiratory (breathing) system to capture dust, bacteria, and other organisms. Cilia (pronounced SIL-ee-uh) are hairlike projections along the lining of the respiratory system that also trap and remove foreign objects from the body. Special types of white blood cells, called macrophages (pronounced MAK-ruh-faj), are also part of this defensive system. They are produced when foreign bodies enter the body to attack and destroy those bodies.

This system of defenses does not work perfectly, however. Sometimes organisms that can cause infection get into the lungs. For example, a person may be exposed to large amounts of smoke. There may be too many smoke particles for the body's defense system to remove. In such a case, the lungs may become infected and pneumonia can develop. the airways.

Conditions that Lead to Pneumonia

In many cases, the lungs become infected simply because they are overwhelmed with some foreign agent, such as bacteria or smoke particles. But a variety of conditions can increase the likelihood that a person will contract (catch) pneumonia. In these conditions, the person's lungs may already be weakened or damaged by some other problem. Some of these conditions include the following:

• Damage to the epiglottis. Stroke, seizures, alcohol, and various drugs can prevent the epiglottis from functioning normally. When this happens, materials that have been swallowed may get into the lungs, causing an infection there.
• Viruses. Viruses can damage the cilia that line the respiratory tract. Foreign bodies may then get into the lungs more easily, causing an infection. One such virus is HIV (the human immunodeficiency virus), which causes AIDS (see AIDS entry). Pneumonia is a major health problem for people with AIDS and those who have HIV in their bodies.
• Old age. As people grow older, their immune systems often become weaker. They are less able to fight off infections that once would not have been a problem.
• Chronic diseases. A chronic disease lasts for a very long time, usually many years. Examples of such diseases are asthma (see asthma entry), cystic fibrosis (see cystic fibrosis entry), and diseases of the nervous and muscular systems. These diseases often affect the epiglottis. A damaged epiglottis allows food and contaminated objects to get into the lungs, causing infections that can lead to pneumonia.
• Surgery. Pneumonia is a common complication of surgery. Some drugs used during surgery affect a person's normal breathing pattern. He or she may not be able to cough or breathe as deeply as usual. Foreign objects are not expelled from the respiratory tract. They may get into the lungs and cause an infection.