What is Asthma?

Introduction

The word asthma originates from an ancient Greek word meaning panting. Essentially, asthma is an inflammatory lung condition that makes it difficult to breathe properly.

When people inhale, the air travels through the following structures:

• Air passes into the lungs and flows through progressively smaller airways called bronchi and then bronchioles. The lungs contain millions of these airways.
• All bronchioles lead to alveoli, which are microscopic sacs where oxygen is taken in and carbon dioxide is expelled.

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Asthma is a chronic condition in which these airways undergo changes when stimulated by allergens or other environmental triggers. Such changes appear to be two specific responses:

• The hyperreactive response (also called hyperresponsiveness)
• The inflammatory response

These actions in the airway cause coughing, wheezing, and shortness of breath (dyspnea), the classic symptoms of asthma.

Hyperreactive Response

In the hyperreactive response, smooth muscles in the airways of the lungs constrict and narrow excessively in response to inhaled allergens or other irritants. Airways in everyone's lungs respond by constricting when exposed to allergens or irritants but there are major differences in the hyperreactive response that occurs in people with asthma:

• When people without asthma breathe in and out deeply, the airways relax and open to rid the lungs of the irritant.
• When people with asthma try to take those same deep breaths, their airways do not relax and narrow, causing patients to pant for breath. Smooth muscles in the airways of people with asthma may have a defect, perhaps a deficiency in a critical chemical that prevents the muscles from relaxing. And, during an asthma attack the airways narrow, making breathing difficult.

Inflammatory Response

The hyperreactive stage is followed by the inflammatory response, which generally contributes to asthma in the following way:

• In response to allergens or other environmental triggers, the immune system delivers white blood cells and other immune factors to the airways.
• These so-called inflammatory factors cause the airways to swell, to fill with fluid, and to produce a thick sticky mucus.
• This combination results in wheezing, breathlessness, an inability to exhale properly, and a phlegm-producing cough.

Click the icon to see an image of a normal bronchiole versus an asthmatic bronchiole.

Inflammation appears to be present in the lungs of all patients with asthma, even those with mild cases, and plays a key role in all forms of the disease.

Review Date: 05/03/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).