The ABCs of Breathing

If you have asthma, chronic obstructive pulmonary disease (COPD), or another lung disease, it helps to understand how the lungs work and to know what happens when these conditions affect them.

When you inhale, air travels down the back of your throat (pharynx), passes through your voice box (larynx) and goes into your windpipe (trachea). The trachea is divided into two air passages (main-stem bronchi); one leads to the left lung, and one to the right lung. The diaphragm, a dome-shaped muscle, lies below the lungs. It flattens to draw air in as you inhale and rises when you exhale.

The right lung has three sections, called lobes, and is slightly larger than the left lung, which has two lobes. The main-stem bronchi divide into smaller air passages called bronchioles. At the end of the bronchioles are tiny air sacs called alveoli, where oxygen and carbon dioxide are exchanged.

After absorbing oxygen, the blood flows from the lungs to the heart. It is then pumped through the body, providing oxygen to the cells of the tissues and organs. When the cells use the oxygen, carbon dioxide (CO2) is produced and transferred to the blood. The blood carries the CO2 back to the lungs, where it is removed when you exhale.

Your lungs are protected from harmful substances in a number of ways. The hair in the nose helps filter out large particles, and cilia (microscopic hairlike projections on cells that line the nose and larger airways of the lung) continually sweep back and forth to keep the air passages clear (cigarette smoke can damage cilia).

Mucus produced by the trachea and bronchial tubes helps trap dust, bacteria and other foreign substances before they can enter the lungs. Normally, the airways are open and free from inflammation and excess mucus.

In asthma, the lining of the airways becomes inflamed and swollen. The lining can make extra mucus, which clogs the airways. The muscles around the airways tighten, making the airways even narrower. Sometimes the airways can become so narrow that air has trouble getting in and out of the lungs, resulting in an asthma attack.

In chronic bronchitis, the lining of the bronchioles becomes inflamed and produces too much mucus. In some people, the swelling and excess mucus narrow the airways and restrict airflow in and out of the lungs, causing shortness of breath. The cilia also are damaged, preventing them from removing the excess mucus.

In emphysema, the walls of the alveoli lose their elasticity and become enlarged. As they get bigger, the diaphragm flattens, making it harder for the lungs to move air in and out. The bronchioles also become less elastic and become narrow or collapse upon exhalation. As a result, CO2 gets trapped in the airways and prevents oxygen from getting to the blood.

Updated by Remedy Health Media

Publication Review By: Peter B. Terry, M.D., M.A.

Published: 07 Aug 2013

Last Modified: 27 Jan 2015