Alveoli (air sacs) are important components of the lungs. They are responsible for the exchange of gases between the blood and the outside world. The alveoli ensure the intake of fresh air for breathing and the removal of carbon dioxide produced by breathing. If alveoli are damaged, breathing becomes massively restricted. Curative treatment options for damage to the alveoli do not currently exist; with appropriate therapies, some quality of life can be maintained.
What are alveoli?
Schematic diagram showing the anatomy and structure of the lungs and bronchi. Click to enlarge. The alveoli are central components of the lungs. They are located at the end of the bronchi or bronchioles. They are responsible for the smooth exchange of gases between the body and the environment. Humans have approximately 300 million alveoli. Alveoli are well protected by the bronchi in front of them, so they are usually not affected even by severe infections. However, if the alveoli are massively damaged or killed due to severe exposure to pollutants, respiratory function cannot be maintained. Once destroyed, alveoli do not grow back, nor can their function be taken over by other alveoli. Thus, diseases resulting from destruction of the alveoli cannot be treated curatively.
Anatomy and structure
The structure of the lung resembles a tree. The trachea (the trunk) opens into the lungs. There, the tube branches into innumerable branches, the bronchi. Very fine branches, the bronchioles, are attached to the bronchi. Attached to the bronchioles are small leaf-like extensions, the alveoli. Gas exchange takes place in the alveoli. There are a total of about 300 million alveoli in both lungs. Each alveolus has a diameter of about 0.2 millimeters. Spread out, this results in a total surface area of almost 100 square meters. By comparison, the skin has an area of about 2 square meters. The alveoli are surrounded by a network of hair-thin blood vessels. Between the blood vessels and the alveoli there is a permeable layer of skin, with the help of which gas exchange takes place. The skin layer is permeable in both directions, so that on the one hand fresh air can be released from the alveolus into the blood vessel. On the other hand, the alveolus takes in stale air and releases it to the outside. Alveoli are hollow on the inside. In the hollow spaces they can store the fresh air and the used air for a short period of time. Individual alveoli are separated from each other by a membrane.
Function and tasks
The central task of the alveoli is to ensure the exchange of gases between the body and the environment that takes place during respiration. During respiration, the lungs first take in fresh air from the environment. The air is transported through the trachea, bronchi and bronchial tubes to the alveoli. There, the alveoli store the respiratory air in a cavity and then release it through a thin layer of skin into the blood vessel that surrounds it. Gas exchange works in a similar way the other way around: the blood vessel transports the used exhaust air to the alveolus. There, the harmful carbon dioxide diffuses from the blood into the cavity of the alveoli. There it is briefly stored and then expelled into the environment during the next breath.
Diseases and ailments
Pulmonary alveoli do not usually cause any discomfort. Even during a severe cold, bronchitis or asthma, the alveoli are well protected by the bronchi and bronchial tubes. Only in the case of chronic damage to the bronchi can the alveoli also be damaged; normal breathing is then no longer possible. Breathing causes numerous harmful substances to enter the lungs. Under normal stress, the lungs can easily remove the pollutants with the help of the bronchi and alveoli. However, if the load is permanently too great, the mucous membranes of the bronchial tubes initially swell. In order to be able to remove the mucus, the person coughs and expels the mucus (sputum). If the stress continues, the mucus production and thus the narrowing of the airways progresses further and cannot be reversed, even if the exposure to pollutants ceases. As COPD (chronic obstructive pulmonary disease) progresses, the alveoli become damaged.The damage is manifested by complete destruction of the alveoli. So-called emphysema bubbles are formed. The emphysema bubbles inflate and take up considerable space in the lungs without serving any purpose. Lung capacity decreases, and the patient suffers increasing shortness of breath. In the worst case, the patient can no longer participate in daily life due to the shortness of breath and is relatively immobile. The most common cause of COPD is heavy smoking. Smokers are almost certain to develop COPD sooner or later.
